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Turning a 1/4 wave vertical upside down
I have a low power FM transmitter that I use for in my house and yard.
I want to put a 1/4 wave vertical on the roof of my home. The 1/4 wave vertical will be made as many have seen from a UHF panel mount connector with the vertical on the center pin and the four radials soldered to the holes for the screws. Like this, https://encrypted-tbn1.gstatic.com/i...M00RrltFyCH-LA Only bigger :-) Looking at the pattern of a 1/4 wave vertical, I think I could best cover my yard with the pattern upside down. Can I mount the antenna upside down? Is this feasible? If I did turn it upside down, what would the feedline do to the pattern? Is there a better physical layout to avoid pattern distortion caused by the feedline? Mikek |
Turning a 1/4 wave vertical upside down
On Sat, 30 Nov 2013 21:42:38 -0600, amdx wrote:
I have a low power FM transmitter that I use for in my house and yard. I want to put a 1/4 wave vertical on the roof of my home. The 1/4 wave vertical will be made as many have seen from a UHF panel mount connector with the vertical on the center pin and the four radials soldered to the holes for the screws. Like this, https://encrypted-tbn1.gstatic.com/i...M00RrltFyCH-LA Only bigger :-) Unless you use stiff elements, they will sag. At 100MHz, 1/4 wavelength is about 75 cm (2.5 ft) long. Looking at the pattern of a 1/4 wave vertical, I think I could best cover my yard with the pattern upside down. Think again please. Can I mount the antenna upside down? Yes. Is this feasible? Yes. It's commonly done with UHF antennas on mountain top sites. If I did turn it upside down, what would the feedline do to the pattern? The feed line will mangle the pattern. Is there a better physical layout to avoid pattern distortion caused by the feedline? Yes. Use a vertical dipole on a tower or a coaxial antenna on a vent pipe. The alleged problem with a ground plane antenna is that there is a slight vertical uptilt of the beam. It varies with the height above the rooftop ground, but my guess(tm) is maybe 5 to 10 degrees uptilt. I just ran a simple ground plane simulation using 4NEC2 and found that the uptilt is small when the vertical beamwidth of the ground plane is about 90 degrees. In other words, inverting the antenna isn't going to do much good at delivering the signal towards the ground. You're better off with an antenna that puts the main lobes where your receiver is located or perhaps has some gain and/or downtilt. Without a description of your house and yard, I can't offer any suggestions. Numbers please? You might find it useful to look at what the LPFM people are doing for antennas: https://www.google.com/search?q=lpfm+antenna&tbm=isch Remember, the stranger it looks, the better it works. Ummm... what problem are you trying to solve? -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Turning a 1/4 wave vertical upside down
On 11/30/2013 10:30 PM, Jeff Liebermann wrote:
On Sat, 30 Nov 2013 21:42:38 -0600, amdx wrote: I have a low power FM transmitter that I use for in my house and yard. I want to put a 1/4 wave vertical on the roof of my home. The 1/4 wave vertical will be made as many have seen from a UHF panel mount connector with the vertical on the center pin and the four radials soldered to the holes for the screws. Like this, https://encrypted-tbn1.gstatic.com/i...M00RrltFyCH-LA Only bigger :-) Unless you use stiff elements, they will sag. At 100MHz, 1/4 wavelength is about 75 cm (2.5 ft) long. Looking at the pattern of a 1/4 wave vertical, I think I could best cover my yard with the pattern upside down. Think again please. I did, a couple times. I wondered, how does the ground (the dirt) under the radial ground affect the pattern? Then I thought: The classic pattern is not exact, otherwise I'd get no signal in my house with the antenna on the roof. Also (I thinked) just changing from the 8" rubber ducky to the the 1/4 wave on the roof will make a huge difference. Can I mount the antenna upside down? Yes. Will I knew I could! We have an upside down building not far from here. The better question, is there a good reason to mount the antenna upside down? Is this feasible? Yes. It's commonly done with UHF antennas on mountain top sites. Darn, not an original idea! If I did turn it upside down, what would the feedline do to the pattern? The feed line will mangle the pattern. So why did I ask, I knew that. Is there a better physical layout to avoid pattern distortion caused by the feedline? Yes. Use a vertical dipole on a tower or a coaxial antenna on a vent pipe. Hmm, vertical dipole, But, then I'd miss the excitement of paralleling 90* of two 75 ohm coax cables and the measurements to match 37 ohms to 50 ohms. I wanted to see that happen. I guess I could still do the experiment. The alleged problem with a ground plane antenna is that there is a slight vertical uptilt of the beam. It varies with the height above the rooftop ground, but my guess(tm) is maybe 5 to 10 degrees uptilt. I just ran a simple ground plane simulation using 4NEC2 and found that the uptilt is small when the vertical beamwidth of the ground plane is about 90 degrees. In other words, inverting the antenna isn't going to do much good at delivering the signal towards the ground. You're better off with an antenna that puts the main lobes where your receiver is located or perhaps has some gain and/or downtilt. Without a description of your house and yard, I can't offer any suggestions. Numbers please? Ok, as you might have guessed, a lot of this is, as a previous boss of mine, used to call "mental masturbation" I do intend to mount an antenna outside (again), now, I'm not sure what type. The problem I'm solving is, in some areas of my yard, the radio signal gets buzzy, sometimes turning the radio will fix it, often I have to move the radio 5ft to get a clear signal. My transmitter is a CZH-05B, the power is switchable between 0.1 watt and 0.5 watts. I run it at 0.1 watt in an effort to keep myself out of trouble. Hmm, as I'm writing I noted I have two 3.0db attenuators before the antenna, as more keep myself out of trouble units. (Btw, I just modified a 13 element filter to put between the transmitter and the antenna. Someday I hope to have the equipment to analyze it and see how well it works ( how well I did). I started with a TFD6102A and wound new coils and added capacitance as needed. I have not installed it yet.) I recently bought an HP 141T/8553, if I find a 8555 at a reasonable price, I'll buy it. The receive area is small, 120" x 115", the antenna will be mounted 13" in from the long dimension and 16" in from the smaller dimension, basically in the corner of the lot, mounted 16 ft high. Jeff, at this point, I have convinced myself putting a gain antenna on the roof will solve any problem I may have. If not I can still remove 6db of attenuation. So unless you want some mental exercise, don't over do it! I think you suggested a vertical dipole with downtilt. Any thoughts about matching, I have no clue how tolerant this little transmitter is. Hmm, maybe put a 3db attenuator on the transmitter output, into the LPF, then another 3db attenuator between the LPF and the antenna. Then my transmitter's happy, and my filter is happy. You might find it useful to look at what the LPFM people are doing for antennas: https://www.google.com/search?q=lpfm+antenna&tbm=isch Remember, the stranger it looks, the better it works. Ummm... what problem are you trying to solve? Who said I have a problem? ;-) I'll add, I have messed with the Ramsey FM transmitter and a couple of others, This transmitter works great, and they're down to about $60 now, half what I paid two years ago. The newer models go up to 7 watts, if you can believe the specs. I run my internet radio into the FM transmitter so I can listen to it around the home. Mikek |
Turning a 1/4 wave vertical upside down
On 12/1/2013 10:49 AM, amdx wrote:
On 11/30/2013 10:30 PM, Jeff Liebermann wrote: On Sat, 30 Nov 2013 21:42:38 -0600, amdx wrote: I have a low power FM transmitter that I use for in my house and yard. I want to put a 1/4 wave vertical on the roof of my home. The 1/4 wave vertical will be made as many have seen from a UHF panel mount connector with the vertical on the center pin and the four radials soldered to the holes for the screws. Like this, https://encrypted-tbn1.gstatic.com/i...M00RrltFyCH-LA Only bigger :-) Unless you use stiff elements, they will sag. At 100MHz, 1/4 wavelength is about 75 cm (2.5 ft) long. Looking at the pattern of a 1/4 wave vertical, I think I could best cover my yard with the pattern upside down. Think again please. I did, a couple times. I wondered, how does the ground (the dirt) under the radial ground affect the pattern? Then I thought: The classic pattern is not exact, otherwise I'd get no signal in my house with the antenna on the roof. Also (I thinked) just changing from the 8" rubber ducky to the the 1/4 wave on the roof will make a huge difference. Can I mount the antenna upside down? Yes. Will I knew I could! We have an upside down building not far from here. The better question, is there a good reason to mount the antenna upside down? Is this feasible? Yes. It's commonly done with UHF antennas on mountain top sites. Darn, not an original idea! If I did turn it upside down, what would the feedline do to the pattern? The feed line will mangle the pattern. So why did I ask, I knew that. Is there a better physical layout to avoid pattern distortion caused by the feedline? Yes. Use a vertical dipole on a tower or a coaxial antenna on a vent pipe. Hmm, vertical dipole, But, then I'd miss the excitement of paralleling 90* of two 75 ohm coax cables and the measurements to match 37 ohms to 50 ohms. I wanted to see that happen. I guess I could still do the experiment. The alleged problem with a ground plane antenna is that there is a slight vertical uptilt of the beam. It varies with the height above the rooftop ground, but my guess(tm) is maybe 5 to 10 degrees uptilt. I just ran a simple ground plane simulation using 4NEC2 and found that the uptilt is small when the vertical beamwidth of the ground plane is about 90 degrees. In other words, inverting the antenna isn't going to do much good at delivering the signal towards the ground. You're better off with an antenna that puts the main lobes where your receiver is located or perhaps has some gain and/or downtilt. Without a description of your house and yard, I can't offer any suggestions. Numbers please? Ok, as you might have guessed, a lot of this is, as a previous boss of mine, used to call "mental masturbation" I do intend to mount an antenna outside (again), now, I'm not sure what type. The problem I'm solving is, in some areas of my yard, the radio signal gets buzzy, sometimes turning the radio will fix it, often I have to move the radio 5ft to get a clear signal. My transmitter is a CZH-05B, the power is switchable between 0.1 watt and 0.5 watts. I run it at 0.1 watt in an effort to keep myself out of trouble. Hmm, as I'm writing I noted I have two 3.0db attenuators before the antenna, as more keep myself out of trouble units. (Btw, I just modified a 13 element filter to put between the transmitter and the antenna. Someday I hope to have the equipment to analyze it and see how well it works ( how well I did). I started with a TFD6102A and wound new coils and added capacitance as needed. I have not installed it yet.) I recently bought an HP 141T/8553, if I find a 8555 at a reasonable price, I'll buy it. The receive area is small, 120" x 115", the antenna will be mounted 13" in from the long dimension and 16" in from the smaller dimension, basically in the corner of the lot, mounted 16 ft high. Jeff, at this point, I have convinced myself putting a gain antenna on the roof will solve any problem I may have. If not I can still remove 6db of attenuation. So unless you want some mental exercise, don't over do it! I think you suggested a vertical dipole with downtilt. Any thoughts about matching, I have no clue how tolerant this little transmitter is. Hmm, maybe put a 3db attenuator on the transmitter output, into the LPF, then another 3db attenuator between the LPF and the antenna. Then my transmitter's happy, and my filter is happy. You might find it useful to look at what the LPFM people are doing for antennas: https://www.google.com/search?q=lpfm+antenna&tbm=isch Remember, the stranger it looks, the better it works. Ummm... what problem are you trying to solve? Who said I have a problem? ;-) I'll add, I have messed with the Ramsey FM transmitter and a couple of others, This transmitter works great, and they're down to about $60 now, half what I paid two years ago. The newer models go up to 7 watts, if you can believe the specs. I run my internet radio into the FM transmitter so I can listen to it around the home. Mikek If you're in the United States, you are subject to FCC Part 15 rules. These rules are based (amongst other things) on Effective Radiated Power (ERP). So if you install an antenna with gain, you have to cut your power. And IIRC, the transmitter must also be certified as a Part 15 device, which it doesn't look like yours is - at least there is no indication of that. If you get caught (and it seems the FCC has been clamping down on unlicensed stations), you will be in for a hefty fine. Unless you have a very large yard, you should be able to cover it with a certified transmitter -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
Turning a 1/4 wave vertical upside down
On Sun, 01 Dec 2013 09:49:32 -0600, amdx wrote:
Think again please. I did, a couple times. Keep trying. Enlightenment requires suffering. Ask any philosopher. I wondered, how does the ground (the dirt) under the radial ground affect the pattern? Actually, almost anything conductive or absorptive affects the antenna pattern. In the case of "ground", I'm not talking about earth ground. Rather, all the metal and conductive components the comprise your house. Then I thought: The classic pattern is not exact, otherwise I'd get no signal in my house with the antenna on the roof. Correct. Theory is idealized reality. To see reality, drugs like LSD are sometimes helpful. When searching for enlightenment in antenna design, I prefer prescription pain killers, to dull the suffering. Also (I thinked) just changing from the 8" rubber ducky to the the 1/4 wave on the roof will make a huge difference. That depends on what's inside the 8" rubber ducky antenna. 1 wavelength at 100 Mhz is about 118" making 8" = 0.07 wavelengths long. That's right at the borderline where the antenna pattern falls apart and gain starts to drop. Of course, that assumes that the rubber ducky is properly matched to 75 ohms or is a helical antenna. What happens with short monopole antennas (not rubber ducky antennas) is that as the antenna shrinks, the gain remains roughly the same as a 1/4 wave monopole. With matching, the bandwidth becomes narrow. (You can have gain, bandwidth or size... pick any two). I think rubber ducky (end fed helical) antennas are roughly the same. However, at 0.1 wavelengths, the gain finally starts to drop. I did a crude study of the effect on monopoles: http://www.LearnByDestroying.com/jeffl/antennas/Monopole/index.html The numbers in the file names are the antenna length. For example, monopole_0_0250 is 1/4 wave long. The NEC files are suppose to be in the NEC directory, but seems to have evaporated. I'll fix later. Will I knew I could! We have an upside down building not far from here. The better question, is there a good reason to mount the antenna upside down? Yes, if you are on top of a mountain, and are stuck with antenna that is end fed and suffers from pattern uptilt. Using a realistic model of both the structure and the antenna, it can be demonstrated that most of the RF is going to heating the sky and talking to birds. In other words, little RF is going to the ground, where the mobiles and handhelds are hiding. By inverting the antenna, usually on a tower outrigger, the RF is redirected BELOW the horizon and more towards the ground. Such problems are very common at higher frequencies (above 400 MHz) where vertical radiation patterns are narrow, and gains are high. http://www.proxim.com/products/knowledge-center/calculations/calculations-downtilt-coverage-radius However, you're probably not on top of a mountain and do not have enough gain for vertical radiation angle to be a problem at 100 MHz. Darn, not an original idea! I've never had an original idea in my life. Everything I say or do is based on the work of others (shoulders of giants and such). The trick to an original idea is getting away with stealing the idea, and making it sound original. See the broken US patent system for how that works. If I did turn it upside down, what would the feedline do to the pattern? The feed line will mangle the pattern. So why did I ask, I knew that. Second opinion perhaps? The question really boils down to how does a tower or pipe affect the antenna pattern since it's the mounting structure that has a bigger effect than the coax. Of course, that assume that the antenna has a balun to prevent the coax from radiating, which can produce all kinds of disgusting changes to the pattern. Hmm, vertical dipole, But, then I'd miss the excitement of paralleling 90* of two 75 ohm coax cables and the measurements to match 37 ohms to 50 ohms. I wanted to see that happen. I guess I could still do the experiment. Not much happens. The mismatch loss between 37 and 50 ohms is about 0.1dB. You can be rather sloppy with coax cables and antenna impedances and still have a system that sorta works. I use 50 and 75 ohm coax cables almost interchangeably with problems. The problems appear if the transmitter is unable to transmit into a mismatch and protests by either shutting down, lowering the TX power, or going into oscillation. all these are possible and should be tested before using a mismatched antenna. A mismatch will also have some effect to the antenna pattern. Where a perfect match is required are for situations where the reflected power is capable of doing some damage (high TX power), where you need every bit of RX sensitivity you can squeeze out of the system (satellite work), or you simply want the very best system. I don't think your FM BCB setup qualifies for any of these. Ok, as you might have guessed, a lot of this is, as a previous boss of mine, used to call "mental masturbation" http://en.wikipedia.org/wiki/Thought_experiment The trouble with antennas is that you can't see the RF. We use test equipment as a blind man uses a cane. At best, you can only get a rough impression of what is happening. There are always surprises. Besides, it's amazing how much better things work if you think or model before you build. I do intend to mount an antenna outside (again), now, I'm not sure what type. The problem I'm solving is, in some areas of my yard, the radio signal gets buzzy, sometimes turning the radio will fix it, often I have to move the radio 5ft to get a clear signal. My transmitter is a CZH-05B, the power is switchable between 0.1 watt and 0.5 watts. I run it at 0.1 watt in an effort to keep myself out of trouble. Hmm, as I'm writing I noted I have two 3.0db attenuators before the antenna, as more keep myself out of trouble units. I think if you simply calculate the path loss of this system, you're going to be hurting for sufficient signal. I'm too lazy to do it right now. Based on previous pirate radio experiences, you'll be lucky if you get 100 ft range to a portable radio. Try a range test with the antenna near the ground, and just walking away until the signal gets noisy. (Btw, I just modified a 13 element filter to put between the transmitter and the antenna. Someday I hope to have the equipment to analyze it and see how well it works ( how well I did). I started with a TFD6102A and wound new coils and added capacitance as needed. I have not installed it yet.) I recently bought an HP 141T/8553, if I find a 8555 at a reasonable price, I'll buy it. Heh-heh. Make me rich and a broken 8555 can be yours. I have 3 of them but only 1 works, so this will be a repair job. I can probably fix it, but don't have the time or incentive. http://www.LearnByDestroying.com/jeffl/pics/home/slides/test-equip-mess.html You'll find that the hp8554B plugin (0-1200MHz) is more useful for FM BCB use. A 13 element filter is going to be lossy. How lossy depends on the design and construction. I suggest you make some measurements or just remove the filter and see what happens. The receive area is small, 120" x 115", the antenna will be mounted 13" in from the long dimension and 16" in from the smaller dimension, basically in the corner of the lot, mounted 16 ft high. With a 90 degree vertical radiation pattern, height doesn't really matter. Just get it closer to the receiver and you should be ok. Jeff, at this point, I have convinced myself putting a gain antenna on the roof will solve any problem I may have. Are you sure? Putting it on the roof will move the receiver about 15ft further away from the antenna and add some minor coax cable losses. That might be useful if you want to illuminate the neighborhood, but if you're already having signal strength problems, it's just going to make it worse. Also, do you have any idea of how large a "gain antenna" will be at 100 MHz? You might be better of with a dummy load and leaky coax snaked through the yard. If not I can still remove 6db of attenuation. So unless you want some mental exercise, don't over do it! Mental or metal exercise? I get to help move a 2 ton mill into a friends garage today. The exercise will not be mental. I'm suppose to be the "safety" officer, which is a little like hiring the fox to guard the hen house. If you don't hear from me, you can guess what happened. For your amusement. I'll turn it into a web page eventually: http://www.learnbydestroying.com/jeffl/antennas/dish-move-project/ Moving and aligning big 600 lb dish antennas is easy. Polar mount alignments are easy. Equatorial mounts are difficult. I had a little too much fun with the cutting torch. I think you suggested a vertical dipole with downtilt. Any thoughts about matching, I have no clue how tolerant this little transmitter is. Build a folded dipole out of twinlead and strips of dry pine or plastic. Plenty of instructions on the web. Add a 300 ohm to 75 ohm balun to match the RG-6/u. Mount it horizontally or vertically, it doesn't matter. Position it as close to your working area as possible. Do whatever is necessary to keep it away from conductive or absorptive objects, such as walls, trees, towers, poles, people, and junk. Optimizing a wide beamwidth pattern is a waste of effort. Don't read these: http://www.pcs-electronics.com/guide_antenna.php http://www.radiobrandy.com/FMAntenna.html http://www.part15.us http://www.radiobrandy.com They might give you some more ideas and produce more mental masturbation. Hmm, maybe put a 3db attenuator on the transmitter output, into the LPF, then another 3db attenuator between the LPF and the antenna. Then my transmitter's happy, and my filter is happy. Have you measured your power output? A 100 MHz scope across a 50 ohm load will suffice. (Remember that it's -3dB down at 100MHz). Measure the peak to peak voltage. Divided by 2.8 to get RMS voltage. Square that and divide by your dummy load resistance to get power. Ummm... what problem are you trying to solve? Who said I have a problem? ;-) If people did not have problems to solve, nothing would ever happen. If you need a problem, just ask, and I'll supply one for you. I'll add, I have messed with the Ramsey FM transmitter and a couple of others, This transmitter works great, and they're down to about $60 now, half what I paid two years ago. The newer models go up to 7 watts, if you can believe the specs. Define "works great". You wouldn't be asking such questions if it works as expected. I run my internet radio into the FM transmitter so I can listen to it around the home. I just turn up the volume control to get the same effect. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Turning a 1/4 wave vertical upside down
Before too much theorizing takes place, why not try just placing it in a
convenient location in the house -- you might be pleasantly surprised. If that doesn't work, then, and only then, it becomes a technical problem. Irv VE6BP "amdx" wrote in message ... I have a low power FM transmitter that I use for in my house and yard. I want to put a 1/4 wave vertical on the roof of my home. The 1/4 wave vertical will be made as many have seen from a UHF panel mount connector with the vertical on the center pin and the four radials soldered to the holes for the screws. Like this, https://encrypted-tbn1.gstatic.com/i...M00RrltFyCH-LA Only bigger :-) Looking at the pattern of a 1/4 wave vertical, I think I could best cover my yard with the pattern upside down. Can I mount the antenna upside down? Is this feasible? If I did turn it upside down, what would the feedline do to the pattern? Is there a better physical layout to avoid pattern distortion caused by the feedline? Mikek |
Turning a 1/4 wave vertical upside down
On 12/1/2013 11:29 AM, Jeff Liebermann wrote:
On Sun, 01 Dec 2013 09:49:32 -0600, amdx wrote: Think again please. I did, a couple times. Keep trying. Enlightenment requires suffering. Ask any philosopher. I'm only a little masochistic, I'll suffer some but unless it's something I really want I'm easily distracted. I wondered, how does the ground (the dirt) under the radial ground affect the pattern? Actually, almost anything conductive or absorptive affects the antenna pattern. In the case of "ground", I'm not talking about earth ground. Rather, all the metal and conductive components the comprise your house. Then I thought: The classic pattern is not exact, otherwise I'd get no signal in my house with the antenna on the roof. Correct. Theory is idealized reality. To see reality, drugs like LSD are sometimes helpful. When searching for enlightenment in antenna design, I prefer prescription pain killers, to dull the suffering. Ya, I have those for problems between S1/L5 and L5/L4, some days I can get a lot done other days, I'd rather watch TV. Also (I thinked) just changing from the 8" rubber ducky to the the 1/4 wave on the roof will make a huge difference. That depends on what's inside the 8" rubber ducky antenna. 1 wavelength at 100 Mhz is about 118" making 8" = 0.07 wavelengths long. That's right at the borderline where the antenna pattern falls apart and gain starts to drop. Of course, that assumes that the rubber ducky is properly matched to 75 ohms or is a helical antenna. What happens with short monopole antennas (not rubber ducky antennas) is that as the antenna shrinks, the gain remains roughly the same as a 1/4 wave monopole. With matching, the bandwidth becomes narrow. (You can have gain, bandwidth or size... pick any two). I think rubber ducky (end fed helical) antennas are roughly the same. However, at 0.1 wavelengths, the gain finally starts to drop. I did a crude study of the effect on monopoles: http://www.LearnByDestroying.com/jeffl/antennas/Monopole/index.html The numbers in the file names are the antenna length. For example, monopole_0_0250 is 1/4 wave long. The NEC files are suppose to be in the NEC directory, but seems to have evaporated. I'll fix later. Will I knew I could! We have an upside down building not far from here. The better question, is there a good reason to mount the antenna upside down? Yes, if you are on top of a mountain, and are stuck with antenna that is end fed and suffers from pattern uptilt. Using a realistic model of both the structure and the antenna, it can be demonstrated that most of the RF is going to heating the sky and talking to birds. In other words, little RF is going to the ground, where the mobiles and handhelds are hiding. By inverting the antenna, usually on a tower outrigger, the RF is redirected BELOW the horizon and more towards the ground. Such problems are very common at higher frequencies (above 400 MHz) where vertical radiation patterns are narrow, and gains are high. http://www.proxim.com/products/knowledge-center/calculations/calculations-downtilt-coverage-radius However, you're probably not on top of a mountain and do not have enough gain for vertical radiation angle to be a problem at 100 MHz. Darn, not an original idea! I've never had an original idea in my life. Everything I say or do is based on the work of others (shoulders of giants and such). The trick to an original idea is getting away with stealing the idea, and making it sound original. See the broken US patent system for how that works. I might have back in the 70s I thought about using a modulated laser to do the wood burning pictures. Might have been there early enough. Just talked with a laser engraver yesterday, prompted my mind. btw, could you make PCBs with a laser? If I did turn it upside down, what would the feedline do to the pattern? The feed line will mangle the pattern. So why did I ask, I knew that. Second opinion perhaps? The question really boils down to how does a tower or pipe affect the antenna pattern since it's the mounting structure that has a bigger effect than the coax. Of course, that assume that the antenna has a balun to prevent the coax from radiating, which can produce all kinds of disgusting changes to the pattern. Hmm, vertical dipole, But, then I'd miss the excitement of paralleling 90* of two 75 ohm coax cables and the measurements to match 37 ohms to 50 ohms. I wanted to see that happen. I guess I could still do the experiment. Not much happens. The mismatch loss between 37 and 50 ohms is about 0.1dB. You can be rather sloppy with coax cables and antenna impedances and still have a system that sorta works. I use 50 and 75 ohm coax cables almost interchangeably with problems. The problems appear if the transmitter is unable to transmit into a mismatch and protests by either shutting down, lowering the TX power, or going into oscillation. all these are possible and should be tested before using a mismatched antenna. A mismatch will also have some effect to the antenna pattern. Where a perfect match is required are for situations where the reflected power is capable of doing some damage (high TX power), where you need every bit of RX sensitivity you can squeeze out of the system (satellite work), or you simply want the very best system. I don't think your FM BCB setup qualifies for any of these. Ok, as you might have guessed, a lot of this is, as a previous boss of mine, used to call "mental masturbation" http://en.wikipedia.org/wiki/Thought_experiment The trouble with antennas is that you can't see the RF. We use test equipment as a blind man uses a cane. At best, you can only get a rough impression of what is happening. There are always surprises. Besides, it's amazing how much better things work if you think or model before you build. I do intend to mount an antenna outside (again), now, I'm not sure what type. The problem I'm solving is, in some areas of my yard, the radio signal gets buzzy, sometimes turning the radio will fix it, often I have to move the radio 5ft to get a clear signal. My transmitter is a CZH-05B, the power is switchable between 0.1 watt and 0.5 watts. I run it at 0.1 watt in an effort to keep myself out of trouble. Hmm, as I'm writing I noted I have two 3.0db attenuators before the antenna, as more keep myself out of trouble units. I think if you simply calculate the path loss of this system, you're going to be hurting for sufficient signal. I'm too lazy to do it right now. Based on previous pirate radio experiences, you'll be lucky if you get 100 ft range to a portable radio. Try a range test with the antenna near the ground, and just walking away until the signal gets noisy. Ok, one data set! I have the transmitter then a 3db att. then my LPF then another 3 db att. and the rubber ducky. I walked 250ft before noise showed up, then I went back and ran the antenna straight out of the transmitter. As you might think things did not work out as expected. I did not get as far with just the antenna. About 10 or 15ft less. So, I cruised the yard looking for poor reception, I found two spots, but move slightly and it's better. (Btw, I just modified a 13 element filter to put between the transmitter and the antenna. Someday I hope to have the equipment to analyze it and see how well it works ( how well I did). I started with a TFD6102A and wound new coils and added capacitance as needed. I have not installed it yet.) I recently bought an HP 141T/8553, if I find a 8555 at a reasonable price, I'll buy it. Heh-heh. Make me rich and a broken 8555 can be yours. I have 3 of them but only 1 works, so this will be a repair job. I can probably fix it, but don't have the time or incentive. http://www.LearnByDestroying.com/jeffl/pics/home/slides/test-equip-mess.html You'll find that the hp8554B plugin (0-1200MHz) is more useful for FM BCB use. I'd need to have a working unit, I'd have major problems with a repair. Can't I do with the 8555 anything I can do with the 8554? A 13 element filter is going to be lossy. How lossy depends on the design and construction. I suggest you make some measurements or just remove the filter and see what happens. It didn't show it's self as causing signal degradation. (1 data set) That's why I want the 8555! The receive area is small, 120" x 115", the antenna will be mounted 13" in from the long dimension and 16" in from the smaller dimension, basically in the corner of the lot, mounted 16 ft high. With a 90 degree vertical radiation pattern, height doesn't really matter. Just get it closer to the receiver and you should be ok. Jeff, at this point, I have convinced myself putting a gain antenna on the roof will solve any problem I may have. Are you sure? No. Putting it on the roof will move the receiver about 15ft further away from the antenna and add some minor coax cable losses. That might be useful if you want to illuminate the neighborhood, but if you're already having signal strength problems, it's just going to make it worse. Also, do you have any idea of how large a "gain antenna" will be at 100 MHz? You might be better of with a dummy load and leaky coax snaked through the yard. If not I can still remove 6db of attenuation. So unless you want some mental exercise, don't over do it! Mental or metal exercise? I get to help move a 2 ton mill into a friends garage today. The exercise will not be mental. I'm suppose to be the "safety" officer, which is a little like hiring the fox to guard the hen house. If you don't hear from me, you can guess what happened. For your amusement. I'll turn it into a web page eventually: http://www.learnbydestroying.com/jeffl/antennas/dish-move-project/ Moving and aligning big 600 lb dish antennas is easy. Polar mount alignments are easy. Equatorial mounts are difficult. I had a little too much fun with the cutting torch. I think you suggested a vertical dipole with downtilt. Any thoughts about matching, I have no clue how tolerant this little transmitter is. Build a folded dipole out of twinlead and strips of dry pine or plastic. Plenty of instructions on the web. Add a 300 ohm to 75 ohm balun to match the RG-6/u. Mount it horizontally or vertically, it doesn't matter. Position it as close to your working area as possible. Do whatever is necessary to keep it away from conductive or absorptive objects, such as walls, trees, towers, poles, people, and junk. Optimizing a wide beamwidth pattern is a waste of effort. Don't read these: http://www.pcs-electronics.com/guide_antenna.php http://www.radiobrandy.com/FMAntenna.html http://www.part15.us http://www.radiobrandy.com They might give you some more ideas and produce more mental masturbation. Hmm, maybe put a 3db attenuator on the transmitter output, into the LPF, then another 3db attenuator between the LPF and the antenna. Then my transmitter's happy, and my filter is happy. Have you measured your power output? A 100 MHz scope across a 50 ohm load will suffice. (Remember that it's -3dB down at 100MHz). Measure the peak to peak voltage. Divided by 2.8 to get RMS voltage. Square that and divide by your dummy load resistance to get power. I feel like you getting even for the MFJ1800 :-) I have a 300Mhz scope, just to complicate things. Measured 7.5Vpp. Sooo, I get 0.143 watts, so much for spec's. If I install the rubber ducky in place of the 50 ohm, I get 8.3Vpp. Later, I'll connect my MFJ259 to the rubber ducky, and see what it says. Ummm... what problem are you trying to solve? Who said I have a problem? ;-) If people did not have problems to solve, nothing would ever happen. If you need a problem, just ask, and I'll supply one for you. I'll add, I have messed with the Ramsey FM transmitter and a couple of others, This transmitter works great, and they're down to about $60 now, half what I paid two years ago. The newer models go up to 7 watts, if you can believe the specs. Define "works great". You wouldn't be asking such questions if it works as expected. Ya, maybe, but I'm running low power through 6db of attenuation with two walls and an aluminum screened porch between my problem area and the transmitter. Problem area is near my work shed and other side of the metal bar greenhouse. Minor problems, like I say I can move the radio 5ft and solve the problem. I run my internet radio into the FM transmitter so I can listen to it around the home. I just turn up the volume control to get the same effect. The neighbors would think I'm weird, I listen to Science 360, Gunsmoke, Phil Hendrie, what a train wreck! Need to go take over for my wife at the business, I'll reread what you said here and look at links when I get to work, it's a tough job (well, not really) but somebodies got to do it. Thanks, Mikek |
Turning a 1/4 wave vertical upside down
On 12/1/2013 11:48 AM, Irv Finkleman wrote:
Before too much theorizing takes place, why not try just placing it in a convenient location in the house -- you might be pleasantly surprised. If that doesn't work, then, and only then, it becomes a technical problem. Irv VE6BP That's good advice, except I have three different audio inputs that all land where I now have the transmitter. Besides, we like technical problems! :-) After my last response to Jeff when I measured the output voltage, I just realized I can check the loss through the LPF. Hot dog! Can't wait to get home. Mikek |
Turning a 1/4 wave vertical upside down
El 01-12-13 16:49, amdx escribió:
On 11/30/2013 10:30 PM, Jeff Liebermann wrote: On Sat, 30 Nov 2013 21:42:38 -0600, amdx wrote: I have a low power FM transmitter that I use for in my house and yard. I want to put a 1/4 wave vertical on the roof of my home. The 1/4 wave vertical will be made as many have seen from a UHF panel mount connector with the vertical on the center pin and the four radials soldered to the holes for the screws. Like this, https://encrypted-tbn1.gstatic.com/i...M00RrltFyCH-LA Only bigger :-) Unless you use stiff elements, they will sag. At 100MHz, 1/4 wavelength is about 75 cm (2.5 ft) long. Looking at the pattern of a 1/4 wave vertical, I think I could best cover my yard with the pattern upside down. Think again please. I did, a couple times. I wondered, how does the ground (the dirt) under the radial ground affect the pattern? Then I thought: The classic pattern is not exact, otherwise I'd get no signal in my house with the antenna on the roof. Also (I thinked) just changing from the 8" rubber ducky to the the 1/4 wave on the roof will make a huge difference. Can I mount the antenna upside down? Yes. Will I knew I could! We have an upside down building not far from here. The better question, is there a good reason to mount the antenna upside down? Is this feasible? Yes. It's commonly done with UHF antennas on mountain top sites. Darn, not an original idea! If I did turn it upside down, what would the feedline do to the pattern? The feed line will mangle the pattern. So why did I ask, I knew that. Is there a better physical layout to avoid pattern distortion caused by the feedline? Yes. Use a vertical dipole on a tower or a coaxial antenna on a vent pipe. Hmm, vertical dipole, But, then I'd miss the excitement of paralleling 90* of two 75 ohm coax cables and the measurements to match 37 ohms to 50 ohms. I wanted to see that happen. I guess I could still do the experiment. The alleged problem with a ground plane antenna is that there is a slight vertical uptilt of the beam. It varies with the height above the rooftop ground, but my guess(tm) is maybe 5 to 10 degrees uptilt. I just ran a simple ground plane simulation using 4NEC2 and found that the uptilt is small when the vertical beamwidth of the ground plane is about 90 degrees. In other words, inverting the antenna isn't going to do much good at delivering the signal towards the ground. You're better off with an antenna that puts the main lobes where your receiver is located or perhaps has some gain and/or downtilt. Without a description of your house and yard, I can't offer any suggestions. Numbers please? Ok, as you might have guessed, a lot of this is, as a previous boss of mine, used to call "mental masturbation" I do intend to mount an antenna outside (again), now, I'm not sure what type. The problem I'm solving is, in some areas of my yard, the radio signal gets buzzy, sometimes turning the radio will fix it, often I have to move the radio 5ft to get a clear signal. My transmitter is a CZH-05B, the power is switchable between 0.1 watt and 0.5 watts. I run it at 0.1 watt in an effort to keep myself out of trouble. Hmm, as I'm writing I noted I have two 3.0db attenuators before the antenna, as more keep myself out of trouble units. (Btw, I just modified a 13 element filter to put between the transmitter and the antenna. Someday I hope to have the equipment to analyze it and see how well it works ( how well I did). I started with a TFD6102A and wound new coils and added capacitance as needed. I have not installed it yet.) I recently bought an HP 141T/8553, if I find a 8555 at a reasonable price, I'll buy it. The receive area is small, 120" x 115", the antenna will be mounted 13" in from the long dimension and 16" in from the smaller dimension, basically in the corner of the lot, mounted 16 ft high. You mentioned 0.1 W with 2, 3 dB attenuators, so you may have around 10..20mW at the antenna (depending on cable loss). This should be more then enough to cover your yard if you find some clear frequency. I would just try the quarter wave antenna with three or 4 radials on the roof (not up side down). Due to scattering on the roof, and may be some common mode current on the feed line, you will have sufficient signal indoors. If you live in shielded room or heavy bunker/shelter, you may not have indoor coverage. You may give us some height and lot size info. Jeff, at this point, I have convinced myself putting a gain antenna on the roof will solve any problem I may have. If not I can still remove 6db of attenuation. So unless you want some mental exercise, don't over do it! I think you suggested a vertical dipole with downtilt. Any thoughts about matching, I have no clue how tolerant this little transmitter is. Hmm, maybe put a 3db attenuator on the transmitter output, into the LPF, then another 3db attenuator between the LPF and the antenna. Then my transmitter's happy, and my filter is happy. You might find it useful to look at what the LPFM people are doing for antennas: https://www.google.com/search?q=lpfm+antenna&tbm=isch Remember, the stranger it looks, the better it works. Ummm... what problem are you trying to solve? Who said I have a problem? ;-) I'll add, I have messed with the Ramsey FM transmitter and a couple of others, This transmitter works great, and they're down to about $60 now, half what I paid two years ago. The newer models go up to 7 watts, if you can believe the specs. I run my internet radio into the FM transmitter so I can listen to it around the home. Mikek Best regards, -- Wim PA3DJS www.tetech.nl Please remove abc first in case of PM |
Turning a 1/4 wave vertical upside down
On Sun, 01 Dec 2013 13:05:23 -0600, amdx wrote:
I'm only a little masochistic, I'll suffer some but unless it's something I really want I'm easily distracted. For me, it's the math that causes the most suffering. I have 3 calculators, one PC, and a Mac on my desk, and I still can't get the right answer. Maybe I should buy an iPad? It is impossible to achieve enlightenment without suffering. In other words, things become more obvious after you screw everything up, destroy some equipment, and injure yourself. It becomes very plain how something works after it tries to kill you. You can do it slowly, rapidly, or periodically, they all work. In some cultures, flagellation has been shown to be effective. The only problem is that this all applies to the models of antennas, not the actual performance. That's pure magic. I might have back in the 70s I thought about using a modulated laser to do the wood burning pictures. Might have been there early enough. Just talked with a laser engraver yesterday, prompted my mind. btw, could you make PCBs with a laser? Sure. No copper required. Just burn some tracks into the FR4/G10 with the laser. They should be sufficiently conductive to work with low power circuits using solder paste of connections. However, to be sure, you might want to measure the ohms/square of carbonized PCB material. However, you're behind the times. The hot ticket are printed PCB's using an inkjet printer and nanoparticle inks. I wrote a rant on the topic in a mailing list last week. Unfortunately, the archive is for members only. Light reading: http://dl.acm.org/citation.cfm?id=2493486 http://www.techweekeurope.co.uk/news/silver-ink-solution-for-cheaper-faster-flexible-circuits-54967 Years ago, I thought I had a better idea of PCB construction. I would roll a rounded point over the unplated G10/FR14 PCB forming groves for traces. I would then fill the grooves with conductive solder paste using ordinary silk screen techniques. When I tried it, it actually worked. However, the process was slow because anything faster than maybe 1/2" per second would burn the PCB from the friction. Ok, one data set! I have the transmitter then a 3db att. then my LPF then another 3 db att. and the rubber ducky. I walked 250ft before noise showed up, then I went back and ran the antenna straight out of the transmitter. As you might think things did not work out as expected. I did not get as far with just the antenna. About 10 or 15ft less. Ummm... a good question would be why that's happening. Plenty of possibilities including that your yard is an RF black hole. However, my guess(tm) is that nothing is very well matched to 50/75 ohms and the coax, attenuator, and LPF are radiating (leaking). You should probably fix that although 250 ft is more than I would have expected with a commodity receiver. Heh-heh. Make me rich and a broken 8555 can be yours. I have 3 of them but only 1 works, so this will be a repair job. I can probably fix it, but don't have the time or incentive. http://www.LearnByDestroying.com/jeffl/pics/home/slides/test-equip-mess.html You'll find that the hp8554B plugin (0-1200MHz) is more useful for FM BCB use. I'd need to have a working unit, I'd have major problems with a repair. Can't I do with the 8555 anything I can do with the 8554? I charge extra if it works. The 8554 goes to 1.2Ghz. The hp8555a goes to from 10 MHz to 18GHz. With an external mixer to 43GHz. They're quite different plug-ins. You'll need an external hp8445b preselector to get rid of spurs and strong interfering signals. I'll dig out the plugs tonite and see what I find. Maybe I'll get lucky and one will fix itself. Incidentally, the mixer likes to blow up in the hp8555a when you transmit into it. The fix: http://www.k3pgp.org/hp8555a.htm I feel like you getting even for the MFJ1800 :-) I've thought about that. Please inspect any packages you receive from me with a bomb sniffer before opening. I have a 300Mhz scope, just to complicate things. Measured 7.5Vpp. Sooo, I get 0.143 watts, so much for spec's. I was going to suggest you try a 75 ohm load, but it looks like the xmitter is specified at 50 ohms. http://www.elecsky.com http://www.czhfm.com/datasheet/CZH-05B-Manual.pdf Looks like the rubber ducky is tuned to the FM band. http://www.elecsky.com/index.php?main_page=product_info&cPath=10&products _id=5 If I install the rubber ducky in place of the 50 ohm, I get 8.3Vpp. If you run it open load, you'll probably see even more voltage. The power measurement is only valid with a proper 50 ohm dummy load or 50 ohm antenna. Later, I'll connect my MFJ259 to the rubber ducky, and see what it says. The display will probably say "give up and get a real antenna". Ya, maybe, but I'm running low power through 6db of attenuation with two walls and an aluminum screened porch between my problem area and the transmitter. Now you tell me. Perhaps all the junk in the way might have an effect on the signal level? Instead of a new antenna, perhaps moving the transmitter or running a longer coax run might be useful? Minor problems, like I say I can move the radio 5ft and solve the problem. Too easy. Moving the radio or antenna does not demonstrate how they work. Without suffering there can be no enlightenment. I just turn up the volume control to get the same effect. The neighbors would think I'm weird, I listen to Science 360, Gunsmoke, Phil Hendrie, what a train wreck! Yeah, you have a problem. Perhaps if you play what the neighbors prefer to hear, they might be more tolerant of your bizarre listening habits. My usual mix is 60's electric acid rock, New Age, and classical music. I haven't determined if this is the result of brain damage, or the cause. Need to go take over for my wife at the business, I'll reread what you said here and look at links when I get to work, it's a tough job (well, not really) but somebodies got to do it. Bah Humbug (T'is the season to be grumpy). -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Turning a 1/4 wave vertical upside down
On 12/1/2013 2:42 PM, amdx wrote:
On 12/1/2013 11:48 AM, Irv Finkleman wrote: Before too much theorizing takes place, why not try just placing it in a convenient location in the house -- you might be pleasantly surprised. If that doesn't work, then, and only then, it becomes a technical problem. Irv VE6BP That's good advice, except I have three different audio inputs that all land where I now have the transmitter. Besides, we like technical problems! :-) After my last response to Jeff when I measured the output voltage, I just realized I can check the loss through the LPF. Hot dog! Can't wait to get home. Mikek Don't fool yourself. A 10x probe has maybe 10pF capacitance. What is that reactance at 100MHz? About maybe 160 ohms? How will that affect your measurement? As far as an upside down vertical is concerned, you should get the free copy of EZNEC and study what it is that you want to achieve. The ground characteristics and the height above it is what determines the so-called angle of max radiation. Height alone is sufficient to lower the angle. For example, a perfectly conducting earth has an angle of maximum radiation of zero degrees. Think about it. |
Turning a 1/4 wave vertical upside down
"amdx" wrote in message ... The receive area is small, 120" x 115", the antenna will be mounted 13" in from the long dimension and 16" in from the smaller dimension, basically in the corner of the lot, mounted 16 ft high. Jeff, at this point, I have convinced myself putting a gain antenna on the roof will solve any problem I may have. If not I can still remove 6db of attenuation. So unless you want some mental exercise, don't over do it! I am sure you mean feet ' instead of inches ". Without doing the math, I would think that 150 feet would be the most you would need out of the system. What is wrong with a horizontal dipole ? It should cover the area just fine, and if not take out those attuenuators. I am not up on all the part 15 rules, but I was thinking 100 milliwatts was fine to run. If you can't hear it 200 feet away, I doubt the FCC is going to worry about it with all the other things they have going on. Could that buzzing noise you hear be some other signal such as cable leakage or the AC power lines line noise ? |
Turning a 1/4 wave vertical upside down
On 12/1/2013 5:17 PM, John S wrote:
On 12/1/2013 2:42 PM, amdx wrote: On 12/1/2013 11:48 AM, Irv Finkleman wrote: Before too much theorizing takes place, why not try just placing it in a convenient location in the house -- you might be pleasantly surprised. If that doesn't work, then, and only then, it becomes a technical problem. Irv VE6BP That's good advice, except I have three different audio inputs that all land where I now have the transmitter. Besides, we like technical problems! :-) After my last response to Jeff when I measured the output voltage, I just realized I can check the loss through the LPF. Hot dog! Can't wait to get home. Mikek Don't fool yourself. A 10x probe has maybe 10pF capacitance. What is that reactance at 100MHz? About maybe 160 ohms? How will that affect your measurement? I don't know. I put a T on the scope with 50 ohms on one side and the transmitter driving the other side. The scope is 15pf/1Meg input impedance. Two of the measurements I made a 50 ohms or antenna and with 110Mhz LPF and without LPF. Transmitter at 87.5Mhz 50 ohm 7.33Vpp l Transmitter---LPF---l l scope 50 ohm 7.13Vpp l Transmitter---------l l scope I don't know how the 15pf affects this measurement. But I don't see much loss in my LPF. Rubber Ducky 8.45Vpp l Transmitter---LPF---l l scope Rubber Ducky 8.45Vpp l Transmitter---------l l scope I checked this twice, I have digital voltage display on the scope. So no loss at transmit frequency. I don't know how that works, I'll be checking for radiation soon! Is there anyway to compensate for the 15pf, could I put an equivalent inductance in the scope input circuit? (for this frequency only) I have two 3db attenuators, when I put those between the transmitter and the LPF and the LPF and the Load (antenna/50 ohms) I get slightly less loss with the 50 ohm load and slightly more loss with the antenna. What say you? Thanks, Mikek PS. I want to check the attenuation of the LPF at 175 Mhz and 262.5. I just threw away a QST that had an article with a 220Mhz osc. I'll retrieve that tomorrow. |
Turning a 1/4 wave vertical upside down
On 12/1/2013 6:21 PM, Ralph Mowery wrote:
"amdx" wrote in message ... The receive area is small, 120" x 115", the antenna will be mounted 13" in from the long dimension and 16" in from the smaller dimension, basically in the corner of the lot, mounted 16 ft high. Jeff, at this point, I have convinced myself putting a gain antenna on the roof will solve any problem I may have. If not I can still remove 6db of attenuation. So unless you want some mental exercise, don't over do it! I am sure you mean feet ' instead of inches ". Without doing the math, I would think that 150 feet would be the most you would need out of the system. What is wrong with a horizontal dipole ? It should cover the area just fine, and if not take out those attuenuators. I am not up on all the part 15 rules, but I was thinking 100 milliwatts was fine to run. If you can't hear it 200 feet away, I doubt the FCC is going to worry about it with all the other things they have going on. I don't think so either, I just want to do the job with minimum power. Now that I've messed with the new 110 Mhz filter a bit, I might remove one 3 db attenuator and see how it works around the yard. Could that buzzing noise you hear be some other signal such as cable leakage or the AC power lines line noise ? I think it's 60 hertz or a harmonic, but with enough RF, I don't think I'd hear it. It seemed better, after I added my LPF, I don't think because of the filtering but maybe impedance changes. Mikek |
Turning a 1/4 wave vertical upside down
On 12/1/2013 7:17 PM, amdx wrote:
On 12/1/2013 5:17 PM, John S wrote: On 12/1/2013 2:42 PM, amdx wrote: On 12/1/2013 11:48 AM, Irv Finkleman wrote: Before too much theorizing takes place, why not try just placing it in a convenient location in the house -- you might be pleasantly surprised. If that doesn't work, then, and only then, it becomes a technical problem. Irv VE6BP That's good advice, except I have three different audio inputs that all land where I now have the transmitter. Besides, we like technical problems! :-) After my last response to Jeff when I measured the output voltage, I just realized I can check the loss through the LPF. Hot dog! Can't wait to get home. Mikek Don't fool yourself. A 10x probe has maybe 10pF capacitance. What is that reactance at 100MHz? About maybe 160 ohms? How will that affect your measurement? I don't know. If you can't calculate or reason out the answer, then you need a teacher better than I. |
Turning a 1/4 wave vertical upside down
On Sun, 1 Dec 2013 19:21:19 -0500, "Ralph Mowery"
wrote: Could that buzzing noise you hear be some other signal such as cable leakage or the AC power lines line noise ? Trivia: Cable leakage has changed over the last few years. The sync buzz of the analog TV era has been replaced by digital hiss. Put a temporary antenna on your cable connection and listen on a suitable receiver. Some cable systems still carry FM broadcast stations, so he might also be hearing those coming from a cable leak. Locally, everything was moved to digital channels in 2005. http://www.sfgate.com/business/article/Comcast-to-restore-30-FM-radio-stations-Some-2625920.php "Any sufficiently advanced communications technology is indistiguishable from noise" (appologies to Arthur C. Clarke). -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Turning a 1/4 wave vertical upside down
"Jeff Liebermann" wrote in message Trivia: Cable leakage has changed over the last few years. The sync buzz of the analog TV era has been replaced by digital hiss. Put a temporary antenna on your cable connection and listen on a suitable receiver. Some cable systems still carry FM broadcast stations, so he might also be hearing those coming from a cable leak. Locally, everything was moved to digital channels in 2005. http://www.sfgate.com/business/article/Comcast-to-restore-30-FM-radio-stations-Some-2625920.php I guess it depends on where you are Jeff. Around where I live there about 100 channels that are still analog. Still starting at the old channel 2. The state I live in is still way behind times. |
Turning a 1/4 wave vertical upside down
On Mon, 2 Dec 2013 00:00:37 -0500, "Ralph Mowery"
wrote: "Jeff Liebermann" wrote in message Trivia: Cable leakage has changed over the last few years. The sync buzz of the analog TV era has been replaced by digital hiss. Put a temporary antenna on your cable connection and listen on a suitable receiver. Some cable systems still carry FM broadcast stations, so he might also be hearing those coming from a cable leak. Locally, everything was moved to digital channels in 2005. http://www.sfgate.com/business/article/Comcast-to-restore-30-FM-radio-stations-Some-2625920.php I guess it depends on where you are Jeff. Around where I live there about 100 channels that are still analog. Still starting at the old channel 2. Comcast is now all digital in the People's Republic of Santa Cruz CA. Of course Comcast has a new scam. You get up to two "free" DTA boxes: http://customer.comcast.com/Pages/FAQViewer.aspx?seoid=What-is-a-digital-adapter for listening to FM and viewing non-HD channels. It was originally announced that it was "free" for 2 years, but Comcast started adding $5/month per box to some peoples bills in about June. One problem is that the DTA box somehow manages to produce worse than analog quality TV pictures. Digital in, garbage out. I don't know how they managed it, but the "free" box produces some of the worst looking pictures I have ever seen since the introduction of color TV. The Comcast solution is to rent a similar box, that produces HD video, and amazingly produces decent looking non-HD video for $10/month. That's $120/year per TV set for what used to be free: http://bgr.com/2013/10/16/comcast-digital-adapter-criticism/ https://www.google.com/search?q=comcast+dta&tbm=isch Oddly, both types of DTA boxes use the same digital data for non-HD stations, so it's not Comcast that's sending garbage video. It's the DTA box. Both types of boxes will play some local FM stations, but I've only tried it on the HD version. Works fine but will vary by area. For Santa Cruz, we get about 30 stations. The state I live in is still way behind times. That may not be such a bad thing. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Turning a 1/4 wave vertical upside down
"Jeff Liebermann" wrote in message ... Comcast is now all digital in the People's Republic of Santa Cruz CA. Of course Comcast has a new scam. You get up to two "free" DTA boxes: http://customer.comcast.com/Pages/FAQViewer.aspx?seoid=What-is-a-digital-adapter for listening to FM and viewing non-HD channels. It was originally announced that it was "free" for 2 years, but Comcast started adding $5/month per box to some peoples bills in about June. One problem is that the DTA box somehow manages to produce worse than analog quality TV pictures. Digital in, garbage out. I don't know how they managed it, but the "free" box produces some of the worst looking pictures I have ever seen since the introduction of color TV. The Comcast solution is to rent a similar box, that produces HD video, and amazingly produces decent looking non-HD video for $10/month. That's $120/year per TV set for what used to be free: http://bgr.com/2013/10/16/comcast-digital-adapter-criticism/ https://www.google.com/search?q=comcast+dta&tbm=isch Oddly, both types of DTA boxes use the same digital data for non-HD stations, so it's not Comcast that's sending garbage video. It's the DTA box. I have an old cable ready TV that gets close to 100 of the analog chanels. Just to see if it would work, I hooked up one of the off the air digital converter boxes up to the cable an it did not pick up anything. Guess that lets that out if our area goes to all digital. A newer TV gets the analog and digital chanels off the cable. Then I have one of the boxes hooked to the main TV.. If my wife could operate things, I would go to something like Netflix. The box does work off the air and I get about 30 chanels off the air with an antenna out side the house. |
Quote:
In practice, at such close range, it matters little how you mount your antenna. As such a rubber ducky would be good enough. 73, Nandu http://nandustips.blogspot.com |
Turning a 1/4 wave vertical upside down
On Tue, 3 Dec 2013 23:37:43 -0500, "Ralph Mowery"
wrote: A newer TV gets the analog and digital chanels off the cable. Then I have one of the boxes hooked to the main TV.. If my wife could operate things, I would go to something like Netflix. For Netflix, there are a variety of options. Computer, game box, media player, tablet computers, and built into the TV. For your wife, I suggest you try one of the Roku media players: http://www.roku.com/products/compare I have an older Roku 2 XS box and use it for Netflix. The remote control has only a few buttons, so it's fairly easy to learn. The difficult part is searching for shows to watch. I like to do that on a computah, where I can type in the name of the program on a real keyboard. You can plug in a keyboard into the Roku box, but that might add too much complexity. When I find something worth watching, I add it to my "favorites" list, which appears at the top of the screen when selecting shows on Netflix. What's really nice about Netflix is the total lack of commercials. Last week, one of my customers bought an Xbox One gizmo at Costco. Nifty system which can be voice controlled. All he has to do is say "Xbox show Netflix" and it's up. However, within Netflix, he has to use the included remote control. With the cable box, he can go directly to his favorite channel. "Xbox show TCM" will bring up Turner Classic Movies. If your wife can handle voice commands, it might be an (expensive) option. Marginally related RF drivel: One of my friends is avid DX'er. He has all his media and computer gizmos interconnected via Wi-Fi because Wi-Fi creates less RFI than ethernet. Then, he asks me to figure out why his wi-fi is so slow. None of the computers caused problems, but running Netflix in full 1080p was what was killing his wireless. My solution was to sell him a dual band wireless router, and reserve the 5GHz band for video. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Turning a 1/4 wave vertical upside down
On 12/16/2013 2:43 AM, Jeff Liebermann wrote:
On Tue, 3 Dec 2013 23:37:43 -0500, "Ralph Mowery" wrote: A newer TV gets the analog and digital chanels off the cable. Then I have one of the boxes hooked to the main TV.. If my wife could operate things, I would go to something like Netflix. For Netflix, there are a variety of options. Computer, game box, media player, tablet computers, and built into the TV. For your wife, I suggest you try one of the Roku media players: http://www.roku.com/products/compare I have an older Roku 2 XS box and use it for Netflix. The remote control has only a few buttons, so it's fairly easy to learn. The difficult part is searching for shows to watch. I like to do that on a computah, where I can type in the name of the program on a real keyboard. You can plug in a keyboard into the Roku box, but that might add too much complexity. When I find something worth watching, I add it to my "favorites" list, which appears at the top of the screen when selecting shows on Netflix. What's really nice about Netflix is the total lack of commercials. Last week, one of my customers bought an Xbox One gizmo at Costco. Nifty system which can be voice controlled. All he has to do is say "Xbox show Netflix" and it's up. However, within Netflix, he has to use the included remote control. With the cable box, he can go directly to his favorite channel. "Xbox show TCM" will bring up Turner Classic Movies. If your wife can handle voice commands, it might be an (expensive) option. Marginally related RF drivel: One of my friends is avid DX'er. He has all his media and computer gizmos interconnected via Wi-Fi because Wi-Fi creates less RFI than ethernet. Then, he asks me to figure out why his wi-fi is so slow. None of the computers caused problems, but running Netflix in full 1080p was what was killing his wireless. My solution was to sell him a dual band wireless router, and reserve the 5GHz band for video. Then he has a problem in his ethernet. Properly installed, ethernet creates virtually no interference. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
This post sound a lot more like one person thinking out loud, or two people having a conversation in such a way that they are trying to teach something - a lot like a infomertial.
The bottom line is - who cares. .1 watt or 1 watt - the antenna the OP showed is either for 400 something Mhz or 900 mhz. Until the neighbors complains - you can do what ever you want. A local ham once told the story of a neighbor that had a baby monitor that operated on 50 something MHz. To this ham - 6 meters was sacred. To have to listen to some screaming baby day and night was intolerable. Especially since these people lived on Mt Morenci road near Ridgeway PA and the elevation there reaches somewhere near 1900', the average terrain being only about 1400' - the baby monitor acted a lot like a 50 watt transmitter because of the height gain. When they complained to the owner of the baby monitor, those people just laughed and said that it was a problem that the manufacturer should address, not the owner. So the hams made some tapes of the couple making love - which came over the baby monitor loud and clear each night and passed them around the community. It wasn't very long after the couple found out that they were going viral that they got rid of the baby monitor. The output of the transmitter has a lot less to do with the range of the transmitter then does the location and size of the antenna. the problem being that if the radio transmitter was 400 mhz you would have some loss in the coax between the transmitter and the antenna that would negate any gains to be had by putting the antenna higher or outside. If the radio transmitter was 900 mhz, now you have a big problem - where the loss in the coax is so great if the coax is more then a couple of feet long that any gains you could have are lost in the coax and unless you properly match the coax, the heating it might cause inside of the cheap $50 transmitter might be enough to burn it up. Hence if the transmitters frequency is high enough, it will solve its own problem.. A FM broadcast transmitter in the range of 88 - 107 Mhz wouldn't really matter. I guess this is the point that I am making. I have read several articles of night clubs - especially around the Cleveland Ohio that took it upon themselves to modify a FM transmitter that would normally have a range of about 1000' and modify it so it could be heard 20 miles away. When the complaints were registered by the legal owners of the frequency, the FCC stepped in and removed the transmitter and gave the owners of the club a big fine. A month later a even bigger transmitter was found on the premises and another fine was levied. Two months after that, another transmitter was found on the property - which leads me to believe that the transmitter that the FCC found was the one that the club wanted them to find. The second transmitter was an alternate transmitter and the third transmitter was the actual transmitter. By the third fine, there was no way that a club - even in Cleveland Ohio could take in more legal revenue then it was paying out in fines. Oh and did i MENTION -the dancers wore no clothes. |
Turning a 1/4 wave vertical upside down
On Mon, 16 Dec 2013 14:27:54 +0000, Channel Jumper
wrote: This post sound a lot more like one person thinking out loud, or two people having a conversation in such a way that they are trying to teach something - a lot like a infomertial. Well, you're back to your standard template. You begin all your replies with a personal insult and follow it with drivel that has nothing to do with the topic under discussion. Well, there was one posting where you omitted the opening volly, after I suggested that you drop it. In case you missed it, the topic is whether a low power FM transmitter coverage will benefit from mounting the antenna upside down. The bottom line is - who cares. Correct. NBC (nobody cares). -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Turning a 1/4 wave vertical upside down
On Mon, 16 Dec 2013 07:46:16 -0500, Jerry Stuckle
wrote: Then he has a problem in his ethernet. Properly installed, ethernet creates virtually no interference. Yes, that's the theory. If the cable isn't perfectly balanced, it will become an antenna. Shielded ethernet adds additional opportunities to radiate. Most of the RFI originates from ethernet switches and routers. One oddity are ethernet hubs. What goes in one port, goes out all the other ports. With a switch, only data destined for a specific MAC address on another port is passed. The problem is many older hubs will send data to a port if a cable is inserted but not terminated. They're not suppose to do that, but I've found a few old hubs that do that. If you have an ethernet RFI problem, look into replacing hubs with switches. "Understanding and Eliminating RF Interference" by Jim Brown K9YC http://www.audiosystemsgroup.com/RFIHamNCCC.pdf Start reading at Page 20 for the ethernet radiation section. Mo http://www.audiosystemsgroup.com/publish.htm This thread may also be of interest: http://lists.contesting.com/_rfi/2008-11/msg00025.html Note that 100baseT is quieter than 10baseT. With 100baseT, the data is first 4B5B encoded at 125Mbits/sec. To reduce crosstalk, it is then scrambled and MLT-3 encoded. The result is a 31.2MHz carrier and a mess of sidebands. The necessary scrambling has the side effect of reducing high power peaks, and evening out the power spectrum over a wider frequency range, thus reducing the RFI power at any given frequency. It's much the same idea as the "spread spectrum" modulation of computer clocks, to spread the power over a wider frequency range, to meet FCC Part 15 requirements. So, instead of a carrier or birdie, you'll hear broadband noise, which I guess is more tolerable. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Turning a 1/4 wave vertical upside down
On 12/16/2013 12:54 PM, Jeff Liebermann wrote:
On Mon, 16 Dec 2013 07:46:16 -0500, Jerry Stuckle wrote: Then he has a problem in his ethernet. Properly installed, ethernet creates virtually no interference. Yes, that's the theory. If the cable isn't perfectly balanced, it will become an antenna. Shielded ethernet adds additional opportunities to radiate. Most of the RFI originates from ethernet switches and routers. It's more than just theory. Over the years, we've installed hundreds of ethernet systems, with little or no interference. Shielded Category cable is much better - but you need to be careful. It needs to be grounded at one end only (to prevent ground loops), and the shield must carry through to the devices at the far end. The devices must be shielded also, preferably in metal cases. Unfortunately, most consumer-grade devices have plastic cases with little or no shielding and do not connect to the shield. In cases like this, yes, the shield can become a radiator. Commercial devices are better at this (but are a lot more expensive). One oddity are ethernet hubs. What goes in one port, goes out all the other ports. With a switch, only data destined for a specific MAC address on another port is passed. The problem is many older hubs will send data to a port if a cable is inserted but not terminated. They're not suppose to do that, but I've found a few old hubs that do that. If you have an ethernet RFI problem, look into replacing hubs with switches. Again, that's the case with consumer-grade goods. Commercial grade are much better at this. "Understanding and Eliminating RF Interference" by Jim Brown K9YC http://www.audiosystemsgroup.com/RFIHamNCCC.pdf Start reading at Page 20 for the ethernet radiation section. Mo http://www.audiosystemsgroup.com/publish.htm I think our expertise of doing this as a business for years in both residential and commercial establishments qualifies us. This thread may also be of interest: http://lists.contesting.com/_rfi/2008-11/msg00025.html Note that 100baseT is quieter than 10baseT. With 100baseT, the data is first 4B5B encoded at 125Mbits/sec. To reduce crosstalk, it is then scrambled and MLT-3 encoded. The result is a 31.2MHz carrier and a mess of sidebands. The necessary scrambling has the side effect of reducing high power peaks, and evening out the power spectrum over a wider frequency range, thus reducing the RFI power at any given frequency. It's much the same idea as the "spread spectrum" modulation of computer clocks, to spread the power over a wider frequency range, to meet FCC Part 15 requirements. So, instead of a carrier or birdie, you'll hear broadband noise, which I guess is more tolerable. Again, it depends on the installation and equipment being used. But 10baseT is also old technology. 100baseT is more recent and solves a lot of problems - both in radiation and susceptibility to interference from external radiation. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
Turning a 1/4 wave vertical upside down
On Sun, 15 Dec 2013 23:43:26 -0800 in rec.radio.amateur.antenna,
Jeff Liebermann wrote, Marginally related RF drivel: One of my friends is avid DX'er. He has all his media and computer gizmos interconnected via Wi-Fi because Wi-Fi creates less RFI than ethernet. Woah, how can that be? Would using shielded cat6 fix it? |
Turning a 1/4 wave vertical upside down
On 12/16/2013 8:27 AM, Channel Jumper wrote:
1 watt or 1 watt - the antenna the OP showed is either for 400 something Mhz or 900 mhz. What's your point? Mikek |
Turning a 1/4 wave vertical upside down
On 12/16/2013 11:11 AM, Jeff Liebermann wrote:
On Mon, 16 Dec 2013 14:27:54 +0000, Channel Jumper wrote: This post sound a lot more like one person thinking out loud, or two people having a conversation in such a way that they are trying to teach something - a lot like a infomertial. Well, you're back to your standard template. You begin all your replies with a personal insult and follow it with drivel that has nothing to do with the topic under discussion. Well, there was one posting where you omitted the opening volly, after I suggested that you drop it. In case you missed it, the topic is whether a low power FM transmitter coverage will benefit from mounting the antenna upside down. The bottom line is - who cares. Correct. NBC (nobody cares). Well, I did :-) But I'm not nobody! Two reasons, if it gave my a better coverage pattern for my yard, I would do it. Second reason, I'm curious, and you did answer my question with an example. Thanks. Anyway, moved the antenna a few feet, installed my filter, removed one 3db attenuator, and ran around the yard with my radio and didn't notice any problem. It even got better reception in my workshop not perfect, but better. Mikek |
Turning a 1/4 wave vertical upside down
On 12/2/2013 12:39 AM, Jeff Liebermann wrote:
Comcast is now all digital in the People's Republic of Santa Cruz CA. I got my cable bill a few days ago, noted it had increased $10.00. Told the wife, she said ya, after Nov. the reduction I got last Nov. expired. She went in, made her yearly complaint, but this time she got a $20.00 discount! The bill dropped from $123.54 to $103.xx. (Cable, phone and internet) $240 a year, I think I'll taker her out for an ice cream cone. :-) Mikek |
Turning a 1/4 wave vertical upside down
On Mon, 16 Dec 2013 13:42:54 -0500, Jerry Stuckle
wrote: On 12/16/2013 12:54 PM, Jeff Liebermann wrote: On Mon, 16 Dec 2013 07:46:16 -0500, Jerry Stuckle wrote: Then he has a problem in his ethernet. Properly installed, ethernet creates virtually no interference. Yes, that's the theory. If the cable isn't perfectly balanced, it will become an antenna. Shielded ethernet adds additional opportunities to radiate. Most of the RFI originates from ethernet switches and routers. It's more than just theory. Over the years, we've installed hundreds of ethernet systems, with little or no interference. Ummm... you check for RFI problems on hundreds of ethernet installations? Perhaps I missed that section in the BICSI certification guides. I don't recall any requirement to test for excessive radiation, though it probably wouldn't be a bad idea. Good to see that someone is conscientious about ethernet RFI. (Full Disclosu I'm not certified but have skimmed the material). The only time I check for radiation is when I install something for hams. I have a cute little Alinco DJ-X2 HF receiver for sniffing, but mostly it's just checking with the owners HF radio. Mostly, what I find is noise originating from the wall warts and power supplies. The switcher types are awful. I also find some rather noisy LED lighting, plasma TV's, and computers. Once those are eliminated, the rest of the noise is conducted by the ethernet wiring. I usually bring an assortment of big ferrite beads with me to deal with those. Shielded Category cable is much better - but you need to be careful. It needs to be grounded at one end only (to prevent ground loops), and the shield must carry through to the devices at the far end. Agreed. Some countries (Switzerland) insist that all CAT5 be shielded. Too bad that all of the pre-made shielded cables have shield connections on both ends with no way to break the connection. If you ground the source end of the cable, you end up with an antenna and no shielding. Since ethernet has sources at both ends of the cable, you have to ground both ends to get decent shielding. See conclusions on Pg 31. http://dallasemc.org/2010-10EMItroubleshooting.pdf (Pages 26 thru 31 for ethernet). The devices must be shielded also, preferably in metal cases. Unfortunately, most consumer-grade devices have plastic cases with little or no shielding and do not connect to the shield. In cases like this, yes, the shield can become a radiator. Commercial devices are better at this (but are a lot more expensive). Most of the 16, 24, and 48 port switches that I use are in metal boxes. With all the RFI they generated, a shielded box is required to pass FCC Part 15. Lately, I'm seeing "green" ethernet switches, reduce power depending on CAT5 length. http://www.dlinkgreen.com/energyefficiency.asp Hopefully, that will reduce radiation by simply lowering transmit power. I find the consumer grade plastic boxes are tolerable. Some (i.e. Linksys) have decent grounding systems. Others have internal shields. However, I believe that cable shields are detrimental rather than beneficial. The ability of the CAT5 cable to NOT radiate junk is dependent on the balance between each wire in a twisted pair. If anything unbalances the twisted pair, the CMMR is ruined, and the wires radiate. (Reminder... wires radiate, components do not). Having 3 extra pairs of wires rubbing up against a pair of wires in the bundle is bad enough for balance. In some CAT6 cables, a cross shaped insulator runs down the length of the cable to keep the pairs separated. However, if we add a shield, the capacitance between each wire of a pair can be different depending on the spacing from the shield. The change is not much, but sufficient to produce enough unbalance for the pair to radiate. You can see the problem with a length of shielded CAT5 and a capacitance meter. Measure the capacitance from each wire in a pair to the shield. It may vary some fraction of a PF, but that's enough to unbalance the pair and produce some radiation. Also, note that it's not necessary for one wire out of twisted pair to do the radiating. The RFI could easily be radiated by wires from an adjacent pair if they were sufficiently well coupled. One oddity are ethernet hubs. What goes in one port, goes out all the other ports. With a switch, only data destined for a specific MAC address on another port is passed. The problem is many older hubs will send data to a port if a cable is inserted but not terminated. They're not suppose to do that, but I've found a few old hubs that do that. If you have an ethernet RFI problem, look into replacing hubs with switches. Again, that's the case with consumer-grade goods. Commercial grade are much better at this. I beg to differ. Hubs (repeaters) are quite different from switches (multiport bridges) in operation. The problem is that the hubs will transmit into a CAT5 cable with nothing at the other end. Common mode rejection on the pair will prevent it from radiating. However, the high VSWR caused by the lack of a termination, might cause it to radiate. "Understanding and Eliminating RF Interference" by Jim Brown K9YC http://www.audiosystemsgroup.com/RFIHamNCCC.pdf Start reading at Page 20 for the ethernet radiation section. Mo http://www.audiosystemsgroup.com/publish.htm I think our expertise of doing this as a business for years in both residential and commercial establishments qualifies us. With all due respect, that sounds like bluster. You may very well have had hundreds of successful installations, but I question if they were all tested for RFI. This thread may also be of interest: http://lists.contesting.com/_rfi/2008-11/msg00025.html Note that 100baseT is quieter than 10baseT. With 100baseT, the data is first 4B5B encoded at 125Mbits/sec. To reduce crosstalk, it is then scrambled and MLT-3 encoded. The result is a 31.2MHz carrier and a mess of sidebands. The necessary scrambling has the side effect of reducing high power peaks, and evening out the power spectrum over a wider frequency range, thus reducing the RFI power at any given frequency. It's much the same idea as the "spread spectrum" modulation of computer clocks, to spread the power over a wider frequency range, to meet FCC Part 15 requirements. So, instead of a carrier or birdie, you'll hear broadband noise, which I guess is more tolerable. Again, it depends on the installation and equipment being used. But 10baseT is also old technology. 100baseT is more recent and solves a lot of problems - both in radiation and susceptibility to interference from external radiation. Agreed. Things do depend on the equipment and installation. Personally, I only do quality installations and use only the best equipment. For example: http://www.LearnByDestroying.com/jeffl/pics/drivel/slides/mess01.html I've seen worse, but the owners didn't want me posting photos. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Turning a 1/4 wave vertical upside down
On Mon, 16 Dec 2013 11:21:30 -0800, David Harmon
wrote: On Sun, 15 Dec 2013 23:43:26 -0800 in rec.radio.amateur.antenna, Jeff Liebermann wrote, Marginally related RF drivel: One of my friends is avid DX'er. He has all his media and computer gizmos interconnected via Wi-Fi because Wi-Fi creates less RFI than ethernet. Woah, how can that be? Would using shielded cat6 fix it? I don't know. I don't have much experience with CAT6 STP as most of my installations use CAT5e UTP cable (including for gigabit). It might reduce radiation by shielding, or increase it if there's a ground loop. In any case, the owner was not interested in wiring the house, station, garage, antenna farm, front gate, home theater, etc for ethernet. Wi-Fi did the job well enough and did not product RFI. In retrospect, I probably should have spent more time finding the exact sources of the HF interference. I did not make a systematic check of the house, and did not check everything electrical in the house. I didn't have the time as that would have taken days. Instead, there was a large drop in RFI observed when the ethernet connected devices were unplugged, so we went with that. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Turning a 1/4 wave vertical upside down
On Mon, 16 Dec 2013 14:27:17 -0600, amdx wrote:
On 12/2/2013 12:39 AM, Jeff Liebermann wrote: Comcast is now all digital in the People's Republic of Santa Cruz CA. I got my cable bill a few days ago, noted it had increased $10.00. Told the wife, she said ya, after Nov. the reduction I got last Nov. expired. She went in, made her yearly complaint, but this time she got a $20.00 discount! The bill dropped from $123.54 to $103.xx. (Cable, phone and internet) $240 a year, I think I'll taker her out for an ice cream cone. :-) Mikek Nice, but you can do better than giving her just an ice cream cone. Do I get an ice cream cone if I suggest you drop the cable TV and phone, and leave the internet. Then, switch to a VoIP provider and watch IPTV via Netflix and such? My guess price is: Comcast internet $50/month for first 12 months Comcast internet $80/month after first 12 months Future-Nine America Free $13.50/month Netflix $8/month Roku 3 media player $90 SIP phone (SPA941) $80 Send the ice cream to the address below. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Turning a 1/4 wave vertical upside down
On Mon, 16 Dec 2013 19:25:12 -0800, Jeff Liebermann
wrote: If you ground the source end of the cable, you end up with an antenna and no shielding. Since ethernet has sources at both ends of the cable, you have to ground both ends to get decent shielding. See conclusions on Pg 31. http://dallasemc.org/2010-10EMItroubleshooting.pdf (Pages 26 thru 31 for ethernet). Oops. That should be "If you don't ground the source end of the cable..." -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Turning a 1/4 wave vertical upside down
On 12/16/2013 10:25 PM, Jeff Liebermann wrote:
On Mon, 16 Dec 2013 13:42:54 -0500, Jerry Stuckle wrote: On 12/16/2013 12:54 PM, Jeff Liebermann wrote: On Mon, 16 Dec 2013 07:46:16 -0500, Jerry Stuckle wrote: Then he has a problem in his ethernet. Properly installed, ethernet creates virtually no interference. Yes, that's the theory. If the cable isn't perfectly balanced, it will become an antenna. Shielded ethernet adds additional opportunities to radiate. Most of the RFI originates from ethernet switches and routers. It's more than just theory. Over the years, we've installed hundreds of ethernet systems, with little or no interference. Ummm... you check for RFI problems on hundreds of ethernet installations? Perhaps I missed that section in the BICSI certification guides. I don't recall any requirement to test for excessive radiation, though it probably wouldn't be a bad idea. Good to see that someone is conscientious about ethernet RFI. (Full Disclosu I'm not certified but have skimmed the material). Where it's necessary, yes. And in most commercial installations, it is necessary. It really doesn't take long, unless it's a huge install. And no, it isn't part of the BICSI guidelines - but they also aren't the bottom line in certifications (although they would like to think they are). The only time I check for radiation is when I install something for hams. I have a cute little Alinco DJ-X2 HF receiver for sniffing, but mostly it's just checking with the owners HF radio. Mostly, what I find is noise originating from the wall warts and power supplies. The switcher types are awful. I also find some rather noisy LED lighting, plasma TV's, and computers. Once those are eliminated, the rest of the noise is conducted by the ethernet wiring. I usually bring an assortment of big ferrite beads with me to deal with those. As I said - many commercial installations need it, also. Shielded Category cable is much better - but you need to be careful. It needs to be grounded at one end only (to prevent ground loops), and the shield must carry through to the devices at the far end. Agreed. Some countries (Switzerland) insist that all CAT5 be shielded. Too bad that all of the pre-made shielded cables have shield connections on both ends with no way to break the connection. If you ground the source end of the cable, you end up with an antenna and no shielding. Since ethernet has sources at both ends of the cable, you have to ground both ends to get decent shielding. See conclusions on Pg 31. http://dallasemc.org/2010-10EMItroubleshooting.pdf (Pages 26 thru 31 for ethernet). No, you do not end up with an antenna if you ground only the source end. But grounding it at both ends creates a ground loop. This was a recognized problem even back in the 70's, when I was working for IBM and we had video terminals on the ends of up to 3000 ft. of coax. I think you are missing the point here. Terminating the shield at both ends is not the same as grounding the shield at both ends. The devices must be shielded also, preferably in metal cases. Unfortunately, most consumer-grade devices have plastic cases with little or no shielding and do not connect to the shield. In cases like this, yes, the shield can become a radiator. Commercial devices are better at this (but are a lot more expensive). Most of the 16, 24, and 48 port switches that I use are in metal boxes. With all the RFI they generated, a shielded box is required to pass FCC Part 15. Lately, I'm seeing "green" ethernet switches, reduce power depending on CAT5 length. http://www.dlinkgreen.com/energyefficiency.asp Hopefully, that will reduce radiation by simply lowering transmit power. All items which generate rf (which includes basically anything with digital signals) must pass FCC Part 15. But there are two sections in Part 15 - Part A (residential) and Part B (commercial), Part A is more stringent, but you will notice that most devices are Part B certified. But that also does not mean they will not cause interference; it only means the interference they cause is within certain limits. I find the consumer grade plastic boxes are tolerable. Some (i.e. Linksys) have decent grounding systems. Others have internal shields. However, I believe that cable shields are detrimental rather than beneficial. The ability of the CAT5 cable to NOT radiate junk is dependent on the balance between each wire in a twisted pair. If anything unbalances the twisted pair, the CMMR is ruined, and the wires radiate. (Reminder... wires radiate, components do not). Having 3 extra pairs of wires rubbing up against a pair of wires in the bundle is bad enough for balance. In some CAT6 cables, a cross shaped insulator runs down the length of the cable to keep the pairs separated. However, if we add a shield, the capacitance between each wire of a pair can be different depending on the spacing from the shield. The change is not much, but sufficient to produce enough unbalance for the pair to radiate. You can see the problem with a length of shielded CAT5 and a capacitance meter. Measure the capacitance from each wire in a pair to the shield. It may vary some fraction of a PF, but that's enough to unbalance the pair and produce some radiation. Also, note that it's not necessary for one wire out of twisted pair to do the radiating. The RFI could easily be radiated by wires from an adjacent pair if they were sufficiently well coupled. You can believe all you want. But my experience is much different. For instance, the presence of a shield actually improves balance in the wires; the way wires are twisted in a pair averages the distance to the shield to be the same. A fraction of a pf is not going to significantly unbalance anything - nothing is perfect, anyway. However, when running a cable, bringing it near anything metal (even nails in the wall) can unbalance unshielded category cable, while shielded category cable minimizes the effects of external metal. And different pairs have different twists to limit coupling between wires. One oddity are ethernet hubs. What goes in one port, goes out all the other ports. With a switch, only data destined for a specific MAC address on another port is passed. The problem is many older hubs will send data to a port if a cable is inserted but not terminated. They're not suppose to do that, but I've found a few old hubs that do that. If you have an ethernet RFI problem, look into replacing hubs with switches. Again, that's the case with consumer-grade goods. Commercial grade are much better at this. I beg to differ. Hubs (repeaters) are quite different from switches (multiport bridges) in operation. The problem is that the hubs will transmit into a CAT5 cable with nothing at the other end. Common mode rejection on the pair will prevent it from radiating. However, the high VSWR caused by the lack of a termination, might cause it to radiate. It doesn't make any difference whether you are talking hubs or switches. Some consumer cheap grade hubs may transmit into unterminated lines. But better consumer grade and commercial grade hubs will not. They detect the presence/absence of a device on the other end and operate accordingly. "Understanding and Eliminating RF Interference" by Jim Brown K9YC http://www.audiosystemsgroup.com/RFIHamNCCC.pdf Start reading at Page 20 for the ethernet radiation section. Mo http://www.audiosystemsgroup.com/publish.htm I think our expertise of doing this as a business for years in both residential and commercial establishments qualifies us. With all due respect, that sounds like bluster. You may very well have had hundreds of successful installations, but I question if they were all tested for RFI. I don't really care what you think. And I didn't say they all were tested for RFI - but a good percentage of them were. But it sounds like even if we only tested one for RFI, it would be one more than you have ever done. This thread may also be of interest: http://lists.contesting.com/_rfi/2008-11/msg00025.html Note that 100baseT is quieter than 10baseT. With 100baseT, the data is first 4B5B encoded at 125Mbits/sec. To reduce crosstalk, it is then scrambled and MLT-3 encoded. The result is a 31.2MHz carrier and a mess of sidebands. The necessary scrambling has the side effect of reducing high power peaks, and evening out the power spectrum over a wider frequency range, thus reducing the RFI power at any given frequency. It's much the same idea as the "spread spectrum" modulation of computer clocks, to spread the power over a wider frequency range, to meet FCC Part 15 requirements. So, instead of a carrier or birdie, you'll hear broadband noise, which I guess is more tolerable. Again, it depends on the installation and equipment being used. But 10baseT is also old technology. 100baseT is more recent and solves a lot of problems - both in radiation and susceptibility to interference from external radiation. Agreed. Things do depend on the equipment and installation. Personally, I only do quality installations and use only the best equipment. For example: http://www.LearnByDestroying.com/jeffl/pics/drivel/slides/mess01.html I've seen worse, but the owners didn't want me posting photos. Low voltage systems have been our business for over 10 years. We wouldn't have a successful business if we did crap. And it is our full-time business, not some sideline. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
Turning a 1/4 wave vertical upside down
On 12/16/2013 10:44 PM, Jeff Liebermann wrote:
On Mon, 16 Dec 2013 11:21:30 -0800, David Harmon wrote: On Sun, 15 Dec 2013 23:43:26 -0800 in rec.radio.amateur.antenna, Jeff Liebermann wrote, Marginally related RF drivel: One of my friends is avid DX'er. He has all his media and computer gizmos interconnected via Wi-Fi because Wi-Fi creates less RFI than ethernet. Woah, how can that be? Would using shielded cat6 fix it? I don't know. I don't have much experience with CAT6 STP as most of my installations use CAT5e UTP cable (including for gigabit). It might reduce radiation by shielding, or increase it if there's a ground loop. In any case, the owner was not interested in wiring the house, station, garage, antenna farm, front gate, home theater, etc for ethernet. Wi-Fi did the job well enough and did not product RFI. In retrospect, I probably should have spent more time finding the exact sources of the HF interference. I did not make a systematic check of the house, and did not check everything electrical in the house. I didn't have the time as that would have taken days. Instead, there was a large drop in RFI observed when the ethernet connected devices were unplugged, so we went with that. Actually, if you have the right equipment, you can narrow it down in a very short time. It seldom takes us more than an hour to find RFI problems, and most can be done in 10-15 minutes. It never takes us days, even in large installations. -- ================== Remove the "x" from my email address Jerry Stuckle JDS Computer Training Corp. ================== |
Turning a 1/4 wave vertical upside down
On 12/16/2013 9:58 PM, Jeff Liebermann wrote:
On Mon, 16 Dec 2013 14:27:17 -0600, amdx wrote: On 12/2/2013 12:39 AM, Jeff Liebermann wrote: Comcast is now all digital in the People's Republic of Santa Cruz CA. I got my cable bill a few days ago, noted it had increased $10.00. Told the wife, she said ya, after Nov. the reduction I got last Nov. expired. She went in, made her yearly complaint, but this time she got a $20.00 discount! The bill dropped from $123.54 to $103.xx. (Cable, phone and internet) $240 a year, I think I'll taker her out for an ice cream cone. :-) Mikek Nice, but you can do better than giving her just an ice cream cone. Do I get an ice cream cone if I suggest you drop the cable TV and phone, and leave the internet. Then, switch to a VoIP provider and watch IPTV via Netflix and such? My guess price is: Comcast internet $50/month for first 12 months Comcast internet $80/month after first 12 months Future-Nine America Free $13.50/month Netflix $8/month Roku 3 media player $90 SIP phone (SPA941) $80 Send the ice cream to the address below. I like my Foxnews network, otherwise dropping cable would be easier. I did a short search of IPTV and only found Kansas has googlefiber with a managed IPTV service. I'm not sure what that all means, but the little reasearch I did, I don't think I could have Foxnews on IPTV via Netflix, yet. As I've said before, my kids got Netflix and never concerned themselves with cable. Mikek PS. I'm mulling over the logistics of sending an ice cream cone from Fl. to Ca. :-) |
Turning a 1/4 wave vertical upside down
On 12/17/2013 9:28 AM, amdx wrote:
On 12/16/2013 9:58 PM, Jeff Liebermann wrote: On Mon, 16 Dec 2013 14:27:17 -0600, amdx wrote: On 12/2/2013 12:39 AM, Jeff Liebermann wrote: Comcast is now all digital in the People's Republic of Santa Cruz CA. I got my cable bill a few days ago, noted it had increased $10.00. Told the wife, she said ya, after Nov. the reduction I got last Nov. expired. She went in, made her yearly complaint, but this time she got a $20.00 discount! The bill dropped from $123.54 to $103.xx. (Cable, phone and internet) $240 a year, I think I'll taker her out for an ice cream cone. :-) Mikek Nice, but you can do better than giving her just an ice cream cone. Do I get an ice cream cone if I suggest you drop the cable TV and phone, and leave the internet. Then, switch to a VoIP provider and watch IPTV via Netflix and such? My guess price is: Comcast internet $50/month for first 12 months Comcast internet $80/month after first 12 months Future-Nine America Free $13.50/month Netflix $8/month Roku 3 media player $90 SIP phone (SPA941) $80 Send the ice cream to the address below. I like my Foxnews network, otherwise dropping cable would be easier. I did a short search of IPTV and only found Kansas has googlefiber with a managed IPTV service. I'm not sure what that all means, but the little reasearch I did, I don't think I could have Foxnews on IPTV via Netflix, yet. As I've said before, my kids got Netflix and never concerned themselves with cable. Mikek PS. I'm mulling over the logistics of sending an ice cream cone from Fl. to Ca. :-) Other problems with Netflix include lack of live sports and limited local channels. Some of these are available via the internet (for a price, of course, which must also be factored in). But some, like major league baseball, are blacked out on the internet if you're in their local area; i.e. we can't get either the Baltimore Orioles or Washington Nationals via the internet here in the Washington, DC area. Sure, you could use a proxy somewhere else, but that's against their TOS and if you're caught they will cancel your account with no refund. Additionally, VOIP has had problems in the past, but is getting better. Commercial grade VOIP is pretty solid, but costs more. Consumer grade is more prone to dropped calls and dropouts, but is getting a lot better. Also, the cheaper services are more prone to problems than the more expensive ones. And some phones will not allow more than one extension to be active concurrently (i.e. you can't have two people on the phone on your end talking to someone else). Just some things to check for if they are important to you. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
Turning a 1/4 wave vertical upside down
On Tue, 17 Dec 2013 08:28:16 -0600, amdx wrote:
I like my Foxnews network, otherwise dropping cable would be easier. When you buy a Roku or similar screaming media player, you get a mess of "channels" with it. All they do is point to sources of streaming media all over the internet. FoxNoise is one of those: http://www.roku.com/channels/#!details/2946/fox-news-channel I did a short search of IPTV and only found Kansas has googlefiber with a managed IPTV service. I'm not sure what that all means, but the little reasearch I did, I don't think I could have Foxnews on IPTV via Netflix, yet. IPTV simply means watching television over something that spits internet protocol packets. For example, I watch TV over a rather slothish 1.5Mbit/sec DSL line. Netflix and some others adjust their compression and speed to match the line speed, so they work just fine. Other's just belch at higher rates resulting in the dreaded "buffering" delays. Still others insist on downloading short clips (about 5 min) into the media player buffer, before playing. IPTV is far from a perfect replacement for cable or satellite TV, but it's getting better. A few more details... If you're into playing recorded videos, look into setting up a Plex media server: http://www.plexapp.com Netflix does not do local programming. So, if you want that, setup an outside TV antenna and watch OTA (over the air) TV. To me, the real benefit of watching Netflix over cable or satellite TV is the lack of commercials. As I've said before, my kids got Netflix and never concerned themselves with cable. Good. The kids can set it up for you. Mikek PS. I'm mulling over the logistics of sending an ice cream cone from Fl. to Ca. :-) A gift certificate from the local dispensary will suffice: http://www.lovemariannes.com I'm partial to (dark) chocolate chip. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Turning a 1/4 wave vertical upside down
On Tue, 17 Dec 2013 07:42:01 -0500, Jerry Stuckle
wrote: Actually, if you have the right equipment, you can narrow it down in a very short time. What is the right equipment? A portable spectrum analyzer is not in my budget and my bench test equipment is too heavy for sniffing in the field. I'm fairly well equipped for 2.4GHz wi-fi interference, but not for HF. It seldom takes us more than an hour to find RFI problems, and most can be done in 10-15 minutes. It never takes us days, even in large installations. Impressive. I assume those are continuously generating RFI sources, not sources that appear intermittently or drift all over the place as they warm up. I spent about a month chasing down a noise source that turned out to be the 24v battery charger on a diesel generator. Some grid tied solar controllers seem to be problems and take some time to find because they can be miles away. Fortunately, they're usually easily fixed with the manufacturers optional filter kit. It took me about a week to determine that my weather station was the source of some 20 meter trash. The problem was that it only generated noise when running on the internal backup battery, and not on AC power. The ones that disappear when the AC power is temporarily turned off are usually quite easy. The one's that don't take me much longer to find. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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