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Relationship Between Antenna Efficiency and Received Signal Strength
"Jerry Stuckle" wrote in message ... On 1/22/2014 5:32 PM, Irv Finkleman wrote: Q. Is there a relationship between the efficiency of an antenna and the received signal strength? Definitely. Antenna efficiency works both ways - a less efficient antenna will affect both transmit and received signals. Just pondering on the matter. Because I have to operate with restricted space antennas, usually with low efficiency, I wonder how much of a relationship exists between Efficiency and Received Signal Strength? Just as much as between efficiency and transmitted signal strength. This leads to more questions such as how much do radials contribute to efficiency? That depends on a lot of factors such as number of radials, length, height above ground and ground conductivity, for start. Each situation is different. But generally, for antennas such as 1/4 wave verticals, radials will help. IF that isn't enough, how much do radials contribute to the bandwidth? See above. And... And... I'm never to old to learn, but I am old enough that a lot of mathematical mumbo jumbo and Smith Charts tend to confound me! Unfortunately, the only way to predict how an antenna is going to work in a specific situation with any accuracy is with math and Smith Charts. So you can use the "tried and true" method - put it up and see what happens :) In this case the smith chart and antenna modling programs probably won't work. In the small confins there are too many variables in the near field of the antenna. Not that the program would not work, but it might take years to measuer everything in the near field of the antenna. Like you said , the tried and true method. Put something up and see how it works. Often people tend to overthink a simple problem or over think a problem there is no easy solution for. For now, it might be just as good and easy to tack a dipole up in the cealing of the room even if it is bent at all kinds of angles. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com |
Relationship Between Antenna Efficiency and Received Signal Strength
On Friday, January 24, 2014 7:21:42 AM UTC-6, Jerry Stuckle wrote:
Low antenna efficiency affects not only the received signal, but the received noise. Of course. I've already said that several times. But they effect both equally, so the s/n ratio will stay the same assuming the overall level is overriding the recv internal noise. And yes, many inexpensive "modern" receivers suffer from poor front ends. Most will be good enough not to see the problems you are mentioning though. Like I say, you'll have to see almost nothing at all from the antenna system to have that problem. Even my dinky mobile antennas greatly swamp the internal noise, even on 10m, when using my Icom 706mk2g. Heck, I've never had or used an antenna system that was bad enough to see the problem you are mentioning. |
Relationship Between Antenna Efficiency and Received Signal Strength
On Fri, 24 Jan 2014 13:04:48 -0500, Jerry Stuckle
wrote: The easiest way of seeing it is looking at the output of both tube and transistorized transmitters on a spectrum analyzer. You will see much more hash on the transistorized transmitter. Amazing. You might see more hash with a synthesized transistor xmitter, but for crystal controlled, they noise is quite a bit less with transistors. Back in the 70's, I ran a CAP repeater from my home. Transmit and receive antennas were separated by about 25' vertically. It was a surplus Motorola tube rig, running 25W. I was able to run it without any desense without duplexers. Yes, the channel spacing was 4.25Mhz, but you can't do that with a transistorized rig. Amazing. These days, 2 meter repeaters do 0.600 MHz spacing using all transistor equipment, a single antenna, and a notch type duplexer. Yes, nowadays, there are transistors with lower noise figures. But they are relatively expensive, and you won't find them in the less expensive receivers. Rubbish. pHEMT devices are available with 0.75dB NF at 1GHz for under $3/ea. For example: http://www.minicircuits.com/pdfs/PSA4-5043+.pdf Note that this isn't just a single device but a MMIC amplifier capable of belching 100 mw (+20dBm) with 1dB gain compression. I seem to remember that most tube sets of the old days were stating about .5 uv senstivity on ssb, and many of todays ham trasceivers are way less than that. That depends on the frequency. The atmospheric noise is so high on the lower HF bands that improvments in receiver sensitivity simply results in amplifying both the noise and the signal but the same amount, resulting in no net improvement in signal to noise ratio (SNR). Adding more gain also decreases the receiver dynamic range because at high signal levels, the added gain will cause the receiver to overload at a lower signal level. Hint: Use only as much gain as necessary and no more. Plus or minus, that is about right. But that wasn't because of the tubes; they could have done better but it would have required more amplification and higher cost. Plus with a decent antenna, the atmospheric noise was higher than that, so there was no need for more amplification. It would have just been lost in the AGC circuitry. Mostly I agree except for the part about AGC. If your receiver is already into AGC for weak signal conditions, you're effectively reducing the receiver sensitivity at the same time. The way AGC is suppose to work for a SSB receiver is that the AGC starts just above the level where you can hear an intelligible signal. 12dB SINAD is about right. If the AGC were perfect (i.e. no slope), then any increase in signal level above that point will result in no improvement in SNR because the AGC will do its best to keep the SNR constant. With a real AGC (dual slope, controlled attack and release time) the SNR improves somewhat as the input level increases until it reaches some SNR, where it levels off. I think this is called "ultimate SNR" or something similar, which is just the SNR of a very strong receive signal. Even back in the early 70's, commercial tube VHF radios could easily get .15mv for 20db S+N/N ratio. Not much different than the transistorized versions today. I think you might mean 0.15 uv/12dB SINAD. A 0.15mv receiver would be considere comatose. In the 1960's thru about 1983, I was involved in various radio service, radio manufacture, radio sales, and radio consulting companies. I had plenty of experience with everything from wideband GE Pre-Prog thru cellular radios including tubes. I never saw a tube receiver with 0.15uv sensitivity. Photos of the shop and various repeaters. Most were UHF. http://802.11junk.com/jeffl/pics/Old...ers/index.html The main site was on Santiago Pk: http://www.trabucooutdoors.com/assets/images-1/odds_ends/santiagopk.jpg The mess on the far right is the antenna farm. 9 GE Progress Line repeaters with Alpha tone panels (which I helped design). http://802.11junk.com/jeffl/pics/Old%20Repeaters/slides/Santiago-01.html See anything missing? There are no duplexers. There was one receive antenna and 9 transmit antennas. All tubes. With a typically 1uv/12dB SINAD receiver, the isolation was sufficient. Don't ask about the tx intermod, which was horrible. Typically, these tube type repeaters would start out with about 0.5uv/12dB SINAD with new tubes. That's measured directly into the receiver input with no additional filters. After about 6 months, the sensitivity would settle down to about 0.75 to 0.90uv and stay there for about 6 to a year, when it needed retuning. This was using a 6AM4 triode. The only time I saw better sensitivity with tubes was when someone tweaked the audio freq response, or excessively narrowed the IF bandwidth. Somewhat later, in the 1970's, I found myself designing marine radios. Typical VHF sensitivity was about 0.25uv/12dB SINAD using a dual gate MOSFET front end such as a 40673 or 3N212. We ocassionally used JFET's such as a U310 but the sensitivity was about the same. The problem is that 0.15uv is just too close to the receiver noise floor to be realizeable. With a 25KHz receive bandwidth: noise floor = -174dBm/Hz + 10*log(25KHz) = -174 + 10*4.40 = -174 + 44 = -130 dBm or 0.071 uv To obtain a 0.15 uv sensitivity, you would need a receiver noise figure plus a detection SNR of less than: 10 log(0.15/0.071) = 3.3dB With an analog FM demodulator, that's barely possible and usually requires a perfect noise-free front end. However, with a 0.25uv/12dB SINAD sensitivity, there's 5.5dB of margin, which is more than enough for real receivers. Mo http://www.r-390a.net/Receiver-Specifications-Explaned.pdf -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Relationship Between Antenna Efficiency and Received Signal Strength
"Jeff Liebermann" wrote in message ... On Fri, 24 Jan 2014 13:04:48 -0500, Jerry Stuckle wrote: The easiest way of seeing it is looking at the output of both tube and transistorized transmitters on a spectrum analyzer. You will see much more hash on the transistorized transmitter. Amazing. You might see more hash with a synthesized transistor xmitter, but for crystal controlled, they noise is quite a bit less with transistors. Back in the 70's, I ran a CAP repeater from my home. Transmit and receive antennas were separated by about 25' vertically. It was a surplus Motorola tube rig, running 25W. I was able to run it without any desense without duplexers. Yes, the channel spacing was 4.25Mhz, but you can't do that with a transistorized rig. Amazing. These days, 2 meter repeaters do 0.600 MHz spacing using all transistor equipment, a single antenna, and a notch type duplexer. What you are saying is more in my line of thinking and limiated expierance. Around 30 years ago I had an Ameco 2 meter receive converter that used the 6ds4 nuvistors. Probably the best tube that most could afford. Tuned for the best signal, I could still improve it when adding a u310 preamp. Not sure how much as I did not have very good test equipment, but noticiable by ear. I think many of the old sets used a 6ak5 for the rf amp. Transmitting noise I don't know. All I was looking at was the noise figure for the receiver as that was the origional topic. What Jerry was talking about was a tube CAP repeater with seperate antennas. If the receiver was around .5 uv or worse and the transmitter was cleaner he could operate with seperate antennas . He said he could do that with the tubes but not the transistors which I believe. Beter selectivity on the transmitter and receiver than some transistor repeaters. I do have a 2 meter repeater on the air with 600 khz seperation. Solid state and 100 watts. Right now it has a Dow East Microwave phet preamp on it. Don't recall the exect sensitivy for 12 db sinad but it is under .2 uv as shown on my hp8924c. No desense is detected. It does have a 6 cavity bpbr duplexer with the high selectivity option. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com |
Relationship Between Antenna Efficiency and Received Signal Strength
On Fri, 24 Jan 2014 20:00:52 -0500, "Ralph Mowery"
wrote: Around 30 years ago I had an Ameco 2 meter receive converter that used the 6ds4 nuvistors. Probably the best tube that most could afford. I built a few preamps using a 6CW4, 6DS4 or an 8056. The Nuvistors were about the best commerical low noise receive tubes available at the time. The 8056 was rated at 4.5dB NF at 200 MHz and 16.4dB of gain. http://www.ko4bb.com/Manuals/RCA/RCA_8056_Nuvistor_AN-195.pdf See the two graphs. A 4.5dB NF was about typical for a good receive tube. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Relationship Between Antenna Efficiency and Received Signal Strength
On 1/24/2014 7:14 PM, Jeff Liebermann wrote:
On Fri, 24 Jan 2014 13:04:48 -0500, Jerry Stuckle wrote: The easiest way of seeing it is looking at the output of both tube and transistorized transmitters on a spectrum analyzer. You will see much more hash on the transistorized transmitter. Amazing. You might see more hash with a synthesized transistor xmitter, but for crystal controlled, they noise is quite a bit less with transistors. You obviously don't use a decent spectrum analyzer. Back in the 70's, I ran a CAP repeater from my home. Transmit and receive antennas were separated by about 25' vertically. It was a surplus Motorola tube rig, running 25W. I was able to run it without any desense without duplexers. Yes, the channel spacing was 4.25Mhz, but you can't do that with a transistorized rig. Amazing. These days, 2 meter repeaters do 0.600 MHz spacing using all transistor equipment, a single antenna, and a notch type duplexer. Sure - WITH DUPLEXERS. I did it WITHOUT DUPLEXERS. A HUGE difference. But obviously one YOU DON'T UNDERSTAND. Do you even know what a duplexer is? (I really doubt it). Yes, nowadays, there are transistors with lower noise figures. But they are relatively expensive, and you won't find them in the less expensive receivers. Rubbish. pHEMT devices are available with 0.75dB NF at 1GHz for under $3/ea. For example: http://www.minicircuits.com/pdfs/PSA4-5043+.pdf Note that this isn't just a single device but a MMIC amplifier capable of belching 100 mw (+20dBm) with 1dB gain compression. Which you don't use in the front end of a receiver. But I see you don't understand anything that's been said in this thread, so no surprise there. I seem to remember that most tube sets of the old days were stating about .5 uv senstivity on ssb, and many of todays ham trasceivers are way less than that. That depends on the frequency. The atmospheric noise is so high on the lower HF bands that improvments in receiver sensitivity simply results in amplifying both the noise and the signal but the same amount, resulting in no net improvement in signal to noise ratio (SNR). Adding more gain also decreases the receiver dynamic range because at high signal levels, the added gain will cause the receiver to overload at a lower signal level. Hint: Use only as much gain as necessary and no more. More true with transistorized rigs than the tube ones. You *could* overload the tube rigs, but it was much harder. Plus or minus, that is about right. But that wasn't because of the tubes; they could have done better but it would have required more amplification and higher cost. Plus with a decent antenna, the atmospheric noise was higher than that, so there was no need for more amplification. It would have just been lost in the AGC circuitry. Mostly I agree except for the part about AGC. If your receiver is already into AGC for weak signal conditions, you're effectively reducing the receiver sensitivity at the same time. The way AGC is suppose to work for a SSB receiver is that the AGC starts just above the level where you can hear an intelligible signal. 12dB SINAD is about right. If the AGC were perfect (i.e. no slope), then any increase in signal level above that point will result in no improvement in SNR because the AGC will do its best to keep the SNR constant. With a real AGC (dual slope, controlled attack and release time) the SNR improves somewhat as the input level increases until it reaches some SNR, where it levels off. I think this is called "ultimate SNR" or something similar, which is just the SNR of a very strong receive signal. No, AGC will not "try to keep the S/N ratio constant". It tries to keep the output of the IF constant. As the signal increases, the noise will decrease, improving the S/N ratio. But you also don't seem to understand how AGC works. Even back in the early 70's, commercial tube VHF radios could easily get .15mv for 20db S+N/N ratio. Not much different than the transistorized versions today. I think you might mean 0.15 uv/12dB SINAD. A 0.15mv receiver would be considere comatose. No, I mean 20db S+N/N ratio. The equivalent SINAD would be somewhere around .12mv (or a bit less). Not at all "comatose". In the 1960's thru about 1983, I was involved in various radio service, radio manufacture, radio sales, and radio consulting companies. I had plenty of experience with everything from wideband GE Pre-Prog thru cellular radios including tubes. I never saw a tube receiver with 0.15uv sensitivity. Photos of the shop and various repeaters. Most were UHF. http://802.11junk.com/jeffl/pics/Old...ers/index.html The main site was on Santiago Pk: http://www.trabucooutdoors.com/assets/images-1/odds_ends/santiagopk.jpg The mess on the far right is the antenna farm. That must be because you were working on GE Pre-Prog. I worked with both Motorola and RCA sets (plus a few others which weren't quite as good). We were able to get them to .15mv. on VHF. But then according to you, such a radio would be "comatose". I wonder just how bad your GE's were? 9 GE Progress Line repeaters with Alpha tone panels (which I helped design). http://802.11junk.com/jeffl/pics/Old%20Repeaters/slides/Santiago-01.html See anything missing? There are no duplexers. There was one receive antenna and 9 transmit antennas. All tubes. With a typically 1uv/12dB SINAD receiver, the isolation was sufficient. Don't ask about the tx intermod, which was horrible. 1mv/12DB SINAD is terrible. Such a receiver would never have left our shop. Typically, these tube type repeaters would start out with about 0.5uv/12dB SINAD with new tubes. That's measured directly into the receiver input with no additional filters. After about 6 months, the sensitivity would settle down to about 0.75 to 0.90uv and stay there for about 6 to a year, when it needed retuning. This was using a 6AM4 triode. The only time I saw better sensitivity with tubes was when someone tweaked the audio freq response, or excessively narrowed the IF bandwidth. 0.5mv wouldn't leave our shop, either. And both Motorola and RCA rigs would hold their sensitivity for much longer than that, even in a mobile installment. Somewhat later, in the 1970's, I found myself designing marine radios. Typical VHF sensitivity was about 0.25uv/12dB SINAD using a dual gate MOSFET front end such as a 40673 or 3N212. We ocassionally used JFET's such as a U310 but the sensitivity was about the same. Yea, one of the shops I worked at sold similar quality rigs, mainly for those who wouldn't pay for a good RCA. The Motorola shop didn't sell anything else, of course. The problem is that 0.15uv is just too close to the receiver noise floor to be realizeable. With a 25KHz receive bandwidth: noise floor = -174dBm/Hz + 10*log(25KHz) = -174 + 10*4.40 = -174 + 44 = -130 dBm or 0.071 uv To obtain a 0.15 uv sensitivity, you would need a receiver noise figure plus a detection SNR of less than: 10 log(0.15/0.071) = 3.3dB With an analog FM demodulator, that's barely possible and usually requires a perfect noise-free front end. However, with a 0.25uv/12dB SINAD sensitivity, there's 5.5dB of margin, which is more than enough for real receivers. Mo http://www.r-390a.net/Receiver-Specifications-Explaned.pdf Maybe in your designs, but not in the ones most of our clients demanded and paid for. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
Relationship Between Antenna Efficiency and Received Signal Strength
On 1/24/2014 8:00 PM, Ralph Mowery wrote:
"Jeff Liebermann" wrote in message ... On Fri, 24 Jan 2014 13:04:48 -0500, Jerry Stuckle wrote: The easiest way of seeing it is looking at the output of both tube and transistorized transmitters on a spectrum analyzer. You will see much more hash on the transistorized transmitter. Amazing. You might see more hash with a synthesized transistor xmitter, but for crystal controlled, they noise is quite a bit less with transistors. Back in the 70's, I ran a CAP repeater from my home. Transmit and receive antennas were separated by about 25' vertically. It was a surplus Motorola tube rig, running 25W. I was able to run it without any desense without duplexers. Yes, the channel spacing was 4.25Mhz, but you can't do that with a transistorized rig. Amazing. These days, 2 meter repeaters do 0.600 MHz spacing using all transistor equipment, a single antenna, and a notch type duplexer. What you are saying is more in my line of thinking and limiated expierance. Around 30 years ago I had an Ameco 2 meter receive converter that used the 6ds4 nuvistors. Probably the best tube that most could afford. Tuned for the best signal, I could still improve it when adding a u310 preamp. Not sure how much as I did not have very good test equipment, but noticiable by ear. I think many of the old sets used a 6ak5 for the rf amp. Transmitting noise I don't know. All I was looking at was the noise figure for the receiver as that was the origional topic. What Jerry was talking about was a tube CAP repeater with seperate antennas. If the receiver was around .5 uv or worse and the transmitter was cleaner he could operate with seperate antennas . He said he could do that with the tubes but not the transistors which I believe. Beter selectivity on the transmitter and receiver than some transistor repeaters. I do have a 2 meter repeater on the air with 600 khz seperation. Solid state and 100 watts. Right now it has a Dow East Microwave phet preamp on it. Don't recall the exect sensitivy for 12 db sinad but it is under .2 uv as shown on my hp8924c. No desense is detected. It does have a 6 cavity bpbr duplexer with the high selectivity option. Receiver sensitivity was 0.2 mv for 20db S+N/N ratio. I don't know how much better; the surplus signal generator I was using wasn't that accurate. And BTW - 'm' can also mean micro, especially when you don't have a Greek alphabet available. 'u' is not the same as the Greek 'mu' and can be confusing. Of course, using 'm' for both milli and micro can be confusing, unless you know the context. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
Relationship Between Antenna Efficiency and Received Signal Strength
"Irv Finkleman" wrote in message ... Thanks for all the replys guys. Just to set the record straight, I have been a ham for over fifty years, and a very active member of the local ham club for over 30 (since I moved to Calgary). I hold an advanced ticket and am not totally ignorant on matters re antennas. I am a darned good tech (most of my gear was bought broken and I fixed it up), but sometimes I need simple answers to a few questions -- and this is the place for that! Irv-- I have had "reasonable" results using a horizontal loop strung around the top of the shack walls. I used buttons for insulators, and thread to fasten the buttons to the wall via thumbtacks. The wire was 28 ga if I recall. My first attempt was with a 15 meter loop. I had a little extra space, so I just made the loop a little larger and used a tuner to calm things down. This is not the ultimate antenna, but isn't too bad considering that it is indoors. Good luck with your living arrangement and ham activities. Wayne W5GIE Redlands, CA |
Relationship Between Antenna Efficiency and Received Signal Strength
Thanks Wayne,
Its not a bad idea and I've considered horizontal loops but if you knew what was in my ceiling I think you'd reconsider too! In any event, I'm all studied up and planned on building a magnetic loop which will meet all my needs. Thanks for your consideration, Irv VE6BP |
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