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Relationship Between Antenna Efficiency and Received Signal Strength
Q. Is there a relationship between the efficiency of an antenna and the
received signal strength? 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? This leads to more questions such as how much do radials contribute to efficiency? IF that isn't enough, how much do radials contribute to the bandwidth? 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! For starters, I will be operating using an MP-1 antenna and a Yaesu FT-817ND. I also have an MFJ-931 Artificial Ground, but propose attaching the radials to the feedpoint on the MP-1. I intend to cut four radials for 20M and spread them around the base of the antenna in my room, and once the weather warms up, I'll try the antenna out on the balcony with the radials spread around whatever real estate it provides. Thanks for any input on the matter.... Irv VE6BP RADIATE OR DIE TRYING! |
Relationship Between Antenna Efficiency and Received Signal Strength
On Wed, 22 Jan 2014 15:32:31 -0700, "Irv Finkleman"
wrote: Q. Is there a relationship between the efficiency of an antenna and the received signal strength? Not really. Radiation efficiency is normally used with transmitting antennas, not receiving. You're not radiating anything in receive. http://en.wikipedia.org/wiki/Antenna_efficiency 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? Any loss of receive efficiency will show up in the antenna gain (or lack of antenna gain). No need to deal with it separately. This may help with conversions and computations: http://www.tscm.com/fieldint.pdf This leads to more questions such as how much do radials contribute to efficiency? I assume you mean ground radials, not antenna radials. The purpose of the ground radials is to prevent the RF that's being radiated towards the ground, from getting absorbed by the ground. With above ground radials, they reflect the signal upwards, so that part of the signal goes in hopefully some useful direction. (Note: This is not the conventional wisdom). IF that isn't enough, how much do radials contribute to the bandwidth? That's what antenna models and simulations are for. Much depends on the conductivity of the ground, the size and number of radials, type of antenna, etc. 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! See: http://www.qsl.net/4nec2/ or http://www.eznec.com Both come with a large collection of ready to play antennas. Take your location, your antenna, your ground, and your imagination, and make a model. I've done that for my house. It started out fairly simple, and has grown into a monster that takes hours to compute. Still, it's quite worthwhile to see what changes, such as your ground system, does to the pattern, gain, bandwidth, vswr, etc. Incidentally, you can have: Gain, bandwidth, or size. Pick any two. What that means is that if you shrink the antenna, you're going to lose either gain or bandwidth. No free lunch in antenna land. For starters, I will be operating using an MP-1 antenna and a Yaesu FT-817ND. I also have an MFJ-931 Artificial Ground, but propose attaching the radials to the feedpoint on the MP-1. I intend to cut four radials for 20M and spread them around the base of the antenna in my room, and once the weather warms up, I'll try the antenna out on the balcony with the radials spread around whatever real estate it provides. Sorry, no clue to what it will do. I convinced a friend to run his 2nd floor station with some welded fence wire under his carpet. It worked fine until his wife made him remove the wire. Nothing would roll over the carpet. Thanks for any input on the matter.... Never thank anyone until it's done and working. Premature thanks is bad luck. Irv VE6BP RADIATE OR DIE TRYING! Calculations are worth more than the usual cut-n-try. -- 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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The very best advice we can give you is to advise you to find a good amateur radio club in your neighborhood and have you join. Look for someone more knowledgeable then yourself - regardless of their age, and have them mentor you. A decent Amateur Radio Club will have a hamshack - a place where it's members can operate. There - you can take your radio and hook it up to their antenna's and operate. The only other advice I can give you is to tell you to move! Amateur radio isn't for everyone. It does not allow us to bend or break the rules of Physic's. There is a certain amount of effort that has to be done in order to get your signal up in the air and be able to broadcast it to the world. The only option I have seen that was somewhat successful was a operator that bought Hamsticks and fabricated a mount, mounted the hamsticks on his porch railing, grounded the railing and used the hamsticks on 6 and 10 meters. 10 meters only requires a 9' long antenna - quarter wave, and a dipole on 6 is 9' long. Your transceiver is marginal at best, not a real good performer to start with and handicapping it by using a non resonant antenna is only going to impede your amateur radio hobby much past listening to the bands. |
Relationship Between Antenna Efficiency and Received Signal Strength
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 :) For starters, I will be operating using an MP-1 antenna and a Yaesu FT-817ND. I also have an MFJ-931 Artificial Ground, but propose attaching the radials to the feedpoint on the MP-1. I intend to cut four radials for 20M and spread them around the base of the antenna in my room, and once the weather warms up, I'll try the antenna out on the balcony with the radials spread around whatever real estate it provides. Not an ideal situation, but you do what you can. Thanks for any input on the matter.... Irv VE6BP RADIATE OR DIE TRYING! -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
Relationship Between Antenna Efficiency and Received Signal Strength
"Irv Finkleman" wrote in message ... Q. Is there a relationship between the efficiency of an antenna and the received signal strength? 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? Most of your problem is not going to be with the receiver. I am thinking that Yaesu is around 5 watts or less. For the most part you can just throw out any kind of antenna and hear lots more than you will be able to work with 5 watts. You can probably stick 10 to 15 feet of wire in the back of the rig and hear as much as you can with the MP-1 antenna in the same room. First I would get rid of that rig and get one with 100 watts out. Not that you can't work stations with 5 watts, but you will make many more cotacts with around 100 watts on a miminal antenna. For the antenna put up anything you can. You may need a good tuner to match the antenna. You did not say if you are in an apartment on a high floor. If so, stick up what ever you can vertical and load it with a coil if needed, and drop a wire toward the ground for about 1/4 wavelength. Forget about really trying to chart and graph any antenna for your situation, Just throw up something and get on the air. I would almost recommend one of the screwdriver type antennas and some wire for a ground plane or lower part of a dipole for your situation. For 20 meters and up you may give a dipole made out of 2 of the Hamstick type antennas a try. --- 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
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! BUT! -- for the past four years I have been in and out of the hospital and off and on some pretty mind bending medications -- consequently sometimes I cannot think as straight as when I was younger, nor do I move around well. I'm not yet demented but do admit to being crazy but not dangerous! I am somewhat handicapped, and live in a senior's residence. I cannot have an outside antenna other than what I can fit on a small (6'x9' balcony. I can have a whip sticking over the side, but I still need to remain relatively invisible (all I tell the other residents is that it is for listening to shortwave lest I be blamed for non-functioning TV remote controls, cordless phones with low batteries, and the like). I plan to build a magnetic loop this summer, but winter hangs around here until about the end of May! In the meantime I am trying to figure what I can do to operate from within the confines of my studio suite -- once the loop is built I can put it on the balcony and tune it remotely from inside. I intend to operate QRP using an FT-817ND. Once I find I can operate undetected, I also have an FT-857 and may go to a few more watts. Insofar as radials are concerned, they will be laid around the base of the antenna, mainly for the purpose of getting the best match possible for the MP-1 vertical antenna, or any other things I may try in the future. I've had a number of suggestions to use hamsticks in a dipole configuration (won't fit on the balcony and makes band changing difficult), baluns (not required with the whip or a magnetic loop), higher power to overcome antenna inefficiency, and how easy it is to learn to use a Smith Chart, and even move. I'm where I plan to stay (I get great medical care here, and the nurses are cute -- when I leave, they'll have to carry me out. So, as I've said before, it's a case of 'RADIATE OR DIE TRYING!'. Suggestions that I go to higher power, buy a screwdriver antenna, and hints about baluns, don't help -- I've got to make do with what I have on hand, and I will do it. My main question asking whether there is a relationship between antenna efficiency and received signal strength (will a more efficient antenna result in a higher S-meter indication?) is all I really wanted to ask. The radial matter was simply a possible way to increase the efficiency (by reducing ground losses). Power-wise is not a problem for me -- it's not a matter of contact quantity but quality. It's sort of like fly-fishing versus the dynamite fishing lure. If I get one good QSO a day, I'll be happy. I have trouble moving around physically so that's why I'm so slow in collecting the materials I need, and getting something going, but I want to do it slowly, but surely. I have a couple of ham chums who will help me as needed. I just got enough wire to make some radials for 20M, so I'll cut and throw them around the base of the MP-1 and see what I can do. Eventually I'd like to work 80 thru 10M but that's for later. Thanks for your replies and suggestions, many of which have been helpful, but bear with me -- I'm getting there slowly, and with a little luck the end is in sight! It's just that I can't do anything very quickly, but with time I'll do it all! 73 Irv VE6BP |
Relationship Between Antenna Efficiency and Received Signal Strength
On 1/22/2014 4:32 PM, Irv Finkleman wrote:
Q. Is there a relationship between the efficiency of an antenna and the received signal strength? 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? This leads to more questions such as how much do radials contribute to efficiency? IF that isn't enough, how much do radials contribute to the bandwidth? 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! For starters, I will be operating using an MP-1 antenna and a Yaesu FT-817ND. I also have an MFJ-931 Artificial Ground, but propose attaching the radials to the feedpoint on the MP-1. I intend to cut four radials for 20M and spread them around the base of the antenna in my room, and once the weather warms up, I'll try the antenna out on the balcony with the radials spread around whatever real estate it provides. Thanks for any input on the matter.... Irv VE6BP RADIATE OR DIE TRYING! Irv, I have a pdf file about ham antennas that is written in very nice plain language and explains all the benefits and downfalls of different types of antennas and grounds. If your email is correct I will send it to you. Michael |
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Smith Charts do not have anything to do with antenna efficiency or resonance. The only thing that Smith Charts does is explain what is happening inside of a piece of coax X inches long. Note I do not use feet - since that is too vague. |
Relationship Between Antenna Efficiency and Received Signal Strength
On Wednesday, January 22, 2014 4:32:31 PM UTC-6, Irv Finkleman wrote:
Q. Is there a relationship between the efficiency of an antenna and the received signal strength? Signal to noise ratio, very little. Received signal level vs a more efficient antenna, can be quite a bit. But if the s/n is appx the same, no biggie.. Lower level on the S meter, but things should sound about the same when listening to it. 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? It all depends what freq, type of operation, etc.. But for general skywave HF, even a fairly inefficient antenna can be quite fine for receiving in many cases. The level may drop with the inefficient antenna, but assuming the same basic pattern, the s/n ratio should be pretty much the same. If you have enough antenna to increase the background noise when connecting the antenna to the radio, it should be fine for general gov use. This leads to more questions such as how much do radials contribute to efficiency? Quite a bit, but that's much more a transmitting concern than receive. IF that isn't enough, how much do radials contribute to the bandwidth? In general, adding more radials will decrease the bandwidth. For starters, I will be operating using an MP-1 antenna and a Yaesu FT-817ND. I also have an MFJ-931 Artificial Ground, but propose attaching the radials to the feedpoint on the MP-1. I intend to cut four radials for 20M and spread them around the base of the antenna in my room, and once the weather warms up, I'll try the antenna out on the balcony with the radials spread around whatever real estate it provides. You would be much better off ditching the vertical idea, and try to figure out a way to string up a simple dipole for one of the higher bands. If you have room for radials, you should have enough room for a simple dipole. And it doesn't have to be inline, or in any particular orientation. For 20m, you could have a feed point in one of the corners of a room, and have one 16 ft leg running along one wall, and have the other leg running down the other wall. The legs would be 90 degrees apart, but will still work fine overall. The antenna will be efficient if fed with thin coax, and likely beat the pants off most small vertical rigs. But this sort of assumes there is not wiring or metal in the walls to grossly detune the antenna. In your case, receiving should be no problem. Even a length of random wire will work for general HF. Your real issue is radiating enough RF for people to hear you. One thing about "short" verticals. A good ground/radial system is more critical for those than it is for full length monopoles which can often get by with no/few radials and still work well enough to use. That's much harder to do with a very short loaded vertical. If I were you, I'd be trying to find ways to run sneaky dipoles. You could use real thin wire if needed to make it less visible. If you stick to the higher bands, they won't be too long. You can do 10m nicely if you can find a way to string up 16 ft of wire total. Even a 32 ft 20 m dipole can be fit into many rooms. Feed with thin coax, and no tuner, no tuner loss, and the efficiency will be high. That's what you want with QRP. |
Relationship Between Antenna Efficiency and Received Signal Strength
Thanks Mark -- you answered my questions. I sort of knew the
answers but needed confirmation in my own mind. If you read my post in the topic 'antenna theory made easy' you will understand why dipoles are out of the question. Real Estate is my limiting factor! A magloop will be built and should be running early this summer -- earlier if weather permits! Irv VE6BP |
Relationship Between Antenna Efficiency and Received Signal Strength
wrote in message ... It all depends what freq, type of operation, etc.. But for general skywave HF, even a fairly inefficient antenna can be quite fine for receiving in many cases. The level may drop with the inefficient antenna, but assuming the same basic pattern, the s/n ratio should be pretty much the same. If you have enough antenna to increase the background noise when connecting the antenna to the radio, it should be fine for general gov use. I always hear that, but it doesn't seem to be that way for me. I have an off center fed antenna (about 125 feet long) mostly flat at 50 feet. Also a 3 element triband at 60 feet. Both fed by low loss rg8 type coax. On some of the weaker signals on 20 meters I don't hear signals on the OCF that are good copy on the beam. Also an 80 meter dipole at the 45 foot level at right angles to the 80 meter antenna will not hear what the beam does in some cases. That is in a relative quiet location as far as noise goes. The receive is an Icom 746pro. --- 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 1/23/2014 3:30 PM, Channel Jumper wrote:
Jerry Stuckle;814478 Wrote: 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? - 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. 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 :) ================== I'm sorry Jerry, but you don't know what you are talking about. Smith Charts do not have anything to do with antenna efficiency or resonance. The only thing that Smith Charts does is explain what is happening inside of a piece of coax X inches long. Note I do not use feet - since that is too vague. Again, wrong. Smith Charts explain a LOT about antennas. But then I can see you've never used one - but you have to try to correct someone who knows more than you, anyway. But you only show your ignorance. And BTW - I was using Smith Charts before you were born. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
Relationship Between Antenna Efficiency and Received Signal Strength
On Thursday, January 23, 2014 7:16:54 PM UTC-6, Ralph Mowery wrote:
wrote in message ... It all depends what freq, type of operation, etc.. But for general skywave HF, even a fairly inefficient antenna can be quite fine for receiving in many cases. The level may drop with the inefficient antenna, but assuming the same basic pattern, the s/n ratio should be pretty much the same. If you have enough antenna to increase the background noise when connecting the antenna to the radio, it should be fine for general gov use. I always hear that, but it doesn't seem to be that way for me. I have an off center fed antenna (about 125 feet long) mostly flat at 50 feet. Also a 3 element triband at 60 feet. Both fed by low loss rg8 type coax. On some of the weaker signals on 20 meters I don't hear signals on the OCF that are good copy on the beam. Also an 80 meter dipole at the 45 foot level at right angles to the 80 meter antenna will not hear what the beam does in some cases. That is in a relative quiet location as far as noise goes. The receive is an Icom 746pro. That would almost surely be more pattern related than efficiency. And the beam has gain in the direction it's pointing. If you took any one of those antennas on it's own and lowered the efficiency by adding resistance at the feed, a more lossy feed line, or added tuner loss, or even just used an attenuator, the signal level will vary, but the s/n ratio should change very little. Both the noise and desired signals are going to be reduced equally. Only when you get to the point where hooking up the antenna and not noticing a noise increase at all, are you starting to really have a problem with reception due to lower system efficiency. |
Relationship Between Antenna Efficiency and Received Signal Strength
On Thursday, January 23, 2014 8:21:27 PM UTC-6, Jerry Stuckle wrote:
On 1/23/2014 7:18 PM, wrote: On Wednesday, January 22, 2014 4:32:31 PM UTC-6, Irv Finkleman wrote: Q. Is there a relationship between the efficiency of an antenna and the received signal strength? Signal to noise ratio, very little. Received signal level vs a more efficient antenna, can be quite a bit. But if the s/n is appx the same, no biggie.. Lower level on the S meter, but things should sound about the same when listening to it. You forgot the noise generated by the receiver. With a weaker signal, the S/N ration will be lower. That would be an issue on VHF/UHF. We are talking HF here. On HF, external noise picked up by the antenna is almost surely going to greatly swamp any internal receiver noise. Assuming a decent receiver anyway, and the one he has should be fairly good. That's one reason why I say if the background noise increases when connecting the antenna, it should be good enough. If it doesn't, there could be a problem. But it will take a really dead antenna system to be like that on HF. Even just sticking a 5 feet piece of wire into the center pin of a decent receiver will cause the noise level to increase, and thus be a fairly viable antenna. Not that it's going to pick up everything, but it should pick up quite a bit. Note the portable SW radios with short whips, etc.. |
Relationship Between Antenna Efficiency and Received Signal Strength
On 1/23/2014 9:42 PM, wrote:
On Thursday, January 23, 2014 8:21:27 PM UTC-6, Jerry Stuckle wrote: On 1/23/2014 7:18 PM, wrote: On Wednesday, January 22, 2014 4:32:31 PM UTC-6, Irv Finkleman wrote: Q. Is there a relationship between the efficiency of an antenna and the received signal strength? Signal to noise ratio, very little. Received signal level vs a more efficient antenna, can be quite a bit. But if the s/n is appx the same, no biggie.. Lower level on the S meter, but things should sound about the same when listening to it. You forgot the noise generated by the receiver. With a weaker signal, the S/N ration will be lower. That would be an issue on VHF/UHF. We are talking HF here. On HF, external noise picked up by the antenna is almost surely going to greatly swamp any internal receiver noise. Assuming a decent receiver anyway, and the one he has should be fairly good. That's one reason why I say if the background noise increases when connecting the antenna, it should be good enough. If it doesn't, there could be a problem. But it will take a really dead antenna system to be like that on HF. Even just sticking a 5 feet piece of wire into the center pin of a decent receiver will cause the noise level to increase, and thus be a fairly viable antenna. Not that it's going to pick up everything, but it should pick up quite a bit. Note the portable SW radios with short whips, etc.. It is also an issue on HF, especially with less expensive receivers. You don't see it on the S-Meter because the meter is set such that the typical receiver noise doesn't show up. But it is there. And it does affect weak signal intelligibility. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
Relationship Between Antenna Efficiency and Received Signal Strength
On Thursday, January 23, 2014 9:45:31 PM UTC-6, Jerry Stuckle wrote:
It is also an issue on HF, especially with less expensive receivers. You don't see it on the S-Meter because the meter is set such that the typical receiver noise doesn't show up. But it is there. And it does affect weak signal intelligibility. I didn't say that internal receiver noise would show on the S meter. I suppose it's possible receiver noise could effect weak signal reception on HF, but it's going to have to be a really low level not to override the internal receiver noise on any modern radio, unless it's some kind of abnormal birdy or whatever. I just don't see it being a much of a problem on HF, particularly 20m. If external noise or signals picked up by the antenna don't override the internal receiver noise on 20m, something is broke somewhere. And if the system is that broke, might as well forget anyone hearing him, particularly running QRP. :( He should do OK with a small loop as long as it's built and working right. |
Relationship Between Antenna Efficiency and Received Signal Strength
On Wednesday, January 22, 2014 7:32:09 PM UTC-6, Jeff Liebermann wrote:
You're not radiating anything in receive. Isn't part of the received signal re-radiated? -- 73, Cecil, w5dxp.com |
Relationship Between Antenna Efficiency and Received Signal Strength
On 1/24/2014 6:40 AM, wrote:
On Thursday, January 23, 2014 9:45:31 PM UTC-6, Jerry Stuckle wrote: It is also an issue on HF, especially with less expensive receivers. You don't see it on the S-Meter because the meter is set such that the typical receiver noise doesn't show up. But it is there. And it does affect weak signal intelligibility. I didn't say that internal receiver noise would show on the S meter. I suppose it's possible receiver noise could effect weak signal reception on HF, but it's going to have to be a really low level not to override the internal receiver noise on any modern radio, unless it's some kind of abnormal birdy or whatever. I just don't see it being a much of a problem on HF, particularly 20m. If external noise or signals picked up by the antenna don't override the internal receiver noise on 20m, something is broke somewhere. And if the system is that broke, might as well forget anyone hearing him, particularly running QRP. :( He should do OK with a small loop as long as it's built and working right. Low antenna efficiency affects not only the received signal, but the received noise. And yes, many inexpensive "modern" receivers suffer from poor front ends. And since transistors (especially bipolar) typically generate more noise than tubes, noise can be a worse problem now than in the 60's. You can get low noise transistors, but these are more expensive. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
Relationship Between Antenna Efficiency and Received Signal Strength
On 1/24/2014 2:38 AM, Jeff wrote:
I'm sorry Jerry, but you don't know what you are talking about. Smith Charts do not have anything to do with antenna efficiency or resonance. The only thing that Smith Charts does is explain what is happening inside of a piece of coax X inches long. Note I do not use feet - since that is too vague. Whilst I agree with your first point, Smiths Charts do not "explain what is happening inside of a piece of coax X inches long". They are an easy way to plot impedances, and show what happens if you *change* the length of coax, but more importantly they give you an easy way of working out how to match impedances (with or without any length of coax involved). They can also display other valuable quantities such as Q. jeff They do if you know how to use them properly. For instance, they will tell you when the reactive portion of the impedance is zero (neither capacitive nor inductive), which indicates resonance. They will also tell you the antenna's impedance at a specific frequency. Both can be used to indirectly determine antenna efficiency. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
Relationship Between Antenna Efficiency and Received Signal Strength
"Jerry Stuckle" wrote in message ... And yes, many inexpensive "modern" receivers suffer from poor front ends. And since transistors (especially bipolar) typically generate more noise than tubes, noise can be a worse problem now than in the 60's. You can get low noise transistors, but these are more expensive. -- How did ou come up with transistors generate more noise than tubes ? Most of my research into low noise has been above 50 mhz and the beter tubes generate much more noise than transistors. The older U310 devices have a noise figure less than 2 db at 150 mhz and a 6cw4 will have around 3 db. Cheap gaasfets have noise figuers less than 1 db. 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. --- 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 04:06:20 -0800 (PST), W5DXP
wrote: On Wednesday, January 22, 2014 7:32:09 PM UTC-6, Jeff Liebermann wrote: You're not radiating anything in receive. Isn't part of the received signal re-radiated? I have no idea. I guess it's possible for a received signal to "bounce" off the wire and wander off elsewhere. With VSWR, the reflected signal might be re-radiated if the source impedance is mismatched. Dunno. -- 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 ... Isn't part of the received signal re-radiated? I have no idea. I guess it's possible for a received signal to "bounce" off the wire and wander off elsewhere. With VSWR, the reflected signal might be re-radiated if the source impedance is mismatched. Dunno. Interisting thought. When the signal hits the receiver I am sure there is some mismatch and part of it is reflected back to the antenna. Now what hapens. All of it is radiated, part radiated and part reflected back, all of it reflected back to the receiver ? --- 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 1/24/2014 10:58 AM, Ralph Mowery wrote:
"Jerry Stuckle" wrote in message ... And yes, many inexpensive "modern" receivers suffer from poor front ends. And since transistors (especially bipolar) typically generate more noise than tubes, noise can be a worse problem now than in the 60's. You can get low noise transistors, but these are more expensive. -- How did ou come up with transistors generate more noise than tubes ? Almost 50 years of experience, including studying both tubes and transistors in my EE courses back in the 70's. Plus measurements of both received and transmitted signals, using lab-grade test equipment. 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. 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. Most of my research into low noise has been above 50 mhz and the beter tubes generate much more noise than transistors. The older U310 devices have a noise figure less than 2 db at 150 mhz and a 6cw4 will have around 3 db. Cheap gaasfets have noise figuers less than 1 db. 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. 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. 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. 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. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
Relationship Between Antenna Efficiency and Received Signal Strength
It seems to me to be the same as a multipath TV signal causing
ghosting. The signal that is not on the direct path hits a building and is reradiated and arrives at the TV at a different time. ....and how about the reflectors and directors on a Yagi antenna? ....where does the signal go when it hits something? It is either absorbed or re-radiated -- some of course is lost in heating, but there is always a little left over. Food for thought! Irv VE6BP -- Political correctness is a doctrine, fostered by a delusional, illogical minority, and rapidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a piece of **** by the clean end. |
Relationship Between Antenna Efficiency and Received Signal Strength
Jeff wrote:
I'm sorry Jerry, but you don't know what you are talking about. Smith Charts do not have anything to do with antenna efficiency or resonance. The only thing that Smith Charts does is explain what is happening inside of a piece of coax X inches long. Note I do not use feet - since that is too vague. Whilst I agree with your first point, Smiths Charts do not "explain what is happening inside of a piece of coax X inches long". They are an easy way to plot impedances, and show what happens if you *change* the length of coax, but more importantly they give you an easy way of working out how to match impedances (with or without any length of coax involved). They can also display other valuable quantities such as Q. jeff A Smith chart is a plot of reactance and resistance versus frequency and can be used for just about anything, if you know how to use one. In the case of an antenna, the chart shows what you have to match at any particular frequency and the resonant frequency of the antenna, i.e. the point where the reactance is zero. -- Jim Pennino |
Relationship Between Antenna Efficiency and Received Signal Strength
On Fri, 24 Jan 2014 04:06:20 -0800 (PST), W5DXP
wrote: On Wednesday, January 22, 2014 7:32:09 PM UTC-6, Jeff Liebermann wrote: You're not radiating anything in receive. Isn't part of the received signal re-radiated? I have no idea. I guess it's possible for a received signal to "bounce" off the wire and wander off elsewhere. With VSWR, the reflected signal might be re-radiated if the source impedance is mismatched. Dunno. My recollection is that in the best of cases (good match, no dissipative losses), half of the RF energy which impinges on the antenna goes into the feedline. The other half is re-radiated. AIUI, the received EM field induces a current flow in the antenna... and this current flow itself causes another EM field to be generated and radiated away. |
Relationship Between Antenna Efficiency and Received Signal Strength
"Jerry Stuckle" wrote in message ... How did ou come up with transistors generate more noise than tubes ? Almost 50 years of experience, including studying both tubes and transistors in my EE courses back in the 70's. Plus measurements of both received and transmitted signals, using lab-grade test equipment. 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. 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. I think you are mixing apples and oranges. For transmiters the tubes usually have less broad band noise. One reason is not the tube, but the tuned circuits are much more selective. With the high impedance of the tubes it is easy to be very selective due to the circuit Q. For a receiver, it is still all about the noise figuer and having enough gain (which is not usually a problem) to overcome the noise of the other parts of the receiver. Yes, you could run the CAP repeater with seperate antennas with tubes where you could not with the transistors. As above the circuit selectivity has alot to do with it. Tube circuits are much more selective when it comes to broad band noise. Many transistor receivers are broad band in the first few RF stages. That gives two problems to over come. Broad band noise for the transmitter (which I am not talking about) and the broad RF stages of the receiver (Not noise of the transistor/fet but poor selectivity). The old GE Mastr ll is one of the few that has a fairly narrow front end. I have one of those on 2 meters. What do you call relative expensive for a transistor/fet that has a noise figuer of around 1 db ? Even in some of the old ARRL repeater handbooks they are putting fet preamps ahead of the tube receivers. What tubes are you talking about that has an under 2 db noise figuer at 150 mhz ? I think there was a 417 and maybe a 416 that might make it, but they were very expensive, especially the 416. --- 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 1:22:02 PM UTC-6, David Platt wrote:
My recollection is that in the best of cases (good match, no dissipative losses), half of the RF energy which impinges on the antenna goes into the feedline. The other half is re-radiated. That is my recollection also. 73, Cecil, w5dxp.com |
Relationship Between Antenna Efficiency and Received Signal Strength
On 1/24/2014 2:24 PM, Ralph Mowery wrote:
"Jerry Stuckle" wrote in message ... How did ou come up with transistors generate more noise than tubes ? Almost 50 years of experience, including studying both tubes and transistors in my EE courses back in the 70's. Plus measurements of both received and transmitted signals, using lab-grade test equipment. 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. 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. I think you are mixing apples and oranges. For transmiters the tubes usually have less broad band noise. One reason is not the tube, but the tuned circuits are much more selective. With the high impedance of the tubes it is easy to be very selective due to the circuit Q. For a receiver, it is still all about the noise figuer and having enough gain (which is not usually a problem) to overcome the noise of the other parts of the receiver. No, I am not mixing apples and oranges. Sure, the transmitter tuned circuits have a higher Q, but that does not affect noise on nearby frequencies (like 4.25Mhz apart on 2 meters - less than 3% of the transmitted frequency). Remember also that receivers also have tuned circuits for input; many of the older receivers had preselectors to tune the input to the desired frequency (and these circuits typically had higher Q than transmitter output circuits). Yes, you could run the CAP repeater with seperate antennas with tubes where you could not with the transistors. As above the circuit selectivity has alot to do with it. Tube circuits are much more selective when it comes to broad band noise. Many transistor receivers are broad band in the first few RF stages. That gives two problems to over come. Broad band noise for the transmitter (which I am not talking about) and the broad RF stages of the receiver (Not noise of the transistor/fet but poor selectivity). The old GE Mastr ll is one of the few that has a fairly narrow front end. I have one of those on 2 meters. No, tubes themselves generate less noise, especially when running in a non-linear mode such as Class C. But transistors definitely generate more noise, as can be identified on a good spectrum analyzer. What do you call relative expensive for a transistor/fet that has a noise figuer of around 1 db ? For manufacturers, anything over a couple of cents per device. But also GAsFETs are also more susceptible to static charges from the antenna, requiring additional protective circuitry at the front end. Even in some of the old ARRL repeater handbooks they are putting fet preamps ahead of the tube receivers. Yes, and they also put tube preamps in front of the tube receivers. FETs were real popular back then, mainly because they weren't tubes - and didn't have the high power requirements associated. They also were new, making them ripe for experimentation (quite popular at one time). What tubes are you talking about that has an under 2 db noise figuer at 150 mhz ? I think there was a 417 and maybe a 416 that might make it, but they were very expensive, especially the 416. I don't remember tube numbers any more - that was over 40 years ago, and I haven't touched a receiver tube circuit in at least 30 years But I also remember having to design low noise RF circuits - and make them work. Not easy to do even in the lab; much harder for manufacturers. And when we were doing solid state amplifiers, it was much harder to get a great noise figure. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
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
On 1/24/2014 5:10 PM, wrote:
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 my point was - the overall level may NOT be overriding the receiver's internal noise. And to be perfectly accurate, ANY lowering of the external signal decreases the S/N ratio because the internally generated noise does not change. But I also understand what you're getting at. 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. Yes, most current ham rigs are that good (at least I don't know of any which aren't). But a lot of less expensive general coverage ("SWL") receivers aren't. -- ================== 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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