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#71
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Low Noise receiving Loop antenna
Owen Duffy wrote:
Tony Giacometti wrote in news:bMednQ1HY8JTVN7anZ2dnUVZ_gGdnZ2d@hawaiiantel. net: ... sorry, I'm not trying to be an ass here but the diagram I have shows 3 connections to the cap. 2 for the loop and one for the center conductor of the feedline. Is my diagram whats confusing the issue? Here is a diagram of what I suggested: http://www.vk1od.net/SmallTunedSquareLoop/index.2.gif . The variable capacitor needs to be 0-400pF. The fixed capacitor should be at least 1000pF. If you couldn't arrive at this circuit from the word description, and you aren't being silly, then it questions whether your intial construction was based on misinterpretation of the original article. Here is an even better idea: http://www.vk1od.net/SmallTunedSquareLoop/index.3.gif . There is only one change here, the inner conductor is bonded to the outer conductor at the left hand side of the shield gap. Ask yourself why that improves things... some will suggest it just halved the loop size, but it hasn't. Owen I understand now, seeing your drawing clears it up for me. No, I wasn't being difficult or silly, I kept thinking of how I have the unit wired and I couldn't picture in my mind (senior moment?) the changes. Anyway now I see what you are asking me to try and I will give this a try. Hopefully tonite after work. I will let you know the results. Thank You. |
#72
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Low Noise receiving Loop antenna
Tony Giacometti wrote in
news:geadnZCVBcuhxdnanZ2dnUVZ_ojinZ2d@hawaiiantel. net: Owen Duffy wrote: Tony Giacometti wrote in news:bMednQ1HY8JTVN7anZ2dnUVZ_gGdnZ2d@hawaiiantel. net: ... sorry, I'm not trying to be an ass here but the diagram I have shows 3 connections to the cap. 2 for the loop and one for the center conductor of the feedline. Is my diagram whats confusing the issue? Here is a diagram of what I suggested: http://www.vk1od.net/SmallTunedSquareLoop/index.2.gif . The variable capacitor needs to be 0-400pF. The fixed capacitor should be at least 1000pF. If you couldn't arrive at this circuit from the word description, and you aren't being silly, then it questions whether your intial construction was based on misinterpretation of the original article. Here is an even better idea: http://www.vk1od.net/SmallTunedSquareLoop/index.3.gif . There is only one change here, the inner conductor is bonded to the outer conductor at the left hand side of the shield gap. Ask yourself why that improves things... some will suggest it just halved the loop size, but it hasn't. Owen I understand now, seeing your drawing clears it up for me. No, I wasn't being difficult or silly, I kept thinking of how I have the unit wired and I couldn't picture in my mind (senior moment?) the changes. Anyway now I see what you are asking me to try and I will give this a try. Hopefully tonite after work. I will let you know the results. Thank You. Tony, Keep in mind this scheme improves the impedance match (ie reduces the mismatch "losses", but it doesn't approach an MPT match unless the fixed capacitor is very large, and in that case bandwidth would probably be too narrow for your use. The trick is to improve the system gain enough to be usable without making the system unusable because it is too narrow. The suggested fixed capacitor of 1000pF should win you enough system gain, if it doesn't try larger values (eg 4,700pF). I will be offline for a few days, I look forward to hearing of the outcome. Owen |
#73
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Low Noise receiving Loop antenna
On Nov 21, 1:10 pm, Owen Duffy wrote:
I understand now, seeing your drawing clears it up for me. No, I wasn't being difficult or silly, I kept thinking of how I have the unit wired and I couldn't picture in my mind (senior moment?) the changes. Anyway now I see what you are asking me to try and I will give this a try. Hopefully tonite after work. I will let you know the results. Thank You. Tony, Keep in mind this scheme improves the impedance match (ie reduces the mismatch "losses", but it doesn't approach an MPT match unless the fixed capacitor is very large, and in that case bandwidth would probably be too narrow for your use. The trick is to improve the system gain enough to be usable without making the system unusable because it is too narrow. The suggested fixed capacitor of 1000pF should win you enough system gain, if it doesn't try larger values (eg 4,700pF). I will be offline for a few days, I look forward to hearing of the outcome. Owen I guess it's worth a shot if the level is really that low. But something seems strange that he would have that problem. Using even my small 16 inch loop, fed using the usual cap in parallel method, I have more signal level than I actually need, even at the upper end of its range. In general if the background noise level peaks, and there is a definite difference between the antenna connected, and unconnected, seems that should be enough signal level. On the recordings I made, I was comparing the 16 inch loop vs full size wire antennas, and the drop in level is really not that drastic. IE: the stations still sound "loud" vs the large wire antennas, and I have pretty decent S meter levels on the loops. I'm tuned to 740 kc AM-BC on my big loop right now and the S meter is reading 40 over 9, and the radio preamp is off. I didn't really notice any level problems on the shielded loops I've tried. But I'm starting to wonder if maybe he might get a higher level just from using a regular solenoid loop. It's also possible the radio could use a tweak.. Which is easy to do on the drake receivers. All the trimmers are on top of the chassis. Don't even need any fancy gear. He can tune for the middle of each band appx, and use the xtal calibrator as the signal to tweak all the trimmers per each band. Of course, you would peak each trimmer for max S meter reading. On the drakes, he should show a pretty healthy S meter reading on the calibrator signal if it's working right. MK |
#74
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Low Noise receiving Loop antenna
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#75
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Low Noise receiving Loop antenna
Owen Duffy wrote:
Tony Giacometti wrote in news:geadnZCVBcuhxdnanZ2dnUVZ_ojinZ2d@hawaiiantel. net: Owen Duffy wrote: Tony Giacometti wrote in news:bMednQ1HY8JTVN7anZ2dnUVZ_gGdnZ2d@hawaiiantel. net: ... sorry, I'm not trying to be an ass here but the diagram I have shows 3 connections to the cap. 2 for the loop and one for the center conductor of the feedline. Is my diagram whats confusing the issue? Here is a diagram of what I suggested: http://www.vk1od.net/SmallTunedSquareLoop/index.2.gif . The variable capacitor needs to be 0-400pF. The fixed capacitor should be at least 1000pF. If you couldn't arrive at this circuit from the word description, and you aren't being silly, then it questions whether your intial construction was based on misinterpretation of the original article. Here is an even better idea: http://www.vk1od.net/SmallTunedSquareLoop/index.3.gif . There is only one change here, the inner conductor is bonded to the outer conductor at the left hand side of the shield gap. Ask yourself why that improves things... some will suggest it just halved the loop size, but it hasn't. Owen I understand now, seeing your drawing clears it up for me. No, I wasn't being difficult or silly, I kept thinking of how I have the unit wired and I couldn't picture in my mind (senior moment?) the changes. Anyway now I see what you are asking me to try and I will give this a try. Hopefully tonite after work. I will let you know the results. Thank You. Tony, Keep in mind this scheme improves the impedance match (ie reduces the mismatch "losses", but it doesn't approach an MPT match unless the fixed capacitor is very large, and in that case bandwidth would probably be too narrow for your use. The trick is to improve the system gain enough to be usable without making the system unusable because it is too narrow. The suggested fixed capacitor of 1000pF should win you enough system gain, if it doesn't try larger values (eg 4,700pF). I will be offline for a few days, I look forward to hearing of the outcome. Owen I tried both configurations, both raised the noise level which I am thinking must be related to the gain you said I would get, I didn't need the preamp at all. I didn't get the nulls like I get from the original loop - that was a mild surprise - there was only a 2-3 S unit difference between noise peak and noise null, The original loop normally has S1-2 99% of the time when nulled. The current loop has a difference between noise peak and noise null of 7-9 S units. Now don't misunderstand me, but I like the low noise level. What concerns me with the other 2 configurations is the gain makes the noise increase so much that I am not so sure I would be able to hear the weaker ones. I think this project as simple as I thought it would be ...... just isn't. What I would like to accomplish with this loop idea is to have the low noise and the ability to null out the noise from my neighbors houses. But at the same time have enough gain to be able to hear the weak signals. Now I don't have preference for using the preamp or not. Whatever works is what I want to go with. Maybe changing the type of loop to a different style of loop would be the way to achive what I would like to obtain. Obviously, there is a miriad of designs and configurations. Since I need the loop only for 75 meters and have a limited amount of real estate this cuts the pile down to a lesser amount. What to do...................well, maybe I should start over - why not try a different type/style of loop. A larger loop might be better for gain but how big before its not able to null out noise cause I can't rotate it due to its size? Does the loop have to be coax? can it be some other type of wire? Your input is much appreciated. |
#76
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Low Noise receiving Loop antenna
Tony Giacometti wrote in
: Owen Duffy wrote: .... I will be offline for a few days, I look forward to hearing of the outcome. Owen I tried both configurations, both raised the noise level which I am thinking must be related to the gain you said I would get, I didn't I take it that 'raise the noise level' actually means you got more noise out of the receiver / higher S meter reading on band noise. need the preamp at all. I didn't get the nulls like I get from the original loop - that was a mild surprise - there was only a 2-3 S unit Neither the preamp, nor the tuning changes you made should change the directivity (ie the pattern, the depth of the nulls) of the antenna. difference between noise peak and noise null, The original loop normally has S1-2 99% of the time when nulled. The current loop has a difference between noise peak and noise null of 7-9 S units. Now don't I have already told you those measurements don't mean anything to me. misunderstand me, but I like the low noise level. What concerns me with the other 2 configurations is the gain makes the noise increase so much that I am not so sure I would be able to hear the weaker ones. If you want to improve the depth of the nulls, you have to concentrate on the balance of the antenna, the symmetry of the loop, its feedline, its environment etc. I think Roy might have said that earlier. I think this project as simple as I thought it would be ...... just isn't. What I would like to accomplish with this loop idea is to have the low noise and the ability to null out the noise from my neighbors houses. But at the same time have enough gain to be able to hear the weak signals. Now I don't have preference for using the preamp or not. Whatever works is what I want to go with. It is fairly simple, you might have needed to learn a bit, but you probably also had to unlearn some stuff. Maybe changing the type of loop to a different style of loop would be the way to achive what I would like to obtain. You have already been told there is no such thing as a low noise antenna. The loop has the advantage of being able to null out signals from two opposite directions, which can help if the interference is predominantly from one (or both) of those directions. You can improve the depth of those nulls, but pattern or directivity is unrelated to the power transfer problem. Obviously, there is a miriad of designs and configurations. Since I need the loop only for 75 meters and have a limited amount of real estate this cuts the pile down to a lesser amount. What to do...................well, maybe I should start over - why not try a different type/style of loop. A larger loop might be better for gain but how big before its not able to null out noise cause I can't rotate it due to its size? Does the loop have to be coax? can it be some other type of wire? Remember that symmetry is key to the depth of the null. If it is harder to build a larger loop with equally good symmetry (including to the environment), you have more gain, but poorer nulls... and your main reason for selecting the loop is for rejection of interference using the nulls. You need adequate gain, and the best balance rather than the other way round. Your input is much appreciated. Thanks 73 Owen |
#77
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Low Noise receiving Loop antenna
Owen Duffy wrote:
Tony Giacometti wrote in : Owen Duffy wrote: ... I will be offline for a few days, I look forward to hearing of the outcome. Owen I tried both configurations, both raised the noise level which I am thinking must be related to the gain you said I would get, I didn't I take it that 'raise the noise level' actually means you got more noise out of the receiver / higher S meter reading on band noise. yes! need the preamp at all. I didn't get the nulls like I get from the original loop - that was a mild surprise - there was only a 2-3 S unit Neither the preamp, nor the tuning changes you made should change the directivity (ie the pattern, the depth of the nulls) of the antenna. I didn't use the preamp for these tests, but the noise level did change and yes, the nulls were not that deep. As I wrote this was a mild surprise and I did recheck all connections and redid the test with the same result. difference between noise peak and noise null, The original loop normally has S1-2 99% of the time when nulled. The current loop has a difference between noise peak and noise null of 7-9 S units. Now don't I have already told you those measurements don't mean anything to me. misunderstand me, but I like the low noise level. What concerns me with the other 2 configurations is the gain makes the noise increase so much that I am not so sure I would be able to hear the weaker ones. If you want to improve the depth of the nulls, you have to concentrate on the balance of the antenna, the symmetry of the loop, its feedline, its environment etc. I think Roy might have said that earlier. yes he did, and I am not sure why the depth of the nulls changed. I think this project as simple as I thought it would be ...... just isn't. What I would like to accomplish with this loop idea is to have the low noise and the ability to null out the noise from my neighbors houses. But at the same time have enough gain to be able to hear the weak signals. Now I don't have preference for using the preamp or not. Whatever works is what I want to go with. It is fairly simple, you might have needed to learn a bit, but you probably also had to unlearn some stuff. true, I had to unlearn some things that most likely floated around for years. Maybe changing the type of loop to a different style of loop would be the way to achive what I would like to obtain. You have already been told there is no such thing as a low noise antenna. The loop has the advantage of being able to null out signals from two opposite directions, which can help if the interference is predominantly from one (or both) of those directions. You can improve the depth of those nulls, but pattern or directivity is unrelated to the power transfer problem. did I misunderstand you, I thought the noise was nullable but at 75 meters the signals were mostly omnidirectional? Or is this one of the unlearned things? Obviously, there is a miriad of designs and configurations. Since I need the loop only for 75 meters and have a limited amount of real estate this cuts the pile down to a lesser amount. What to do...................well, maybe I should start over - why not try a different type/style of loop. A larger loop might be better for gain but how big before its not able to null out noise cause I can't rotate it due to its size? Does the loop have to be coax? can it be some other type of wire? Remember that symmetry is key to the depth of the null. If it is harder to build a larger loop with equally good symmetry (including to the environment), you have more gain, but poorer nulls... and your main reason for selecting the loop is for rejection of interference using the nulls. You need adequate gain, and the best balance rather than the other way round. Your input is much appreciated. Thanks 73 Owen Ok, I want to build a larger loop to get more gain, if possible deep nulls for reducing local noise, I would like to try wire instead of coax. I want to mount it on a PVC pipe frame. Can you give me any ideas as to what shape and size? Whats a solenoid loop? |
#78
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Low Noise receiving Loop antenna
Tony Giacometti wrote in
: Owen Duffy wrote: .... You have already been told there is no such thing as a low noise antenna. The loop has the advantage of being able to null out signals from two opposite directions, which can help if the interference is predominantly from one (or both) of those directions. You can improve the depth of those nulls, but pattern or directivity is unrelated to the power transfer problem. did I misunderstand you, I thought the noise was nullable but at 75 meters the signals were mostly omnidirectional? Or is this one of the unlearned things? Keep in mind that noise from very close sources can be much stronger than the aggregated noise from more distant source. If you live in a street where everyone has the same noisy plasma TV, the noise from your own one is likely to be much stronger than the aggregate of the others... think through the propagation mechanism and especially the effects where the source is in the near field (say within a quarter wave of your antenna). You can't do much to null the noise from a hundred TVs spread around the neighborhood, but you can null the noise from a close by dominant source like your own, or immediate neighbor's. Of course, in nulling the noise in that direction you also null signals from the same direction. Fortunately, lots of signals come via an ionospheric path (a higher angle), and the null of the loop is normally oriented horizontally so it doesn't knock the ionospheric signals down as much. If you try something beside a shielded loop, make sure you use an effective means of isolating the feed line from the loop so that pickup on the feedline does not feed the receiver. Perhaps by solenoid loop you mean a multi turn loop. A multiturn loop is another way of increasing induced voltage, but it increases the source impedance and you have to solve the impedance matching issue. .... Ok, I want to build a larger loop to get more gain, if possible deep nulls for reducing local noise, I would like to try wire instead of coax. I want to mount it on a PVC pipe frame. Can you give me any ideas as to what shape and size? Whats a solenoid loop? You started of with a loop that was too insensitive, so you have improved that with better matching solving that problem. You can increase the gain by further improvement of the matching... but you don't need more gain than sufficient to have the band noise swamp the receiver internal noise. I know you are convinced that matching also degraded the pattern. If the matching network was entirely inside an effectively shielded box, it should not affect the nulls. Make sure that you retained the shielded loop properly. Why do you still think that a larger loop has deeper nulls. Owen |
#79
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Low Noise receiving Loop antenna
Owen Duffy wrote:
. . . If you try something beside a shielded loop, make sure you use an effective means of isolating the feed line from the loop so that pickup on the feedline does not feed the receiver. . . . In my limited experience, it's extremely difficult or impossible to do a good job of isolating the feedline from a small loop. The common mode impedance is just too high. Roy Lewallen, W7EL |
#80
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Low Noise receiving Loop antenna
Roy Lewallen wrote in
: Owen Duffy wrote: . . . If you try something beside a shielded loop, make sure you use an effective means of isolating the feed line from the loop so that pickup on the feedline does not feed the receiver. . . . In my limited experience, it's extremely difficult or impossible to do a good job of isolating the feedline from a small loop. The common mode impedance is just too high. Roy Lewallen, W7EL Hello Roy, I have a small loop with inexpesive voltage balun, and it gives a quite deep null (though I can't put dB figures on it off hand), and very sharp null. I wonder if the reason that Tony perceives that the nulls are shallow is that he is assessing it on band noise. If so Tony, you should assess the depth of the nulls on a local (ie low elevation) point source that is much stronger than band noise. The test signal should dominate the receiver. If an antenna with deep nulls doesn't reduce band noise much, it suggests that the noise is not mainly from a single direction... as discussed earlier in this thread. Owen |
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