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#1
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Low Noise receiving Loop antenna
My neighborhood is loaded with some kind of electrical noise which makes
working 160 & 75 meters difficult. I have tried to locate the source but have come up empty at this point. It appears to be something other than power line noise which may mean its coming from someones house. I was hoping the solution to the problem was to build a low noise receiving loop antenna. Well, the noise is mostly gone..........but so are the signals.....even when I use a preamp. I have tried an ICE 75 meter preamp and a KD9SV 160/75 meter preamp. Still the noise is gone but the signals are really weak, if I hear anything at all. Not sure what if anything I did is wrong or if I am expecting too much from this loop or the preamps don't have enough gain to make this work. Anyone familiar enough with receiving loops to be able to assist me in figuring out whats wrong here? TIA Tony |
#2
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Low Noise receiving Loop antenna
On Sat, 17 Nov 2007 07:36:28 -1000, Tony Giacometti
wrote: Anyone familiar enough with receiving loops to be able to assist me in figuring out whats wrong here? Hi Tony, There is no such thing as a Low Noise antenna (loop or otherwise). Given that what you build is deaf, that should be a reality check of this presumed quality of the antenna. Well, actually, you built it wrong. However, building it right stands only a partial chance of lowering noise, and not because the antenna has some remarkable quality that is not otherwise found in the plug ordinary dipole. In that sense, the reduction of noise would only follow turning the dipole (or loop, same thing) until the source of that noise fell into a null. This is the conventional method of employing a "Low Noise" antenna. Let me guess. It is a shielded loop. You forgot to leave a gap in the shield. 73's Richard Clark, KB7QHC |
#3
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Low Noise receiving Loop antenna
Richard Clark wrote:
On Sat, 17 Nov 2007 07:36:28 -1000, Tony Giacometti wrote: Anyone familiar enough with receiving loops to be able to assist me in figuring out whats wrong here? Hi Tony, There is no such thing as a Low Noise antenna (loop or otherwise). Given that what you build is deaf, that should be a reality check of this presumed quality of the antenna. Well, actually, you built it wrong. However, building it right stands only a partial chance of lowering noise, and not because the antenna has some remarkable quality that is not otherwise found in the plug ordinary dipole. In that sense, the reduction of noise would only follow turning the dipole (or loop, same thing) until the source of that noise fell into a null. This is the conventional method of employing a "Low Noise" antenna. Let me guess. It is a shielded loop. You forgot to leave a gap in the shield. 73's Richard Clark, KB7QHC it is a shielded loop and no the gap is there, thats why I am wondering why its not doing what I thought it would do. |
#4
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Low Noise receiving Loop antenna
On Sat, 17 Nov 2007 09:07:58 -1000, Tony Giacometti
wrote: Let me guess. It is a shielded loop. You forgot to leave a gap in the shield. it is a shielded loop and no the gap is there, thats why I am wondering why its not doing what I thought it would do. Hi Tony, It is working perfectly! It is working exactly as it was constructed. You got your plans from the wrong source (or misread them, or failed to follow directions). There are several ways to construct one correctly, so I won't go into those variations. There is probably a fix to the one you have, but that is shooting in the dark. Let's simply investigate the quality you seek. Low Noise comes only from the antenna's quality of yielding the best dipole performance possible under the circumstances. As these circumstances often involve use in the low frequencies, the traditional high elevation long-wire dipole is usually not an option. Further, if it is, it rarely allows for rotation. What is usually within the user's skill or available space renders a dipole that suffers from the proximity of "things." These "things" disrupt the balance, and hence the directionality of the dipole; thus noise sensitivity rises (noise fills in through what should have been nulls in the dipole pattern). The user still cannot turn the dipole and thus the long-wire in the garden is a mediocre performer at best, and is usually a disappointment all around. Enter the loop. The traditional loop for low frequency use is in fact quite small. By being small it suffers less in relation to the proximity of "things." This, of course, is if you erect it in the same place as that long-wire disappointment you tugged down. That is, the loop improves only in comparison; fortunately, it also brings the virtue of being rotatable. That would be enough, but the snake oil salesmen like to guild the Lily. Enter the shielded loop. The shielded loop solves a problem, certainly. That is the problem of balance. However, if you use careful crafting of a simple loop, you don't have any problem to solve. There are many other details to sort out. That can be left to other correspondence. 73's Richard Clark, KB7QHC |
#5
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Low Noise receiving Loop antenna
Richard Clark wrote:
On Sat, 17 Nov 2007 09:07:58 -1000, Tony Giacometti wrote: Let me guess. It is a shielded loop. You forgot to leave a gap in the shield. it is a shielded loop and no the gap is there, thats why I am wondering why its not doing what I thought it would do. Hi Tony, It is working perfectly! It is working exactly as it was constructed. You got your plans from the wrong source (or misread them, or failed to follow directions). There are several ways to construct one correctly, so I won't go into those variations. There is probably a fix to the one you have, but that is shooting in the dark. Let's simply investigate the quality you seek. Low Noise comes only from the antenna's quality of yielding the best dipole performance possible under the circumstances. As these circumstances often involve use in the low frequencies, the traditional high elevation long-wire dipole is usually not an option. Further, if it is, it rarely allows for rotation. What is usually within the user's skill or available space renders a dipole that suffers from the proximity of "things." These "things" disrupt the balance, and hence the directionality of the dipole; thus noise sensitivity rises (noise fills in through what should have been nulls in the dipole pattern). The user still cannot turn the dipole and thus the long-wire in the garden is a mediocre performer at best, and is usually a disappointment all around. Enter the loop. The traditional loop for low frequency use is in fact quite small. By being small it suffers less in relation to the proximity of "things." This, of course, is if you erect it in the same place as that long-wire disappointment you tugged down. That is, the loop improves only in comparison; fortunately, it also brings the virtue of being rotatable. That would be enough, but the snake oil salesmen like to guild the Lily. Enter the shielded loop. The shielded loop solves a problem, certainly. That is the problem of balance. However, if you use careful crafting of a simple loop, you don't have any problem to solve. There are many other details to sort out. That can be left to other correspondence. 73's Richard Clark, KB7QHC Richard, I use a vertical antenna, for transmitting its great, does a fine job, but for receive, with the noise in the neighborhood, its not the best option. I have tried to use an ANC-4 noise reducer but the noise isn't reduced enough to hear the weaker signals. So, what to do, I followed the instructions for building the loop from W2YR and KN4LF and from this link http://www.hard-core-dx.com/nordicdx.../coaxloop.html As I wrote previous I have 2 good preamps but the signals are still very weak. Have you ever built one of these? If so, did you experience the same problem? I don't have room for a beverage but if I am unable to solve this loop issue I will probably have to consider a K9AY array which will force me to move other antennas around on my 1/3rd of an acre. |
#6
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Low Noise receiving Loop antenna
On Sat, 17 Nov 2007 10:30:06 -1000, Tony Giacometti
wrote: Richard, I use a vertical antenna, for transmitting its great, does a fine job, but for receive, with the noise in the neighborhood, its not the best option. I have tried to use an ANC-4 noise reducer but the noise isn't reduced enough to hear the weaker signals. Hi Tony, Leaving that aside for others to comment.... So, what to do, I followed the instructions for building the loop from W2YR and KN4LF and from this link http://www.hard-core-dx.com/nordicdx.../coaxloop.html There is a world of opportunity in making a mistake with this monster. It goes a long way to do something difficult that could be done vastly easier. As I wrote previous I have 2 good preamps but the signals are still very weak. You state that there is no gap. The page you supply clearly shows gaps at the top of the two loops. Anything you hear is a function of the poor shielding. By your description of your construction, you shouldn't be able to hear anything at all! Have you ever built one of these? No, not one of these (there are too many frogs to kiss them all). I don't have room for a beverage but if I am unable to solve this loop issue I will probably have to consider a K9AY array which will force me to move other antennas around on my 1/3rd of an acre. A solution is vastly simpler than that - and you can still build a loop. Google for more designs and submit them here for review (the one you provided rates low on the sanity scale). 73's Richard Clark, KB7QHC |
#7
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Low Noise receiving Loop antenna
Tony Giacometti wrote in
news:VvSdnQC_g_Sb0qLanZ2dnUVZ_hKdnZ2d@hawaiiantel. net: So, what to do, I followed the instructions for building the loop from W2YR and KN4LF and from this link http://www.hard-core-dx.com/nordicdx.../coaxloop.html I think you are describing a scenario where, with the loop+preamp, the receiver system is limited by internal noise rather than external noise. So, it is a two band design, and that complicates matters somewhat. Just concentrating on the 160m loop... My calcs are that the 160m loop alone, tuned for zero series reactance (should need ~90pF) and loaded with 50 ohms should have equivalent gain of around -47dBi. You would have to consider the preamp NF and gain and receiver NF to evaluate the system noise floor, and you haven't given those details (though they may be implied... but I am not familiar with the preamp you are using). Without using a preamp, the external noise (based on ITU-R P.372-8 Residiential man made noise) with this loop ought be of about the same magnitude as the internal noise of a good transceiver, give or take. For a preamp to improve the situation, it would need a NF significantly better than the transceiver and sufficient gain to overcome the transceiver noise. Owen |
#8
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Low Noise receiving Loop antenna
Tony Giacometti wrote:
it is a shielded loop and no the gap is there, thats why I am wondering why its not doing what I thought it would do. What you've done is to build a truly shielded loop. The notion that a shield somehow blocks the electric field and lets the magnetic field through is a folk tale -- an intact shield like the one you built blocks both electric and magnetic fields. (Good thing, too, or else coax cable wouldn't do its job.) You've just done an experiment that proves it. The gap in a so-called "shielded loop" provides a path for current outside the "shield" to get inside. The net result is that the outside of the "shield" is just an ordinary loop antenna, and the gap acts like a feedpoint to get the current inside where it can get to the receiver. It responds to normal electric and magnetic fields exactly like an unshielded loop. What the "shield" buys you is improved balance, which helps prevent the feedline from becoming part of the antenna and picking up local noise which you can null out if balance is good. Roy Lewallen, W7EL |
#9
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Low Noise receiving Loop antenna
Richard Clark wrote:
On Sat, 17 Nov 2007 10:30:06 -1000, Tony Giacometti wrote: Richard, I use a vertical antenna, for transmitting its great, does a fine job, but for receive, with the noise in the neighborhood, its not the best option. I have tried to use an ANC-4 noise reducer but the noise isn't reduced enough to hear the weaker signals. Hi Tony, Leaving that aside for others to comment.... So, what to do, I followed the instructions for building the loop from W2YR and KN4LF and from this link http://www.hard-core-dx.com/nordicdx.../coaxloop.html There is a world of opportunity in making a mistake with this monster. It goes a long way to do something difficult that could be done vastly easier. As I wrote previous I have 2 good preamps but the signals are still very weak. You state that there is no gap. sorry, but maybe I wasn't clear enough, there IS a gap - just like the one in the link. The page you supply clearly shows gaps at the top of the two loops. Anything you hear is a function of the poor shielding. By your description of your construction, you shouldn't be able to hear anything at all! Have you ever built one of these? No, not one of these (there are too many frogs to kiss them all). I don't have room for a beverage but if I am unable to solve this loop issue I will probably have to consider a K9AY array which will force me to move other antennas around on my 1/3rd of an acre. A solution is vastly simpler than that - and you can still build a loop. Google for more designs and submit them here for review (the one you provided rates low on the sanity scale). I did do a search for loops of this type and basically they are all the same. I have been told Wellbrook makes good loops, but I don't like the idea of spending $300-$500 for one at this point. 73's Richard Clark, KB7QHC |
#10
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Low Noise receiving Loop antenna
Roy Lewallen wrote in
: Tony Giacometti wrote: it is a shielded loop and no the gap is there, thats why I am wondering why its not doing what I thought it would do. What you've done is to build a truly shielded loop. The notion that a I think you guys are reading this the wrong way. Perhaps it should have been written "it is a shielded loop and no, the gap is there,..." You know people asking questions don't take much care in expression. Owen |
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