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Shielded loop for RCVR
Over the weekend I cobbled one of these together
http://www.greertech.com/hfloop/mymagloop.html and was rather pleased with the results. My version was made on a scrap wood hexangonal armature which allowed approimately 15' 4" total loop circumference of salvaged RG58/u. It took just over an hour to build, start to finish. I tested it mounted on the roof of my camper van feeding a Sat800. With my Barker and Williamson VR300 pi section tuner it has a frequency range from about 2.3 Mhz up to somewhere around 26 Mhz...in short all of the usual shortwave frequencies of interest. The tuning is fairly sharp in all frerquency ranges, but not so much so as to be touchy. The Sat800 seems to have ample sensitivity to make up for the difference of strength compared to the high long wire I usually use. The most dramatic effect is the quiet! The noise floor usually runs about S4 on the meter with the high long wire, but was reduced to a barely registering S1 with the sheilded loop. An S6 signal is completely in the clear. There is usually a band of RF garbage in my neighborhood extending from about 17 Mhz up to about 23 Mhz which normally obliterates the 15 and 13 meter bands. With the shielded loop this was very much reduced...there wasn't a lot of activity on these bands at the hours I was listening. I never heard WWV at 20 Mhz but did hear one broadcaster in 13M band and some CW on 15. I'm taking the van on vacation to the Shenandoah region next week, will try this antenna out in the field, nd give further impressions when I get back. AR de KC2LVQ |
William:
Look carefully at what you wrote. Couldn't you have achieved the same results by turning the RF gain down, or shortening your existing antenna? Noise down, signals down also? WWV gone? Hmmm. Suspicious. -- Crazy George Remove N O and S P A M imbedded in return address "William Mutch" wrote in message ell.edu... Over the weekend I cobbled one of these together http://www.greertech.com/hfloop/mymagloop.html and was rather pleased with the results. My version was made on a scrap wood hexangonal armature which allowed approimately 15' 4" total loop circumference of salvaged RG58/u. It took just over an hour to build, start to finish. I tested it mounted on the roof of my camper van feeding a Sat800. With my Barker and Williamson VR300 pi section tuner it has a frequency range from about 2.3 Mhz up to somewhere around 26 Mhz...in short all of the usual shortwave frequencies of interest. The tuning is fairly sharp in all frerquency ranges, but not so much so as to be touchy. The Sat800 seems to have ample sensitivity to make up for the difference of strength compared to the high long wire I usually use. The most dramatic effect is the quiet! The noise floor usually runs about S4 on the meter with the high long wire, but was reduced to a barely registering S1 with the sheilded loop. An S6 signal is completely in the clear. There is usually a band of RF garbage in my neighborhood extending from about 17 Mhz up to about 23 Mhz which normally obliterates the 15 and 13 meter bands. With the shielded loop this was very much reduced...there wasn't a lot of activity on these bands at the hours I was listening. I never heard WWV at 20 Mhz but did hear one broadcaster in 13M band and some CW on 15. I'm taking the van on vacation to the Shenandoah region next week, will try this antenna out in the field, nd give further impressions when I get back. AR de KC2LVQ |
"Crazy George" wrote in message ... William: Look carefully at what you wrote. Couldn't you have achieved the same results by turning the RF gain down, or shortening your existing antenna? Noise down, signals down also? WWV gone? Hmmm. Suspicious. I'll answer for him, ...No and No. Receiving loops aren't about signal strength they're about improved Signal to Noise **Ratio**. Not hearing 20 MHz WWV at the hours he said he was listening (late eve?) means nothing as that band folds late at night or propagation simply may not have been favoring a path between them at that time. Try some Google-searching for receiving loops, lots of info. XC |
On Tue, 13 Jul 2004 10:56:16 -0400, - XC - hath writ:
"Crazy George" wrote in message ... William: Look carefully at what you wrote. Couldn't you have achieved the same results by turning the RF gain down, or shortening your existing antenna? Noise down, signals down also? WWV gone? Hmmm. Suspicious. I'll answer for him, ...No and No. Receiving loops aren't about signal strength they're about improved Signal to Noise **Ratio**. And, receiving loops are about nulling out interfering signals. Deep nulls has a loop. Jonesy -- | Marvin L Jones | jonz | W3DHJ | linux | Gunnison, Colorado | @ | Jonesy | OS/2 __ | 7,703' -- 2,345m | config.com | DM68mn SK |
XC wrote,
I'll answer for him, ...No and No. Receiving loops aren't about signal strength they're about improved Signal to Noise **Ratio**. They are? How do they do that? 73, Tom Donaly, KA6RUH |
On Tue, 13 Jul 2004 10:56:16 -0400, "- XC -" wrote:
"Crazy George" wrote in message ... William: Look carefully at what you wrote. Couldn't you have achieved the same results by turning the RF gain down, or shortening your existing antenna? Noise down, signals down also? WWV gone? Hmmm. Suspicious. I'll answer for him, ...No and No. Receiving loops aren't about signal strength they're about improved Signal to Noise **Ratio**. Not hearing 20 MHz WWV at the hours he said he was listening (late eve?) means nothing as that band folds late at night or propagation simply may not have been favoring a path between them at that time. Try some Google-searching for receiving loops, lots of info. XC Dumb question: how do you reduce noise without reducing the strength of the signals you want to hear? How does the antenna know which is which? What makes some antennas "quiet." Bob k5qwg |
A loop has directivity but if the noise is from the same direction as the
desired signal it doesn't help. However if the noise is 90 degrees off then a loop will help. -- 73 Hank WD5JFR "Bob Miller" wrote in message ... On Tue, 13 Jul 2004 10:56:16 -0400, "- XC -" wrote: "Crazy George" wrote in message ... William: Look carefully at what you wrote. Couldn't you have achieved the same results by turning the RF gain down, or shortening your existing antenna? Noise down, signals down also? WWV gone? Hmmm. Suspicious. I'll answer for him, ...No and No. Receiving loops aren't about signal strength they're about improved Signal to Noise **Ratio**. Not hearing 20 MHz WWV at the hours he said he was listening (late eve?) means nothing as that band folds late at night or propagation simply may not have been favoring a path between them at that time. Try some Google-searching for receiving loops, lots of info. XC Dumb question: how do you reduce noise without reducing the strength of the signals you want to hear? How does the antenna know which is which? What makes some antennas "quiet." Bob k5qwg |
OH, for Pete's sake. Loops are sensitive to the H vector. Wires receive
the E vector. Most near field noise tends to be predominantly E field. But, that seems to only be effective up to 3 or 4 MHz, due to the wavelength factor, i. e. the near field shrinks as you go higher in frequency. Fully formed far field wavefronts of noise sources will be just like wanted signals, and unless some polarization difference is available, then directivity is the only way to improve S/N. Only in special circumstances can you see much improvement above 5 MHz due to near field/far field differentiation. But, my point was that no improvement in S/N was reported in the original post. Only a decrease of noise accompanied by a decrease in signal. No relative comparison offered. Are we supposed to *assume* that the signals went down due to time of day, while the noise went down because it is a loop? Maybe the opposite is true? Not enough data to prove either. -- Crazy George Remove N O and S P A M imbedded in return address |
But, that seems to only be effective up to 3 or 4 MHz, due to the wavelength factor, i. e. the near field shrinks as you go higher in frequency. REALLY? How does it do that? W4ZCB |
Bob Miller wrote:
Dumb question: how do you reduce noise without reducing the strength of the signals you want to hear? How does the antenna know which is which? Beams seem to "know" how to receive a signal from one direction while ignoring noise from the opposite direction. My horizontal dipole seems to "know" how to ignore vertically polarized noise. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Say, for purposes of illustration, that the near field ends at 1 wavelength.
At 2 MHz, that is very roughly 530 feet . At 14 MHz it is about 64 feet. At 30 MHz, it has shrunk to ~32 feet. -- Crazy George Remove N O and S P A M imbedded in return address "Harold E. Johnson" wrote in message news:Qf_Ic.82101$Oq2.21575@attbi_s52... But, that seems to only be effective up to 3 or 4 MHz, due to the wavelength factor, i. e. the near field shrinks as you go higher in frequency. REALLY? How does it do that? W4ZCB |
"Crazy George" wrote in message ... Say, for purposes of illustration, that the near field ends at 1 wavelength. At 2 MHz, that is very roughly 530 feet . At 14 MHz it is about 64 feet. At 30 MHz, it has shrunk to ~32 feet. -- Why would the near field end at 1 wavelength? It ends when the wave front arriving at the receiving antenna becomes planar. ie, to function efficiently in the far field, the receiving antenna needs to intercept a planar wavefront. That is, the individual rays need to be arriving in parallel. If the distance between antennas is very great, that is very nearly the case. If the capture area of the receiving antenna is great relative to the distance to the source, the received energy arrives as non parallel rays that basically reach the receiving antenna out of phase with each other and partially cancel. So, the gain of antennas measured in the "near field", where the received energy is not a planar wavefront, will be in error. The distance to the end of the near field is highly dependent on the gain of the antenna and with UHF and SHF antennas often exhibiting very high gain, their near fields can be and often are very large. The power collected by a receiving antenna within the transmitters near field is very nearly constant with distance. In the far field, recovered power varies inversely with the square of the distance. Regards W4ZCB |
Harold E. Johnson wrote,
It ends when the wave front arriving at the receiving antenna becomes planar. ie, to function efficiently in the far field, the receiving antenna needs to intercept a planar wavefront. That is, the individual rays need to be arriving in parallel. If the distance between antennas is very great, that is very nearly the case. If the capture area of the receiving antenna is great relative to the distance to the source, the received energy arrives as non parallel rays that basically reach the receiving antenna out of phase with each other and partially cancel. So, the gain of antennas measured in the "near field", where the received energy is not a planar wavefront, will be in error. The distance to the end of the near field is highly dependent on the gain of the antenna and with UHF and SHF antennas often exhibiting very high gain, their near fields can be and often are very large. Balanis divides the near-field region into two parts: a reactive near-field R0.62 square root(D^3/Lambda) where D is the largest antenna dimension, Lambda is the wavelength, and R is the distance from the antenna surface, and a radiating near-field region R2D^2/Lambda. The far-field he defines as anything greater than 2D^2/Lambda. He gives exceptions to these rules, so take them with a grain of salt. 73, Tom Donaly, KA6RUH |
Cecil wrote,
Bob Miller wrote: Dumb question: how do you reduce noise without reducing the strength of the signals you want to hear? How does the antenna know which is which? Beams seem to "know" how to receive a signal from one direction while ignoring noise from the opposite direction. My horizontal dipole seems to "know" how to ignore vertically polarized noise. -- 73, Cecil http://www.qsl.net/w5dxp Yes, but does your small, inefficient, shielded loop improve the signal-to-noise ratio in the directions of its maximum gain over say, a non shielded loop? Moreover, how do you get your beam to be less sensitive to noise in its favored direction? Are you robbing Peter to pay Paul? 73, Tom Donaly, KA6RUH |
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Hi William, All,
As is common with comparisons, the problems arise due to the shifting sand these arguments are built upon. On Wed, 14 Jul 2004 12:09:17 -0400, William Mutch wrote: But, my point was that no improvement in S/N was reported in the original post. True; I didn't report it but it is there. Typically at most frequencies the desired signal is reduced 1 to 2 S-units with respect to the whip antenna (strong ones) or my high long wire weaker signal...156 feet AWG 16 up 45 feet fed off center w/ a 4:1 balun) but the noise level is reduced by anywhere from 3 to 6 S-units...a very! worthwhile tradeoff. Presumably, the comparison is loop vs. these others. It is not explicit and that is one of the problems of reporting and subsequent interpretation - hence the observation in the double quote above. However, the "issue" is more has anything really changed? A loop (dipole) compared to two verticals. Arguably the so-called off center fed long wire is presumed to be a dipole, however (again poor reporting) nothing says of this antenna being choked. Lacking that choke offers every inducement of Common Modality (the antenna is, after all, fully and admittedly unbalanced by its very description). Common Modality is ever bit a noise hazard as any vertical (is supposed to be - another nightmarish fantasy under the bed). Hence, any perceived boon of noise reduction comes as a consequence of the loop's faithfully performing as a - dipole! Wonders never cease. Exact quantitative measurements are not possible on the Sat800 RCVR because you can't turn off the AGC. I don't know how this got started as a unnecessary evil - AGC is what drives the S-Meter. AGC is only an issue if you want to derive signal strength via modulation levels - which nobody here does anyway. My understanding of why the shielded loop performs this way is that near field noise is cancelled while far field signal is only attenuated by some factor relating to capture area. In my temporary rooftop mount I was unable to easily check out the effect of broadside null. Tom has posted in this thread very simple metrics to obtain just what constitutes near field. The incantation of near/far fields belies simpler explanations. If there is any issue of noise that relates to its nearness, it follows that you are the source. You being the source means that you also have the capacity to correct (and building a magic antenna is possibly the most superstitious response to that problem). The loop simply has less coupling (and less signal - that means there is a constant of proportionality in S/N) than a full sized dipole sitting over this noisy domicile. I have a random wire antenna that passes within 2 feet of an 80W Fluorescent fixture with a humming ballast. I barely pull in S-1 worth of noise and a loop would stand to do worse at that same distance. If I find that little noise troublesome, I turn off the noise. The fact that the shielded loop performs as a dipole is proof of its efficient construction (many fail to achieve even this). There is very little more that can be said about its qualities short of its loss of sensitivity. 73's Richard Clark, KB7QHC |
Tdonaly wrote:
Cecil wrote, Beams seem to "know" how to receive a signal from one direction while ignoring noise from the opposite direction. My horizontal dipole seems to "know" how to ignore vertically polarized noise. Yes, but does your small, inefficient, shielded loop improve the signal-to-noise ratio in the directions of its maximum gain over say, a non shielded loop? Depends upon the source of the noise. I remember a small shielded loop being effective against localized electrical noise in my college dorm. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Depends upon the source of the noise. I remember a small shielded loop
being effective against localized electrical noise in my college dorm. -- 73, Cecil http://www.qsl.net/w5dxp ======================================= Yes, but did it make any difference when you removed the shielding? |
Tdonaly wrote:
Yes, but does your small, inefficient, shielded loop improve the signal-to-noise ratio in the directions of its maximum gain over say, a non shielded loop? Many claim this, but I didn't see it when I compared them. I found a shielded coax loop just as susceptible to local, and not so local noise, as a non shielded loop assuming both are balanced. This is not counting the feedline, or any common mode currents unbalancing the loops. Both are capable of very sharp nulls. No difference really, and both are good at nulling a noise source. But a shielded coax loop quieter than a regular loop? I don't see it. It's not the loop itself, or having a shield. It's the keeping of good balance. The shielded loop design and method of feeding forces a good balance. But if you have a regular loop that is also just as balanced, I maintain it's just as "quiet". To me, this "shielded loop being quieter" theory is an old wives tail of sorts. My two favorite MW loops are both unshielded. Ones a 16 inch dia circle with 12 turns, and my big one is a diamond with 44 inches per side. "5 turns". Both are on floor stands indoors, and rotate. I've tried using shielded coax loops, and I saw no reduction of noise. I've also compared using both shielded and non shielded coupling loops to feed the loops. Again, no difference in noise levels. MK -- http://web.wt.net/~nm5k |
Mark Keith wrote,
Tdonaly wrote: Yes, but does your small, inefficient, shielded loop improve the signal-to-noise ratio in the directions of its maximum gain over say, a non shielded loop? Many claim this, but I didn't see it when I compared them. I found a shielded coax loop just as susceptible to local, and not so local noise, as a non shielded loop assuming both are balanced. This is not counting the feedline, or any common mode currents unbalancing the loops. Both are capable of very sharp nulls. No difference really, and both are good at nulling a noise source. But a shielded coax loop quieter than a regular loop? I don't see it. It's not the loop itself, or having a shield. It's the keeping of good balance. The shielded loop design and method of feeding forces a good balance. But if you have a regular loop that is also just as balanced, I maintain it's just as "quiet". To me, this "shielded loop being quieter" theory is an old wives tail of sorts. My two favorite MW loops are both unshielded. Ones a 16 inch dia circle with 12 turns, and my big one is a diamond with 44 inches per side. "5 turns". Both are on floor stands indoors, and rotate. I've tried using shielded coax loops, and I saw no reduction of noise. I've also compared using both shielded and non shielded coupling loops to feed the loops. Again, no difference in noise levels. MK -- http://web.wt.net/~nm5k This pretty much squares with an article on shielded loops written by Glenn S. Smith of the Georgia Institue of Technology in _The Antenna Engineering Handbook_. He says the shield enforces symmetry so that the pattern doesn't suffer, and that's what it's supposed to do. No mention of noise at all. 73, Tom Donaly, KA6RUH |
Mark, I fully agree.
The amount of unscreened signal picked up by an unscreened multi-turn loop is negligible compared with what is picked up by the action of the loop itself and then magnified by the Q of the loop. The unwanted signal cannot possibly be more than that which would be picked up by a very short vertical of height equal to the loop diameter and would probably be less. If there's a problem it is more likely to be picked up on the feedline which is not influenced by the presence or absence of a screen around the loop. If something must be screened then screen the feedline. Loop screening is needed only when precision direction-finding bearings are being taken with an in-the-clear, precision-constructed, large loop. ---- Reg, G4FGQ |
"Tdonaly" wrote in message ... Mark Keith wrote, Tdonaly wrote: Yes, but does your small, inefficient, shielded loop improve the signal-to-noise ratio in the directions of its maximum gain over say, a non shielded loop? Many claim this, but I didn't see it when I compared them. I found a shielded coax loop just as susceptible to local, and not so local noise, as a non shielded loop assuming both are balanced. This is not counting the feedline, or any common mode currents unbalancing the loops. Both are capable of very sharp nulls. No difference really, and both are good at nulling a noise source. But a shielded coax loop quieter than a regular loop? I don't see it. It's not the loop itself, or having a shield. It's the keeping of good balance. The shielded loop design and method of feeding forces a good balance. But if you have a regular loop that is also just as balanced, I maintain it's just as "quiet". To me, this "shielded loop being quieter" theory is an old wives tail of sorts. My two favorite MW loops are both unshielded. Ones a 16 inch dia circle with 12 turns, and my big one is a diamond with 44 inches per side. "5 turns". Both are on floor stands indoors, and rotate. I've tried using shielded coax loops, and I saw no reduction of noise. I've also compared using both shielded and non shielded coupling loops to feed the loops. Again, no difference in noise levels. MK -- http://web.wt.net/~nm5k This pretty much squares with an article on shielded loops written by Glenn S. Smith of the Georgia Institue of Technology in _The Antenna Engineering Handbook_. He says the shield enforces symmetry so that the pattern doesn't suffer, and that's what it's supposed to do. No mention of noise at all. 73, Tom Donaly, KA6RUH That's what the ARRL antenna book also claims. They talk about shielded loops in the context of direction finding antennas. The shield is supposed to make the antenna balanced with respect to ground, and retain directionality. Also, and I don't recall if anybody mentioned this, but the shield can not be closed around the circumference, and the maximum wire length is on the order of lambda/10. The loop is tuned to resonance with a parallel capacitor. Tam/WB2TT |
Reg Edwards wrote:
If there's a problem it is more likely to be picked up on the feedline which is not influenced by the presence or absence of a screen around the loop. Agreed If something must be screened then screen the feedline. It generally is screened already (coax) but it does need some kind of balun. It's amazing how many loop designs are paranoid about balancing and screening the loop itself, but then connect the coax in a totally unbalanced way. The result is a beautifully balanced loop in parallel with a vertically polarized random wire. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Hi Ian,
Some old wives even extoll the virtues of screening the coupling loop of a magloop. It may be kindly said that screening a loop at least does no harm. But the screen greatly increases capacitance across the loop and thereby restricts the tuning range of the proper capacitor. The number of turns has to be decreased. Or in the case of a single-turn loop its diameter must be reduced which also rapidly reduces receiving sensitivity. I've a feeling it also degrades loop Q. It certainly can't improve it. ---- Reg, G4FGQ ======================================== "Ian White, G3SEK" wrote in message ... Reg Edwards wrote: If there's a problem it is more likely to be picked up on the feedline which is not influenced by the presence or absence of a screen around the loop. Agreed If something must be screened then screen the feedline. It generally is screened already (coax) but it does need some kind of balun. It's amazing how many loop designs are paranoid about balancing and screening the loop itself, but then connect the coax in a totally unbalanced way. The result is a beautifully balanced loop in parallel with a vertically polarized random wire. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
"William Mutch" schreef in bericht the shielded loop performs this way is that near field noise is cancelled while far field signal is only attenuated by some factor relating to capture area. In my temporary rooftop mount I was unable to easily check out the effect of broadside null. William, I have done some work on local QRM reduction during the last few years. Summarized on: http://home.plex.nl/~jmsi/ Most important is avoiding any coupling with the coax/feedline. With small magnetic loops this is easy to accomplish and my guess is that this is why loops are less susceptible for local QRM. That is why I choose small loops instead of small dipoles. 73 de Jan PA0SIM |
Reg Edwards wrote:
Depends upon the source of the noise. I remember a small shielded loop being effective against localized electrical noise in my college dorm. Yes, but did it make any difference when you removed the shielding? All I know is that it was extremely superior to a 5' telescoping vertical receiving antenna. I was amazed and delighted at the difference. I could copy Radio Moscow on my SX-99 which I couldn't even detect on the 5' vertical. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Reg Edwards wrote:
"Yes, but did it make any difference when you removed the shielding?" I think Mark Keith`s testimony is accurate. Signal grabbing depends on the area enclosed by the loop. Small loops discriminate against noise due to their directional response. So, if the actual antenna is the shield or the contained conductor makes little difference except we have Terman`s testimony that the shield can equalize electrostatic response and in some cases reduce noise. Best regards, Richard Harrison, KB5WZI |
On Tue, 13 Jul 2004 17:57:21 -0500, "Crazy George"
wrote: OH, for Pete's sake. Loops are sensitive to the H vector. Wires receive the E vector. Most near field noise tends to be predominantly E field. But, that seems to only be effective up to 3 or 4 MHz, due to the wavelength factor, i. e. the near field shrinks as you go higher in frequency. Fully formed far field wavefronts of noise sources will be just like wanted signals, and unless some polarization difference is available, then directivity is the only way to improve S/N. Only in special circumstances can you see much improvement above 5 MHz due to near field/far field differentiation. In the _far_ field both the E and H fields are inversely proportional to distance and have the 120 pi (377 ohm) relation (impedance) between the fields. However, in the _near_field_ ( 1 lambda) the 377 ohm relationship is no longer valid and the magnetic field is inversely proportional to the square of the distance, while the electric field is inversely proportional to the cube of distance. Summarising the graph from an article by Lloyd Butler VK5BR in Amateur Radio, August 1990: The output voltages from both E and H field antenna system are calibrated to the same value at 1 lambda (i.e. in the far field). The antennas are moved closer, when the E and H antennas are moved to 0.05 lambda, the E antenna delivers 50 dB and the H antenna 40 dB (relative to 1 lambda) i.e. the H-field is 10 dB quieter. At 0.005 lambda, the E field antenna output is 110 dB and the H-field 80 dB, i.e. the H field antenna is 30 dB is quieter. Thus, with same far field sensitivity, the sensitivity to very local interference is attenuated considerably when _only_ the H field is used. However, at 3.5 MHz and 80 m wavelength, 0.05 lambda corresponds to 4 m and 0.005 lambda to 40 cm, so we are talking about really close noise sources. At even higher frequencies the number of potential interference sources is dropping within the 0.05 (or even 0.1) lambda radius from the receiving antenna, in which the H antenna has an advantage. However, on the 135 kHz LF band (lambda 2.2 km), the distances would be 110 m resp. 11 m, thus much more unwanted interface sources could be eliminated. Shielding the H-loop simply prevents the stronger E field from entering the loop and thus destroying part of the advantage of using the H-antenna. Paul OH3LWR |
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