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#11
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H FIELD ANTENNAS?
Justin Gill wrote:
"Is anyone aware of any source of information / theory on H Field antennas, such as Chelton Loop for HF?' Search on H-field antenna. Then click on "Standard H-field NRSC antenna -Chris Scott and Associates. The LP-S series stanard H-field Antenna is specifically designed for emission measurement of AM broadcast stations using a spectrum analyzer or other calibrated receiver. Best regards, Richard Harrison, KB5WZI |
#12
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H FIELD ANTENNAS?
Roy Lewallen wrote:
Bill Ogden wrote: OK, let me display my ignorance once again. There are many construction articles about ferrite-core antennas for the low bands. (Not to mention all the ferrite-core antennas in AM receivers.) Are these not H-field antennas, to a large extent? Only very locally, and only to a limited extent. When a signal originates far from an antenna, the response to E and H fields is in the ratio of about 377 ohms, the impedance of free space. This is true for *all antennas*. In other words, all antennas have the same relative E and H response to signals originating far away. Very close to a small loop antenna, response is greater to an H field than E field. It does respond to both, however, as all antennas must. As you get farther away from the antenna, the response to the H field decreases in relation to the E field response. At around an eighth wavelength distance from the antenna, the response to E and H fields are about the same as for a distant source. Beyond about an eighth wavelength, the response to the H field is actually *less* than the response to an E field compared to a source at a great distance. The ratio of E to H field responses then decreases to the distant value as you get farther from the antenna. In summary, the antenna responds more strongly to the H field if the source is within about an eighth of a wavelength from the antenna. Beyond that, it actually responds more strongly to the E field relative to the H field than a short dipole or many other antennas -- you could more properly call it an "E-field antenna" in its response to signals beyond about an eighth wavelength. The difference in relative E and H field response among all antennas becomes negligible at great distances; for antennas which are small in terms of wavelength, the difference becomes negligible beyond about a wavelength. Now, suppose you could make a magic antenna which would respond only to the H field of a signal originating at any distance from the antenna (which is impossible). What advantage would it have over a real antenna? Remember that the E/H ratio of any signal originating very far away is 377 ohms, regardless of what kind of antenna or source it came from. Roy Lewallen, W7EL There seems to be a number of commercial antennas described as H-field antennas intended for LORAN application. Most claim improved immunity to precipitation static. Is there a theoretical basis for such claims? Thanks. Chuck ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
#13
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H FIELD ANTENNAS?
There seems to be a number of commercial antennas
described as H-field antennas intended for LORAN application. Most claim improved immunity to precipitation static. Is there a theoretical basis for such claims? Yes. It increases sales just like zoom zoom zoom in car advertisements. Seriously, precipitation static is caused by corna discharge from an antenna or object someplace near the antenna. The radiated field from that leakage current can be almost any field impedance and will always be a mixture of time-varying electric and magnetic fields. What a small loop actually buys you is a compact antenna that has no sharp protruding edges, and that decreases the chances of having corona right from the antenna. A whip would have a sharp protruding point, and that would encourge corona discharge and the resulting noise we call "precipitation static". Other than that, there is no advantage. 73 Tom |
#14
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H FIELD ANTENNAS?
Search on H-field antenna. Then click on "Standard H-field NRSC antenna -Chris Scott and Associates. The LP-S series stanard H-field Antenna is specifically designed for emission measurement of AM broadcast stations using a spectrum analyzer or other calibrated receiver. ========================================= Is this just the usual pseudo-scientific language used by American antenna salesmen and others? It all helps to boost sales to the gullible public. |
#15
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H FIELD ANTENNAS?
Reg Edwards wrote:
Is this just the usual pseudo-scientific language used by American antenna salesmen and others? Yes. American antenna salesmen haven't yet gotten as sophisticated as the British inventors and purveyors of the CFA. But they're learning. Be patient -- perhaps someday they'll reach that level. It all helps to boost sales to the gullible public. Indeed. Roy Lewallen, W7EL |
#17
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H FIELD ANTENNAS?
On Tue, 06 Jun 2006 20:49:54 -0400, chuck wrote:
I think the precipitation static talked about is caused by the accumulation on the antenna of charges carried by precipitation particles (e.g., snow). Hi Chuck, Snow, rain, dust, soot, anything airborne which in fact is the principle carrier of current from earth to air in the current cycle that feeds the electrostatic potential of lightning clouds (which amounts to about 600 V/m). wouldn't the charge on the antenna simply redistribute itself over the body of the aircraft (assuming it is metal) and not accumulate on the antenna as it would were the antenna insulated from the aircraft body? Charge moves to the smallest radius surface, and once there, if there is sufficient flux will break down insulators (air being one) and arc-over (corona discharge). One solution is to reduce the number of small radius surfaces (pin-points) and loops qualify (vastly larger radius than a monopole tip). However, and at altitude, if the loop is in fact a square, then the corners are prone to discharge. HCJB antenna design tested this at altitude in Quito, Ecuador and they solved it by moving the feed point so that the high potential fell in mid-span, instead of at the corners. Auto manufacturers also had to contend with the problem, they put small round caps on the ends of their car antennas. 73's Richard Clark, KB7QHC |
#18
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H FIELD ANTENNAS?
"Roy Lewallen" wrote Very close to a small loop antenna, response is greater to an H field than E field. It does respond to both, however, as all antennas must. As you get farther away from the antenna, the response to the H field decreases in relation to the E field response. At around an eighth wavelength distance from the antenna, the response to E and H fields are about the same as for a distant source. Beyond about an eighth wavelength, the response to the H field is actually *less* than the response to an E field compared to a source at a great distance. The ratio of E to H field responses then decreases to the distant value as you get farther from the antenna. In summary, the antenna responds more strongly to the H field if the source is within about an eighth of a wavelength from the antenna. Beyond that, it actually responds more strongly to the E field relative to the H field than a short dipole or many other antennas -- you could more properly call it an "E-field antenna" in its response to signals beyond about an eighth wavelength. The difference in relative E and H field response among all antennas becomes negligible at great distances; for antennas which are small in terms of wavelength, the difference becomes negligible beyond about a wavelength. But according to W8JI "teachings" there is no way that electrostatic shield on a small loop antenna would work as a shield, attenuating E field dominant signals or noise generated within that 1/8 or about wavelength. According to him, it works as an antenna. Some scientwists can not comprehend that electrostatic shield shunts the predominantly E field generated in the vicinity. It is the FACT, easily observable by anyone building shielded small loop and having TV birdies, PS bricks or arcing noise source within about 1/8 of a wavelength. W8JI wrote: Seriously, precipitation static is caused by corna discharge from an antenna or object someplace near the antenna. The radiated field from that leakage current can be almost any field impedance and will always be a mixture of time-varying electric and magnetic fields. Roy, 'splain to him about this 1/8 or so thing. He still dungetit. 73 Yuri, K3BU |
#19
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H FIELD ANTENNAS?
Yuri Blanarovich wrote:
. . . Roy, 'splain to him about this 1/8 or so thing. He still dungetit. Tom understands it, but I see you don't quite have a handle on it yet. Roy Lewallen, W7EL |
#20
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H FIELD ANTENNAS?
Precipitation static, eg., from highly charged raindrops and fine snow
or fine sand, impinging on the antenna wire, just causes an increase in receiver white noise level. It can be reduced but not removed by using a very thickly insulated antenna wire, like the inner conductor of a coaxial cable complete with its polyethylene jacket. ---- Reg. |
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