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H FIELD ANTENNAS?
Is anyone aware of any sources of information/theory on H Field
antennas, such as the Chelton Loop for HF? |
H FIELD ANTENNAS?
Any theory that predicts any antenna can produce an H field without an E
field, or that the H field is unusually large beyond a fraction of a wavelength from an antenna(*), is flawed. So you're free to make up any theory you like, and it'll be just as accurate. (*) Or, from a receiving standpoint, that an antenna responds only to an H field or it responds more strongly to an H field beyond a fraction of a wavelength from the antenna. Roy Lewallen, W7EL wrote: Is anyone aware of any sources of information/theory on H Field antennas, such as the Chelton Loop for HF? |
H FIELD ANTENNAS?
In article , Roy Lewallen wrote: Any theory that predicts any antenna can produce an H field without an E field, or that the H field is unusually large beyond a fraction of a wavelength from an antenna(*), is flawed. So you're free to make up any theory you like, and it'll be just as accurate. (*) Or, from a receiving standpoint, that an antenna responds only to an H field or it responds more strongly to an H field beyond a fraction of a wavelength from the antenna. Upon a cursory search, it appears to me that "H-field antenna" is probably another (perhaps misleading) term for "small shielded receiving loop". Discussions about the latter do seem to have the requisite amount of lore, mythology, and strenuous disagreements as to just what this sort of antenna does respond to and how it works. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
H FIELD ANTENNAS?
Are you trying to pull our leg? A google search for "Chelton Loop"
antenna turns up only references to a street, Chelton Loop, in Colorado Springs. If there's a "Chelton Loop" antenna, it must not have had much written about it. If you want to detect magnetic fields at HF, a small coil of wire should work well. The size would depend on the size of the magnetic field you're probing, and the spatial accuracy you want. If you want to receive electromagnetic signals, as others have posted, be careful about claims of sensing "only" the H field. Cheers, Tom wrote: Is anyone aware of any sources of information/theory on H Field antennas, such as the Chelton Loop for HF? |
H FIELD ANTENNAS?
K7ITM wrote:
Are you trying to pull our leg? A google search for "Chelton Loop" antenna turns up only references to a street, Chelton Loop, in Colorado Springs. If there's a "Chelton Loop" antenna, it must not have had much written about it. If you want to detect magnetic fields at HF, a small coil of wire should work well. The size would depend on the size of the magnetic field you're probing, and the spatial accuracy you want. If you want to receive electromagnetic signals, as others have posted, be careful about claims of sensing "only" the H field. Cheers, Tom wrote: Is anyone aware of any sources of information/theory on H Field antennas, such as the Chelton Loop for HF? FWIW, Tom, "chelton" was probably a typo. There is indeed a Chilton Loop Antenna at a research facility in the UK. I think the name refers to the loop used at the Chilton facility, rather than to a particular antenna design. Chuck http://www.ukssdc.ac.uk/ionosondes/chiltonpiccys.html Pictures from the Chilton site ----== 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 =---- |
H FIELD ANTENNAS?
chuck wrote:
FWIW, Tom, "chelton" was probably a typo. There is indeed a Chilton Loop Antenna at a research facility in the UK. I think the name refers to the loop used at the Chilton facility, rather than to a particular antenna design. There seem to be two possible kinds of "Chilton loop". One is at www.chilton.com, which is a web-controlled SW radio receiver located in the USA. This is just a loop of wire in some guy's attic. The second kind may be related to the ionosondes located at the Rutherford Appleton Lab, Chilton, UK; and at Port Stanley, Falkland Islands. These do use crossed loop antennas (as the referenced picture shows)... but in 25 years living just a few miles down the road, including 12 years of working right next to RAL and regularly eating lunch with the hams who work there, I never heard or saw the term "Chilton loop" until yesterday, right here. However, I will make some specific inquiries about those loops. Now if you want something really serious to talk about, those RAL/Stanley ionosondes are being closed down! The scientists who work there are horrified, because it would pull the plug on a major international source of daily data, and terminate the world's longest-running continuous sequence of ionospheric observations: http://www.wdc.rl.ac.uk/wdcc1/news/closure_notice.html (This actually looks like a clumsy political move to shift the running costs away from the UK science budget and find some other source of funding, using the threat of closure as a way to get attention. But suicide bids of this kind can occasionally go wrong...) -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
H FIELD ANTENNAS?
"Ian White GM3SEK" wrote in message ... chuck wrote: FWIW, Tom, "chelton" was probably a typo. There is indeed a Chilton Loop Antenna at a research facility in the UK. I think the name refers to the loop used at the Chilton facility, rather than to a particular antenna design. There seem to be two possible kinds of "Chilton loop". One is at www.chilton.com, which is a web-controlled SW radio receiver located in the USA. This is just a loop of wire in some guy's attic. The second kind may be related to the ionosondes located at the Rutherford Appleton Lab, Chilton, UK; and at Port Stanley, Falkland Islands. These do use crossed loop antennas (as the referenced picture shows)... but in 25 years living just a few miles down the road, including 12 years of working right next to RAL and regularly eating lunch with the hams who work there, I never heard or saw the term "Chilton loop" until yesterday, right here. However, I will make some specific inquiries about those loops. Now if you want something really serious to talk about, those RAL/Stanley ionosondes are being closed down! The scientists who work there are horrified, because it would pull the plug on a major international source of daily data, and terminate the world's longest-running continuous sequence of ionospheric observations: http://www.wdc.rl.ac.uk/wdcc1/news/closure_notice.html (This actually looks like a clumsy political move to shift the running costs away from the UK science budget and find some other source of funding, using the threat of closure as a way to get attention. But suicide bids of this kind can occasionally go wrong...) -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek There is a company named Chelton that makes antennas listed on the web. Shows reference to a lot of military stuff. If they are claiming they have an H antenna then............... |
H FIELD ANTENNAS?
yes
|
H FIELD ANTENNAS?
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? Bill W2WO |
H FIELD ANTENNAS?
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 |
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 |
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 =---- |
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 |
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. |
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 |
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 |
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 |
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 |
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. |
H FIELD ANTENNAS?
The only useful purpose served by making a loop antenna from coaxial
cable is to ensure capacitance balance of the loop against ground, so sharpening its directional nulls and, incidentally of course, to support the very thin inner conductor which would otherwise collapse under its own weight. The outer coaxial conductor has no effect on signal to noise ratio as perceived by the receiver. S/N ratio depends only on what's contained in the local field itself. If there's any difference in S/N ratio due to use of a tuned loop, as with a magloop, then it is due to the loop's very narrow bandwidth - not the shield. ---- Reg. |
H FIELD ANTENNAS?
Reg Edwards wrote: 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. I've never seen a case of precitation static occuring that way. In every single case I've seen, whether on tall buildings, tall towers, or antenna hear earth, it has always been corona discharges from the antenna or objects near the antenna. How do I know this? 1.) I had side by side "insulated" and "unisulated" Beverage antenna wires that are otherwide identical except for being spaced a few dozen feet apart, and the antebnna pointed towards my tall towers had precip static and the others did not. Both were equal in noise despite the fact they are hit by the same rain or dust. 2.) I have Yagis on towers that are identical, and the LOWER antenna almost never has precipitation static despite the fact they are hit by the same rain or dust. 3.) I've had dipoles at various heights, and the lower dipole always has much less precipitation staic than the high dipole despite the fact they get the same rain or dust. 4.) The period of the noise has nothing at all to do with the number of droplets hitting the antenna. It increases in pitch as the charge gradient between earth and clouds builds, then when lightning flashes it immediatly stops without time delay. 5.) On tall buildings on dark nights in storms, we could actually hear the same pitch noise as the repeaters rebroadcast, and walk to the noise source and actually see the corona. 6.) Antennas in fiberglass radomes were no quieter than bare metal dipoles on tall buildings. 7.) I even used an electrostatic sprayer to charge droplets and hit an antenna, and could only simulate noise when the antenna element had a sharp point and I got near the sharp point...at which time I could see faint corona. 73 Tom |
H FIELD ANTENNAS?
In article , Roy Lewallen
wrote: 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. The CFA proponents weren't sophisticated at all. The "inventors" probably read half of chapter one of an undergraduate electromagnetics textbook but forgot to read/understand the rest. Another source of embarrassment was that one of the CFA backers was a university EE professor. Go figure. Extraordinary claims but no extraordinary proof. BTW, in case you're interested, the British/Egyptian inventors' U.S. patent number is 5155495. It's patented so it must work... 73s from N4GGO, John Wood (Code 5550) e-mail: Naval Research Laboratory 4555 Overlook Avenue, SW Washington, DC 20375-5337 |
H FIELD ANTENNAS?
Dear Tom:
Your message may one of the most interesting and unexpected that I have read in a long time. Some comments follow. Please note my extreme reluctance to engage in anything but a calm exchange of experiences and opinions. I have no interest in provoking you. Your experience does not seem to agree with experience at remote, flat, treeless sites here in Michigan. Please note the qualifiers in the last sentence. Especially in the UP of Michigan, at certain times of the year, P-noise is the major factor in limiting radio use. P-noise is not found on an antenna imbedded in a clump of trees when an antenna out in the open (many wavelengths from the first antenna) has P-noise. The follow-on is that since most sites are urban or suburban, few radio amateurs will experience P-noise. P-noise is observed when there is no rain nor thunderstorms, but plenty of wind. This is suggestive of moving charge discharging into the antenna. Of course, one could define this action as being "corona." Of course, if one places enough charge on a piece of metal eventually there will be "corona." Many antennas have a conductive path to earth that makes such an accumulation of charge unlikely. There is no doubt that an antenna experiencing P-noise will radiate and thus noise will be received by nearby antennas. That is why successful receiving antennas here in the flatland are placed a long distance from metallic objects. Most people have never heard P-noise because their site precludes same. A paper published in August about 1961 (IEEE Vehicular Transactions) is one of the few references that has been published that deals with means for reducing P-noise. The article involved a fixed, not mobile, antenna. It appears that additional work has not been published that deals significantly with fixed antennas. (Lots of papers exist dealing with aircraft antennas.) Your #6 is interesting. Unfortunately, there is so much radiation from what else is on a tall building that it is difficult to sort out where excess noise is coming from. An antenna inside of a slightly conductive radome that is placed a long distance from anything that could radiate might be different. Your #7 is especially interesting. Our EMC group has on the drawing board just such experimentation. We will be on the lookout for "end effects." Your note is a valuable observation. Regards, Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: wrote in message ups.com... Reg Edwards wrote: 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. I've never seen a case of precitation static occuring that way. In every single case I've seen, whether on tall buildings, tall towers, or antenna hear earth, it has always been corona discharges from the antenna or objects near the antenna. How do I know this? 1.) I had side by side "insulated" and "unisulated" Beverage antenna wires that are otherwide identical except for being spaced a few dozen feet apart, and the antebnna pointed towards my tall towers had precip static and the others did not. Both were equal in noise despite the fact they are hit by the same rain or dust. 2.) I have Yagis on towers that are identical, and the LOWER antenna almost never has precipitation static despite the fact they are hit by the same rain or dust. 3.) I've had dipoles at various heights, and the lower dipole always has much less precipitation staic than the high dipole despite the fact they get the same rain or dust. 4.) The period of the noise has nothing at all to do with the number of droplets hitting the antenna. It increases in pitch as the charge gradient between earth and clouds builds, then when lightning flashes it immediatly stops without time delay. 5.) On tall buildings on dark nights in storms, we could actually hear the same pitch noise as the repeaters rebroadcast, and walk to the noise source and actually see the corona. 6.) Antennas in fiberglass radomes were no quieter than bare metal dipoles on tall buildings. 7.) I even used an electrostatic sprayer to charge droplets and hit an antenna, and could only simulate noise when the antenna element had a sharp point and I got near the sharp point...at which time I could see faint corona. 73 Tom |
H FIELD ANTENNAS?
wrote in message ups.com... Reg Edwards wrote: 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. I've never seen a case of precitation static occuring that way. In every single case I've seen, whether on tall buildings, tall towers, or antenna hear earth, it has always been corona discharges from the antenna or objects near the antenna. How do I know this? 1.) I had side by side "insulated" and "unisulated" Beverage antenna wires that are otherwide identical except for being spaced a few dozen feet apart, and the antebnna pointed towards my tall towers had precip static and the others did not. Both were equal in noise despite the fact they are hit by the same rain or dust. 2.) I have Yagis on towers that are identical, and the LOWER antenna almost never has precipitation static despite the fact they are hit by the same rain or dust. 3.) I've had dipoles at various heights, and the lower dipole always has much less precipitation staic than the high dipole despite the fact they get the same rain or dust. 4.) The period of the noise has nothing at all to do with the number of droplets hitting the antenna. It increases in pitch as the charge gradient between earth and clouds builds, then when lightning flashes it immediatly stops without time delay. 5.) On tall buildings on dark nights in storms, we could actually hear the same pitch noise as the repeaters rebroadcast, and walk to the noise source and actually see the corona. 6.) Antennas in fiberglass radomes were no quieter than bare metal dipoles on tall buildings. 7.) I even used an electrostatic sprayer to charge droplets and hit an antenna, and could only simulate noise when the antenna element had a sharp point and I got near the sharp point...at which time I could see faint corona. ======================================== Tom, The description "precipitate" clearly applies to what is being precipitated onto the antenna, eg., rain drops, hail-stones, snow particles, sand particles in a sandstorm, etc. When charged to a high potential, on impinging on the antenna wire, the charge on a particle is suddenly released causing a click in the headphones. A very rapid succession of small random clicks constitutes white noise. I, and everybody else in the uK, have experienced rain static dozens of times, sometimes 10 or 20 dB above S9 on the S-meter. At the start of a rain storm and when nearing its end, individual clicks can be heard. As expected, when the clouds are most highly charged, the noise is most intense when there is thunder about. It can amount to a roar. It is loudest on the lower HF bands and at MF but that may be due to the physically larger antennas. What you have been suffering from is not precipitation or rain static. You should give it a different name. If you have never experienced rain static, perhaps you disconnect your antenna when a thunder storm storm is approaching and before it starts to rain. ---- Reg. |
H FIELD ANTENNAS?
wrote:
Reg Edwards wrote: 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. I've never seen a case of precitation static occuring that way. I experienced that kind of static in Arizona with wind, extremely low humidity, and bare wire. I've never experienced it in East Texas. -- 73, Cecil http://www.qsl.net/w5dxp |
H FIELD ANTENNAS?
"Roy Lewallen" wrote in message ... 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 So I "don't get it" because I (and others) see the difference in reality, when electrostatic shield suppresses the local interference. You explain behavior of E and H field in the vicinity of antenna but that does not apply to "W8JI shield is the antenna" and "current at both ends of the loading coil is always the same". I will stick to my reality handle, rather than joining scientwist's chorus. 73 Yuri, K3BU |
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). "A system for determining the modulation imposed on a curl-free magnetic vector potential field.": http://jnaudin.free.fr/html/tepvppl.htm Other 'magic' antennae: http://rugth30.phys.rug.nl/quantummechanics/ab.htm Robust OP AMP Realization Of Chua's Circuit: http://citeseer.ist.psu.edu/kennedy92robust.html What advantage would it have over a real antenna? I read the main reason was less electrostatic interference but with less immunity to strong nearby stations. Does the magnetic field really have less noise than the E-field? Polarization is also an interesting component. 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. I seem to recall this had something to do with the speed of light not being infinite. Roy Lewallen, W7EL |
H FIELD ANTENNAS?
Cecil Moore wrote:
wrote: Reg Edwards wrote: 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. I've never seen a case of precitation static occuring that way. I experienced that kind of static in Arizona with wind, extremely low humidity, and bare wire. I've never experienced it in East Texas. Isn't this the triboelectric effect? I read this was a big problem for certain newer wireless applications. Energized TV antennas always feel 'gritty' when I brush my fingers lightly across them. Why is that? I also get a very mild shock sometimes, but that gritty electric sandpaper friction is very strange. Also the indoor TV antenna collects dust and vaporized cooking oil like there's no tomorrow. Is this like a Tesla coil? -- 73, Cecil http://www.qsl.net/w5dxp |
H FIELD ANTENNAS?
Bill Ogden wrote:
To return to the ferrite rod antenna: Ignoring the directional null capability (which might be very useful in some real-world circumstances) is there any advantage to a small ferrite rod antenna over a short wire antenna? For the 1980's CA 75m mobile antenna shootouts, a ferrite rod antenna was used for receiving because the local human bodies had much less of an effect upon it than, for instance, upon a hamstick antenna. I always assumed it was because a human body has more of an effect on the E-field than it does on the H-field. -- 73, Cecil http://www.qsl.net/w5dxp |
H FIELD ANTENNAS?
I understand that E and H fields are intrinsic parts of the same thing (for
radio waves, etc), and I am not trying to separate them along the lines discussed by some list participants. I would think that the E and H ratio of 377 is a function of the SI units of measurement involved. It would seem that there is the same amount of energy (at different and selected instances) in the E and H waves, and different units of measurement could produce a ratio of 1:1 (or anything else, with appropriate units of measurement). To return to the ferrite rod antenna: Ignoring the directional null capability (which might be very useful in some real-world circumstances) is there any advantage to a small ferrite rod antenna over a short wire antenna (assuming perfect amplifiers, as needed, following the antennas and assuming 160m or 80m usage)? As mentioned earlier, there have been a number of construction articles over the years explaining how a ferrite rod antenna did wonderful things for 160/80 operation. I have wondered if these results are generally valid, or were the result of the authors' pride in their works, or happened because the directional null abilities solved a local problem. Bill - W2WO |
H FIELD ANTENNAS?
My reality, and Tom's, fits with the clear explanations in Johnson's
_Antenna Engineering Handbook_ (successor to Jasik); King and Harrison's _Antennas and Waves_; King, Mimno, and Wing's _Transmission Lines, Antennas, and Wave Guides_; and undoubtedly others, since it comes from basic electromagnetic principles. I explained the nature of the E and H fields from a small loop antenna. This is the sum of the fields from each part of the loop. It is not representative of the field in the small region between the wire and shield of a "shielded" loop, as you seem to be trying to infer. If you'd spend a fraction of the time studying that you spend desperately trying to find something wrong with anything Tom says, you'd have a much better understanding of how antennas work. Roy Lewallen, W7EL Yuri Blanarovich wrote: "Roy Lewallen" wrote in message ... 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 So I "don't get it" because I (and others) see the difference in reality, when electrostatic shield suppresses the local interference. You explain behavior of E and H field in the vicinity of antenna but that does not apply to "W8JI shield is the antenna" and "current at both ends of the loading coil is always the same". I will stick to my reality handle, rather than joining scientwist's chorus. 73 Yuri, K3BU |
H FIELD ANTENNAS?
Bill Ogden wrote:
I understand that E and H fields are intrinsic parts of the same thing (for radio waves, etc), and I am not trying to separate them along the lines discussed by some list participants. I would think that the E and H ratio of 377 is a function of the SI units of measurement involved. It would seem that there is the same amount of energy (at different and selected instances) in the E and H waves, and different units of measurement could produce a ratio of 1:1 (or anything else, with appropriate units of measurement). Yes, that's correct. What I tried to do in my explanation was to relate the E/H ratio near a small loop with that of free space. That makes the units of measure immaterial. To return to the ferrite rod antenna: Ignoring the directional null capability (which might be very useful in some real-world circumstances) is there any advantage to a small ferrite rod antenna over a short wire antenna (assuming perfect amplifiers, as needed, following the antennas and assuming 160m or 80m usage)? You get a greater effective aperture (aka "capture area", and directly related to "effective length") from the ferrite rod antenna for a given physical size. This results in a larger signal for a given impinging field strength. If you had perfect amplifiers, that would make no difference, but real amplifiers generate noise, so a larger signal results in a better signal/noise ratio when you're at the level where the amplifier noise dominates the system noise figure. But if the signal level is large enough so that atmospheric noise dominates, having a greater aperture doesn't present any advantage. As mentioned earlier, there have been a number of construction articles over the years explaining how a ferrite rod antenna did wonderful things for 160/80 operation. I have wondered if these results are generally valid, or were the result of the authors' pride in their works, or happened because the directional null abilities solved a local problem. Anecdotal reports of "wonderful things" should always be highly suspect, and placebo effect high on the list of possible causes. It might be easier to get a good null with a ferrite rod antenna than with a casually built antenna of some other kind, and that would be a big potential advantage. When considering the value of anecdotal reports, consider the widely reported benefits of various kinds of speaker cable, and the staggering amount of money that's being extracted from the believers. Roy Lewallen, W7EL |
H FIELD ANTENNAS?
J. B. Wood wrote:
. . . It's patented so it must work... Yeah, like U.S. patent 6,025,810, "Hyper-Light-Speed Antenna" (http://tinyurl.com/h546u). Roy Lewallen, W7EL |
H FIELD ANTENNAS?
"Roy Lewallen" wrote If you'd spend a fraction of the time studying that you spend desperately trying to find something wrong with anything Tom says, you'd have a much better understanding of how antennas work. Roy Lewallen, W7EL Congratulations Roy, you have nove graduated from "W8JI school of personal mud slinging" when running out of arguments. How perceptive: " ...desperately....anything Tom says...." "Better understanding" - you mean swallowing fallacies you scientwists proclaim? I will stick with my understanding of how antennas work and I can measure, vs. your misapplied theories why it "can't be so". 73 Yuri, K3BU |
H FIELD ANTENNAS?
J. Mc Laughlin wrote:
P-noise is not found on an antenna imbedded in a clump of trees when an antenna out in the open (many wavelengths from the first antenna) has P-noise. The follow-on is that since most sites are urban or suburban, few radio amateurs will experience P-noise. That does not disagree with anything I said. A lower antenna surrounded by taller objects is not subject to the same high voltage gradient as an antenna out in a flat clear field. P-noise is observed when there is no rain nor thunderstorms, but plenty of wind. This is suggestive of moving charge discharging into the antenna. So how does it get there? How does it build up? Where is the spark arc or sizzle? Of course, one could define this action as being "corona." Of course, if one places enough charge on a piece of metal eventually there will be "corona." Many antennas have a conductive path to earth that makes such an accumulation of charge unlikely. The fact is grounded or ungrounded antennas all behave the very same way. Ask anyone who has yagis on towers. It is a potential difference between earth and the atmosphere around the antenna. It isn't the antenna charging up so much differently than earth. It is the difference in potential between the antenna and the space around the antenna. Remember those old tall mast wooden sailing ships soaked with sal****er and the fire off the yardarms at night? Your #6 is interesting. Unfortunately, there is so much radiation from what else is on a tall building that it is difficult to sort out where excess noise is coming from. An antenna inside of a slightly conductive radome that is placed a long distance from anything that could radiate might be different. You can walk right up to the noise source, and even see the corona at night. It's very easy to take a FSM with audio monitor or AM receiver with S meter and walk the roof for strongest noise, and it will generally take you right to the tallest sharpest object (grounded or not) on the roof. The last place you want to be is the tallest antenna on the building. Get high winds or inclement weather and you will be destined for noise....grounded antenna or not. We serviced dozens of repeaters and a few STL or Remote links in the 70's, it was a pattern that repeated. I have a suggestion. Go to a forum where there are many people with antennas at various heights, like a contesting reflector. Ask people who have similar or identical antennas at various heights on a single tall tower what they observe during high winds, nasty weather, or rain. The very same wind and the very same moisture is impacting all of the antennas, but without fail they will tell you the lower antennas are always much better and the taller antennas are the first to go. If the P-staic is actually coming from the particles or moisture in air striking the antenna, and if the same basic sample of weather is at all the antennas, why are the upper antennas affected more? If it is the conductor charging, why do plumber's delight antennas or folded elements with grounded centers have the same noise as insulated elements? If it is moisture or particles striking the antenna causing the problem, why is an insulated antenna with a single sharp protrusion just as noisey as a bare antenna? Why doesn't the noise follow the pattern of the particle rate, and why does it occur (as you even seemed to say) when there is no actual precipitation? Since I've always had towers taller than 100 feet, and since I've worked on VHF and UHF systems that had to stay up during storms, I've spent a lot of time looking at this. I've not found anything that points to the antenna charging differently than earth or being struck by charged particles. 73 Tom |
H FIELD ANTENNAS?
wrote:
J. Mc Laughlin wrote: P-noise is observed when there is no rain nor thunderstorms, but plenty of wind. This is suggestive of moving charge discharging into the antenna. So how does it get there? How does it build up? Where is the spark arc or sizzle? This is a well known phenomenon in Arizona. What else, besides charged dust particles, could cause arcing at coax connectors on a perfectly clear windy day? -- 73, Cecil http://www.qsl.net/w5dxp |
H FIELD ANTENNAS?
Dear Tom:
It appears that two noise mechanisms exist. The two are P-noise and corona noise. A receiver will experience close to white noise in both cases. However, corona noise tends to be accompanied by sudden stops and starts and P-noise starts with a sequence of perceptibly time spaced pops that increase in rate. If there is corona off of the top of a structure then it is reasonable to expect the antennas most close to the corona will "hear" more noise than the antennas that are farther away (such as below). It is also to be expected that moving charged particles that are higher above the ground will carry more charge on the average than charged particles that are moving near the ground. Depending on the wind and gradient, I expect that there is a height below which few charged particles are found when higher above ground charged particles are common. In short: If one can see corona, it will be the dominate noise source. If the gradient with altitude is not sufficient for corona, and weather conditions are such that moving charged particles exist, then out in the open the higher antennas are expected to have more discharges from moving charged particles per second and more noise than experienced by lower antennas. I have offered an alternative explanation for why, absent corona, higher antennas might well experience more noise. Actual precipitation (rain, snow, hail) is not needed for P-noise. Moving dust particles can carry charge and become charged. The noise does follow the "pattern of the particle rate." However, as you understand from other work, when the rate becomes high enough compared to the bandwidth of the receiver the result is essentially indistinguishable from white noise. Even with a 400 Hz bandwidth, the onset of P-noise is unique and comprises a sequence of pops that either die away or increase in rate to produce prodigious amounts of noise. I have used a time blanking circuit - noise clipper - and find that it is effective at lower rates. Corona noise does not seem to have the same temporal characteristics. A moving charged particle is able to discharge into an insulated conductor with aplomb. It is the very-close-to-the-antenna sudden accelerations of charge that produce noise (radio waves). What has shown promise is the use of slightly conductive coverings. The theory is that the amplitude of the pop will be reduced because the rate of charge transfer will be slowed. UV resistant materials that are easy to apply and that are not expensive seem not to exist. Obviously, too much conductivity would be ineffective. Absent actual corona, a noise mechanism is contended that comprises the sudden transfer of some or all of the charge on a moving charged particle (that occurs naturally) into an antenna's structure, support or even into insulation around same. A near optimum, HF, DX, low-noise receiving antenna is a small, horizontal, unturned loop antenna with an amplifier that is mounted on a wood pole having no metal inserts. The pole is some 200 meters from any exposed metal. The coax that runs up the pole to the amplifier is encased in conductive, plastic conduit as is the loop's wire. This antenna has close to a null at the zenith and is omnidirectional in azimuth. It is contended that what I have observed is not in conflict with what you have observed with corona discharges. 73 Mac N8TT P.S. Some months ago you asked about V antennas for low HF or MF use involving a 300 foot tower. I found that an interesting topic and did some analysis, which I tried to sent to you. Unfortunately, the E-mail address did not work. My conclusion, was, as well as I am able to remember, the same as yours: at the low frequencies involved, the effort did not have a reasonable pay-back. -- J. Mc Laughlin; Michigan U.S.A. Home: wrote in message oups.com... J. Mc Laughlin wrote: P-noise is not found on an antenna imbedded in a clump of trees when an antenna out in the open (many wavelengths from the first antenna) has P-noise. The follow-on is that since most sites are urban or suburban, few radio amateurs will experience P-noise. That does not disagree with anything I said. A lower antenna surrounded by taller objects is not subject to the same high voltage gradient as an antenna out in a flat clear field. P-noise is observed when there is no rain nor thunderstorms, but plenty of wind. This is suggestive of moving charge discharging into the antenna. So how does it get there? How does it build up? Where is the spark arc or sizzle? Of course, one could define this action as being "corona." Of course, if one places enough charge on a piece of metal eventually there will be "corona." Many antennas have a conductive path to earth that makes such an accumulation of charge unlikely. The fact is grounded or ungrounded antennas all behave the very same way. Ask anyone who has yagis on towers. It is a potential difference between earth and the atmosphere around the antenna. It isn't the antenna charging up so much differently than earth. It is the difference in potential between the antenna and the space around the antenna. Remember those old tall mast wooden sailing ships soaked with sal****er and the fire off the yardarms at night? Your #6 is interesting. Unfortunately, there is so much radiation from what else is on a tall building that it is difficult to sort out where excess noise is coming from. An antenna inside of a slightly conductive radome that is placed a long distance from anything that could radiate might be different. You can walk right up to the noise source, and even see the corona at night. It's very easy to take a FSM with audio monitor or AM receiver with S meter and walk the roof for strongest noise, and it will generally take you right to the tallest sharpest object (grounded or not) on the roof. The last place you want to be is the tallest antenna on the building. Get high winds or inclement weather and you will be destined for noise....grounded antenna or not. We serviced dozens of repeaters and a few STL or Remote links in the 70's, it was a pattern that repeated. I have a suggestion. Go to a forum where there are many people with antennas at various heights, like a contesting reflector. Ask people who have similar or identical antennas at various heights on a single tall tower what they observe during high winds, nasty weather, or rain. The very same wind and the very same moisture is impacting all of the antennas, but without fail they will tell you the lower antennas are always much better and the taller antennas are the first to go. If the P-staic is actually coming from the particles or moisture in air striking the antenna, and if the same basic sample of weather is at all the antennas, why are the upper antennas affected more? If it is the conductor charging, why do plumber's delight antennas or folded elements with grounded centers have the same noise as insulated elements? If it is moisture or particles striking the antenna causing the problem, why is an insulated antenna with a single sharp protrusion just as noisey as a bare antenna? Why doesn't the noise follow the pattern of the particle rate, and why does it occur (as you even seemed to say) when there is no actual precipitation? Since I've always had towers taller than 100 feet, and since I've worked on VHF and UHF systems that had to stay up during storms, I've spent a lot of time looking at this. I've not found anything that points to the antenna charging differently than earth or being struck by charged particles. 73 Tom |
H FIELD ANTENNAS?
J. Mc Laughlin wrote:
It appears that two noise mechanisms exist. The two are P-noise and corona noise. A receiver will experience close to white noise in both cases. However, corona noise tends to be accompanied by sudden stops and starts and P-noise starts with a sequence of perceptibly time spaced pops that increase in rate. Pops are caused by something charging and flashing over. All it takes to eliminate pops is a leak resistance or a leak choke slow enough to keep the antenna from charging. I've never heard the slow popping noise called P-static by anyone I know, but that doesn't say some people don't call it that. I have dipole high in the air, and on a clear day with a fair breeze they will knock someone right on their butt if the feeder is unhooked and the antenna allowed to charge. It does that dust or no dust, although nasty weather seems to greatly increase charge rate. It's easy to see why that happens. http://www.who.int/peh-emf/publicati...d_Exposure.pdf There is a significant electric field as we increase height even in fair weather. Even though that is a very high impedance field, it doesn't take air movement to charge a high conductor that is well-insulated. I have offered an alternative explanation for why, absent corona, higher antennas might well experience more noise. True, but a height change of just a few meters on a building or tower hundreds of meters tall makes a big difference as do sharp compared to blunt points on an antenna. During a rainstorm, when most people complain about corona, droplets from the very same sources are hitting lower and upper antennas. The noise does NOT follow the pattern or rate of raindrops hitting the antenna, and the upper antenna is always significantly noisier than the lower antenna. Actual precipitation (rain, snow, hail) is not needed for P-noise. Of course not. It is a voltage gradient problem. Moving dust particles can carry charge and become charged. The noise does follow the "pattern of the particle rate." I've never seen it do that. But I'll keep watching for it. P.S. Some months ago you asked about V antennas for low HF or MF use involving a 300 foot tower. I found that an interesting topic and did some analysis, which I tried to sent to you. Unfortunately, the E-mail address did not work. That's because the email address listed by Google for me is a dead address. If it was live, it would be useless with spam and virus. 73 Tom |
H FIELD ANTENNAS?
Dear Tom:
Thank you for your ideas and the reference. Let us leave it that we see things differently. Readers have the ability to learn from contrasting each of our viewpoints. I have always included my E-mail address in my communications. I must to bed - tomorrow is the last lab day of the semester and I anticipate many questions directed to the proximate final exams. 73, Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: wrote in message ups.com... J. Mc Laughlin wrote: It appears that two noise mechanisms exist. The two are P-noise and corona noise. A receiver will experience close to white noise in both cases. However, corona noise tends to be accompanied by sudden stops and starts and P-noise starts with a sequence of perceptibly time spaced pops that increase in rate. Pops are caused by something charging and flashing over. All it takes to eliminate pops is a leak resistance or a leak choke slow enough to keep the antenna from charging. I've never heard the slow popping noise called P-static by anyone I know, but that doesn't say some people don't call it that. I have dipole high in the air, and on a clear day with a fair breeze they will knock someone right on their butt if the feeder is unhooked and the antenna allowed to charge. It does that dust or no dust, although nasty weather seems to greatly increase charge rate. It's easy to see why that happens. http://www.who.int/peh-emf/publicati...d_Exposure.pdf There is a significant electric field as we increase height even in fair weather. Even though that is a very high impedance field, it doesn't take air movement to charge a high conductor that is well-insulated. I have offered an alternative explanation for why, absent corona, higher antennas might well experience more noise. True, but a height change of just a few meters on a building or tower hundreds of meters tall makes a big difference as do sharp compared to blunt points on an antenna. During a rainstorm, when most people complain about corona, droplets from the very same sources are hitting lower and upper antennas. The noise does NOT follow the pattern or rate of raindrops hitting the antenna, and the upper antenna is always significantly noisier than the lower antenna. Actual precipitation (rain, snow, hail) is not needed for P-noise. Of course not. It is a voltage gradient problem. Moving dust particles can carry charge and become charged. The noise does follow the "pattern of the particle rate." I've never seen it do that. But I'll keep watching for it. P.S. Some months ago you asked about V antennas for low HF or MF use involving a 300 foot tower. I found that an interesting topic and did some analysis, which I tried to sent to you. Unfortunately, the E-mail address did not work. That's because the email address listed by Google for me is a dead address. If it was live, it would be useless with spam and virus. 73 Tom |
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