RadioBanter - H FIELD ANTENNAS?

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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

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

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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

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.