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

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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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

wrote:
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


I think the precipitation static talked about is
caused by the accumulation on the antenna of
charges carried by precipitation particles (e.g.,
snow). Apparently this is a common problem on
aircraft antennas, and hence the interest in LORAN
antennas with better immunity to the accumulation
of precipitation charges.

Doesn't sound like a simple antenna geometry issue
and it doesn't sound like a corona issue.

Which is not to say it isn't all hype, but
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?

Chuck

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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

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.

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

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

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.

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