W. Watson wrote:
I bought this antenna on a 30 day trial, and just got it about 12 hours
ago. So far I'm not at all impressed. I live about 150 miles from an AM
station, at 810, in the SF/SJ Bay Area, which has a marginal signal, but
usually listenable. Putting a new PSU in a PC about a month ago
increased the noise in AM radios 70-100' from the PC to an almost
unacceptable level. I had hoped the antenna would boost the signal
enough to knock down the noise. There are times when I can get a good
signal from the station, but certainly less frequently than before.

The antenna consists of three parts: a 600-1800 KHz control dial, a
ferrite antenna and something called the antenna element. The latter is
about 8" long by 3" by 1.5" (high). The idea is that one puts the
ferrite antenna very near the radio and the antenna element in some
other spot, then adjusts the control dial to the max strength. I detect
zero change in any AM signal from the (C. Crane) radio anywhere on the
dial. The antenna element can be grounded. I modestly did this by
hooking a wire (alligator clips) from the element to the ground socket
of an AC outlet (nail in the socket). No change. BTW, when I was doing
the experiment last evening, the signal was pretty decent during that
period. In fact, quite listenable. All this without the device though.

I'll continue to experiment, but so far not so good. Comments?

I'd change the power supply to a better brand.

Generally if you have atmospheric or man-made noise increasing the
antenna efficiency is just going to increase the noise along with the
signal.

You could try to make a directional antenna; this would increase your
desired signal more than your noise.

The antenna would have to be big, however. The wavelength at 800kHz is
somewhere around 370 meters and you'd need to use around 1/4 of this.

You could try to feed power supply noise to the radio antenna at just
the right amplitude and phase to null it out. This would be a good
subject for an undergraduate or even a Master's thesis in EE but
probably not a good thing to do in practice.

You could attempt to shield it. Rat Shack has some clamp-on ferrites,
you could put one of these on your power cord close to the end that
plugs into the power supply. You could also make sure that the PC case
is well shielded.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

"Tim Wescott" bravely wrote to "All" (29 Nov 05 09:16:58)
--- on the heady topic of " C. Crane's Twin Ferrite Antenna"

TW From: Tim Wescott
TW Xref: core-easynews rec.radio.amateur.antenna:220543

[,,,]
TW Generally if you have atmospheric or man-made noise increasing the
TW antenna efficiency is just going to increase the noise along with the
TW signal.

TW You could try to make a directional antenna; this would increase your
TW desired signal more than your noise.
[,,,]


I wonder if it would help putting up a short vertical and summing its
signal with such polarity that it cancels the noise from the main
directive antenna? This on the theory that most man-made noise is
by its nature vertically polarized.

A*s*i*m*o*v

.... If you're not making waves, you're not rowing the boat

"Tim Wescott" wrote in message
...
W. Watson wrote:
I bought this antenna on a 30 day trial, and just got it about 12 hours
ago. So far I'm not at all impressed. I live about 150 miles from an AM
station, at 810, in the SF/SJ Bay Area, which has a marginal signal, but
usually listenable. Putting a new PSU in a PC about a month ago increased
the noise in AM radios 70-100' from the PC to an almost unacceptable
level. I had hoped the antenna would boost the signal enough to knock
down the noise. There are times when I can get a good signal from the
station, but certainly less frequently than before.

The antenna consists of three parts: a 600-1800 KHz control dial, a
ferrite antenna and something called the antenna element. The latter is
about 8" long by 3" by 1.5" (high). The idea is that one puts the ferrite
antenna very near the radio and the antenna element in some other spot,
then adjusts the control dial to the max strength. I detect zero change
in any AM signal from the (C. Crane) radio anywhere on the dial. The
antenna element can be grounded. I modestly did this by hooking a wire
(alligator clips) from the element to the ground socket of an AC outlet
(nail in the socket). No change. BTW, when I was doing the experiment
last evening, the signal was pretty decent during that period. In fact,
quite listenable. All this without the device though.

I'll continue to experiment, but so far not so good. Comments?

I'd change the power supply to a better brand.

Generally if you have atmospheric or man-made noise increasing the antenna
efficiency is just going to increase the noise along with the signal.

You could try to make a directional antenna; this would increase your
desired signal more than your noise.

The antenna would have to be big, however. The wavelength at 800kHz is
somewhere around 370 meters and you'd need to use around 1/4 of this.

The ferrite antennas are already directional. That is one of their
advantages.

You could try to feed power supply noise to the radio antenna at just the
right amplitude and phase to null it out. This would be a good subject
for an undergraduate or even a Master's thesis in EE but probably not a
good thing to do in practice.

These devices are well known and sold at least by 2 ham manufacturers- MFJ
and Timewave(?).

Dale W4OP

Tim Wescott wrote:

W. Watson wrote:

I bought this antenna on a 30 day trial, and just got it about 12
hours ago. So far I'm not at all impressed. I live about 150 miles
.... snip

during that period. In fact, quite listenable. All this without the
device though.

I'll continue to experiment, but so far not so good. Comments?


I'd change the power supply to a better brand.

Generally if you have atmospheric or man-made noise increasing the
antenna efficiency is just going to increase the noise along with the
signal.

You could try to make a directional antenna; this would increase your
desired signal more than your noise.

The antenna would have to be big, however. The wavelength at 800kHz is
somewhere around 370 meters and you'd need to use around 1/4 of this.

You could try to feed power supply noise to the radio antenna at just
the right amplitude and phase to null it out. This would be a good
subject for an undergraduate or even a Master's thesis in EE but
probably not a good thing to do in practice.

You could attempt to shield it. Rat Shack has some clamp-on ferrites,
you could put one of these on your power cord close to the end that
plugs into the power supply. You could also make sure that the PC case
is well shielded.

I tried the RS ferrites and they made no change. I even took barbell weights
and put them on the AC line of the PC. Zippo. If I hadn't already spent $60
for the new PSU six weeks ago, I might think of buying a much better one.

In some way this may be circuit dependent. I do believe I plugged in my
other PC to the same socket and had the same experience; however, when it's
plugged into its normal socket, there is no noticeable change.

Interestingly, bad weather moved in yesterday and today, and reception from
the station has been quite good with the normal antenna. This stuff can get
pretty strange.

--
Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

Traveling in remote places in the winter. What's the best
tool to carry with you? An axe.
-- Survivorman, Discovery (SCI) Channel

Web Page: home.earthlink.net/~mtnviews

W. Watson wrote:

In some way this may be circuit dependent. I do believe I plugged in my
other PC to the same socket and had the same experience; however, when
it's plugged into its normal socket, there is no noticeable change.


Grounding issue?

On Wed, 30 Nov 2005 02:54:34 GMT, "W. Watson"
wrote:

Interestingly, bad weather moved in yesterday and today, and reception from
the station has been quite good with the normal antenna. This stuff can get
pretty strange.

Classic indication of a bad ground, or a ground loop.

73's
Richard Clark, KB7QHC

Richard Clark wrote:

On Wed, 30 Nov 2005 02:54:34 GMT, "W. Watson"
wrote:


Interestingly, bad weather moved in yesterday and today, and reception from
the station has been quite good with the normal antenna. This stuff can get
pretty strange.


Classic indication of a bad ground, or a ground loop.

73's
Richard Clark, KB7QHC
If so, how do I track it down?

--
Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

Traveling in remote places in the winter. What's the best
tool to carry with you? An axe.
-- Survivorman, Discovery (SCI) Channel

Web Page: home.earthlink.net/~mtnviews

On Wed, 30 Nov 2005 03:44:17 GMT, "W. Watson"
wrote:

If so, how do I track it down?

Hi OM,

You have already related other experience where you shared the same
circuit as a noisy source (sharing the same circuit is easily
identifiable as being on the same breaker). Moving to another circuit
can be a solution. If it provides relief, then noise was coming by
conduction (through the wires) rather than radiation (over the air).

Insofar as your specific weather related symptoms, this is usually
related to a loose and corroded ground connection. The first place to
start is with your panel's service ground. If you have other ground
rods, then check them and INSURE they are also connected to the
service ground.

In your shack, do not daisy-chain grounds - use a star configuration.
However, you will probably still have mixed grounds with equipment
interconnections (and some of them are obvious and in your face and
are still invisible). That is OK if you also have the individual
equipments grounded in that star configuration. One of those
invisible gotchas is the equipment interface to a computer, with a
dial-up modem, its connection to the phone line and its own ground
(if in fact it exists). This ground path is one you stare at every
day and never see - unless lightning is looking for ground in through
it and into your shack.

To "track it down" requires that you pull every plug, break every
breaker and listen (you will need a battery powered, ungrounded
receiver that exhibits the problem to do this). Replace each one at a
time until you re-achieve your problem - take one step back and focus
there.

73's
Richard Clark, KB7QHC

In article t,
W. Watson wrote:

I tried the RS ferrites and they made no change. I even took barbell weights
and put them on the AC line of the PC. Zippo. If I hadn't already spent $60
for the new PSU six weeks ago, I might think of buying a much better one.

Ferrites clamped around the power cable will help with common-mode RF
noise. They won't do anything to help cancel out differential-mode
noise.

It'd probably be beneficial for you to try to get a robust powerline
noise filter. These will filter out both common-mode noise, and
differential noise as well.

Unfortunately, it's possible that the new power supply is radiating RF
directly, rather than feeding it back into the mains. If so, nothing
other than replacing it, or switching to a PC case with better
shielding, is likely to help the problem.

--
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!

Dave Platt wrote:
In article t,
W. Watson wrote:


I tried the RS ferrites and they made no change. I even took barbell weights
and put them on the AC line of the PC. Zippo. If I hadn't already spent $60
for the new PSU six weeks ago, I might think of buying a much better one.


Ferrites clamped around the power cable will help with common-mode RF
noise. They won't do anything to help cancel out differential-mode
noise.

Differential mode radiation is almost never a problem in situations like
this. The differential mode component of the noise, by definition, is
from equal and opposite noise currents on the two conductors (of the
power line, for example). For this mode, the conductors comprise a
transmission line, and radiation will be extremely small because the
fields from the two very close and parallel conductors are equal in
magnitude and opposite in direction.

Ferrites are a good suggestion, but the ones commonly used for RFI
suppression are of a ferrite type which doesn't have an awful lot of
attenuation as low as the AM broadcast band. Best would be some
Fair-Rite 70 series, or other ferrite with an initial permeability of
several thousand. Best would be to get a large core and wrap multiple
turns on it with the power cord, as close to the PC as possible. This
way, you get a lot more impedance than clamping cores onto the wire,
since the impedance is proportional to the square of the number of
turns. That is, 10 turns on a single core gives you the same impedance
as 100 of the same cores clamped onto the cable.

It'd probably be beneficial for you to try to get a robust powerline
noise filter. These will filter out both common-mode noise, and
differential noise as well.

A good power line filter isn't a bad idea, but differential mode
filtering won't make any appreciable difference.

Unfortunately, it's possible that the new power supply is radiating RF
directly, rather than feeding it back into the mains. If so, nothing
other than replacing it, or switching to a PC case with better
shielding, is likely to help the problem.

To radiate any significant amount of energy requires some sort of
antenna, so a power supply won't radiate much on its own. The trick,
then, is to prevent the noise from getting from its source to the
antenna. The most likely antenna is the power line, but any other wires
connected to the computer can also serve this function. I'd start by
disconnecting everything from the computer except the power line,
getting the noise down with ferrites or a power line filter, then
connecting one thing at a time and applying ferrites to the other wires
as required. If wires inside the computer are acting as the antenna, the
computer box should contain the noise to a high degree -- if you still
have noise with only the power line connected and filtered, check the
integrity of the computer case. Look for any seams that don't have good
metal-to-metal contact between pieces.

Roy Lewallen, W7EL