Telamon wrote:
In article . com,
"Steve" wrote:

Bob Dobbs EC42 wrote:
On Wed, 06 Sep 2006 17:45:13 -0700, Steve wrote:

've been experimenting some more with the ANC-4 / H-800 combination. I
now have the H-800 situated in a nice spot outdoors, and have noticed
something odd when it comes to eliminating noise. As soon as I turn on
the ANC-4, using the H-800 as the noise antenna, the noise is often
already minimized. For example, the noise level might immediately drop
from S6 to S3, and adjusting the noise gain and noise phase controls
will have little effect (good or bad) on this S3 noise level. This
doesn't happen everytime, but it happens a lot...most of the time.

If I then use a wire as my noise antenna, the noise level might drop one
or two S units as soon as I turn the ANC-4 on, but it takes some knob
twiddling to get the noise level down to the S3 reading that I get
automatically and immediately when using the H-800. And the best result
using the wire is always the *same* as the result I get straight away
using the H-800. Always.

I've puzzled over why this is. I think it must have something to do with
the fact that the H-800 has quite a bit more gain than the wire, making
it a better 'match' for the main antenna...which means a lot of the work
is done for me? This is just a guess.

You'll have to evaluate which provides the better NR;
the reduction from the loops null,
or the null from the inverse phasing.
If the loop is alredady nulling the noise source then it might not be
providing adequate noise signal to the ANC-4 for its inversion process,
in which case you might try peaking the loops noise signal.


--

Echo Charlie 42
San Diego, California

I don't think the problem is due to the orientation of the loop because
we're talking about something that happens all the time and not just in
relation to one or two particular signals. I'm just about convinced
that the H-800 is simply providing more signal than the ANC-4 can
handle. I haven't tried any form of attenuation yet, but am thinking
about how to arrange that.

You can build an attenuator of any value with three resistors in a metal
box with two appropriate connectors.

--
Telamon
Ventura, California

If you go inside the case of the ANC-4, it has a jumper you can adjust
that "places a high pass filter with at least 50 dB attenuation in the
stop band in series with the noise antenna." This is a pretty darned
neat feature, in my opinion. It doesn't make the H-800 work any better
as a noise antenna, but it does make some of the wires work a bit
better. Very nice.

With the high pass filter in series, I find that I more often get the
deepest nulls with the frequency range button in the "out" position,
even though this is, in theory, the position it should be in for
frequencies above 20 mhz. I'm not sure why this came about, but oh
well.

Steve
Steve