Mike,
The PN junction where the mixing is occuring may not be in your antennas
but rather close to you. A metal fence or other object near you could
have a poor connection and be mixing signals strong enough to excite it.
The most likely places to look for external intermod is either close to
the transmitter or close to the receiver. Since others are hearing the
interference it could be close to the transmitters. Time to start
mapping it out, working your way away from your antennas. Enlist the
others in the area to see if you can identify an area where it is
strongest. Go portable and see if it disappears as you get away from
your station.
A directional antenna would be nice so you can head in a logical
direction rather than wandering. Do your beams, Beverages, and shorty
yagi give you any signal strength indications that indicate a particular
direction.
Earl
N8SS
----------------------------------------------------------------------
Message: 1
Date: Mon, 23 Oct 2006 16:25:05 -0400
From: "W9RE" <w9re@comcast.net>
Subject: [RFI] Intermod/Rectification
To: <rfi@contesting.com>
Message-ID: <NCBBIPEKMKEIENBFHFHJKEAEJFAA.w9re@comcast.net>
Content-Type: text/plain; charset="iso-8859-1"
I have a few loud (s9 to 20db over) intermod AM broadcast signals on
3640
and 3690 and these signals are heard on the Southside of Indianapolis
by
several other hams (at a lower level). My problem is that these signals
pulse to 20db over 9 and sound like I have a loose connection someplace
that
is causing rectification (which also causes other images across the
band).
I cannot track down the loose connection. I?ve tried monitoring SWR
while
transmitting, monitoring with a MFJ-259B, listening to the antennas with
a
pair of headphones (like a crystal radio with/without a diode),
monitoring
with a scope, monitoring with an analog AC voltmeter, transmitting into
antennas and listening on others, etc. with no luck. I have three 80
meter
antennas- a 40 meter double extended zepp, a sloping V Beam (both these
fed
with open wire line) and a shortened 2 element yagi, the noise is
loudest on
the zepp and the V Beam. I also notice the noise on Beverages and short
vertical receiving systems.
At night the signal levels are not as strong (AM stations changing
power/pattern) and when it rains the problem is not observed.
Transmitting
on 160 with a KW stops the pulsing from S9 to 20 over but it returns
when I
stop transmitting.
Last week I thought I had isolated and found it when I was listening on
3690
to a pair of 10 meter yagis (that are not used very often) I found the
intermod to be S9 and pulsing but after disconnecting the antennas up on
the
tower the problem still remains on the other antennas.
Any suggestions as far as isolating the problem?
Thanks
Mike W9RE
------------------------------
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