TopBand: Re: AM Broadcast Interference

[David Kennedy]

To Ed--W0SD

You are experiencing a type of Top Band QRM which has baffled me
for years and I have yet to hear a reasonable explanation. I don't 
believe
that these "sigs", which are spaced every 10 Khz across the 160M band,
are either harmonics or "intermod". 

If you demodulate these sigs with an AM receiver you will hear a "gaggle"
of several AM B.C. stations on the same frequency. Like 910 + 920 = 1830,
970 + 960 = 1830, 900 + 920 = 1820, etc., etc.

I have spent many hours constructing low pass filters and selective 
tunable Cohn-type filters (see ARRL Handbook) with no "appreciable"
effect on these "signals". I am skeptical about one explanation that has
been offered, i.e., diode detection and retransmission due to corrosion
in the joints or connections of gutters, down spouts or power lines in
the area. This theory doesn't seem to hold water when I observe the
"signal" strengths vary widely according to which of several beverage
antennas are in use at the moment. 

I expect that some may believe that the re-transmission of these "sigs"
may be caused by my own 160M tower. One of my 2-wire Beverage
antennas is fairly close to my tower (100 ft. or so) but "the sigs" are
not
stronger on this beverage. I have to conclude that there is some kind of
external mixing going on but how these "sigs" are getting into my
receiver remains a mystery to me.

All I can say is -- don't waste your time and effort building low pass or
band filters expecting to eliminate these "sigs". Some people evidently
don't hear them because they operate on the same freqs.  Are these the
people with no towers--just wire antennas? 

One question for Ed. Are you sure that these "sigs" started up after your
ice storm and were not there all the time? Like Ed--I would like to hear 
any plausible explanatrion for this "phenomenon".

73 Dave N4SU.

 

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