I am having a severe case of AM broadcast "intermod. 160 contest is this
week end and here in SD we are coming out of the longest ice problem I
can ever remember. Coming out of this ice problem I have developed AM
broadcast interference. Any suggestions would be appreciated so
hopefully I can get it cured before this Friday. I am about 40 to 50
miles from any AM broadcast stations. I can copy two of the stations on
160. One is WNAX on 570 and the other is KELO on 1320. I believe I can
hear a couple of more but have not been able to ID them.
I get the "intermod" starting above the broadcast band and it is every 10
khz on 160 so it is at 1.800, 1.810, 1.820 etc. It is about S-6 on a
TS-950 SDX. I also have it on my other HF radio an IC-736. I have
used about 30 db of attenuation and it is still there. I have fed the
antenna's into the RCV. antenna jack on the TS-950 SDX and it is still
there. I have hooked the feedline direct to the radio not going thru
any switches and it is still there. Based on this I believe it to be
external (coming from outside) and being it happened with the ice storm
it would seem to be a rectification problem but I'm trying to not close
my mind to anything.
When it started I had a lot of dipoles that came down and a couple were
wrapped around the guy wires. This past Friday I cleaned all this mess
up but the "intermod" is just a loud as ever.. I have 10 towers with
the tallest being 200 foot with a 160 dipole I just replace yesterday at
the top and I redid my 160 full size 1/4 wave vertical by replacing a
long mast with a couple of tower sections. The vertical has an
insulated base. I also have a dipole at about 90 feet. The "intermod"
is loudest on the high dipole, then the vertical and next the lower
dipole. On this past Saturday I installed 3 beverages that are about
600 foot long each and they use pre-amps and are terminated. Apparently
the wave front is different on the beverages as I can just barely hear
the "intermod" on the beverages. If I can't get this fixed by the week
end the beverages are really going to be key to hearing anything. I had
the "intermod" problem before I installed the beverages.
'
I am open to any suggestions on how to cure this. Here are some
questions I have. What would be the best way to Direction Find? Use a
small loop? With all the snow it is going to be hard to move even say
an IC-706 around but I can try with the 4 wheel drive pick up. What has
been the experience as to how far away this bad joint is assuming that is
what it is given the AM broadcast stations are between 40 and 50 miles
away. Would you suspect it is a bad joint on the power line or an
electric fencer as I can hear one a little bit. BTW I have no intermod
on 80 meters.
What has been the experience in "shaking things" and hearing the
"intermod" change in strength?
Ed-W0SD
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