I live in an area where several medium wave 50KW broadcast stations
are located, the closest plant being at most 10 miles away. There,
two stations are co-located on 670 and 780. I had broadcast QRM on
1980 when I was trying an untuned random wire antenna to a typical RF
preamp, in this case one made by ICE if I remember right. The problem
turned out to be a 50 KW station on 1160 mixing with another station
on 820. Any kind of matching network to 50 ohms for the antenna on
160 m. placed ahead of the preamp eliminated the problem. The
matching network acted like a band pass filter. A high pass filter
would have probably done the same thing. You have to put your
filtering ahead of the stage where the mixing is taking place.
73
Rob
K5UJ
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