I have been plagued by AM intermodulation products between 2 and 4 MHz. for
several years. I have verified they are not generated in my receivers.
Installed high pass and bandpass filters and this does not affect the level. I
have knocked the -10 dBm AM signals levels down to -90 dBm at the RX antenna
port.
With a handheld spectrum analyzer I have searched the neighborhood for the
source and the only potential source I have come up with is a High Voltage
transmission line that runs about 500m north of my tower. When directly under
one of the 3 parallel lines, I can detect the intermod products. If I connect
the telescopic antenna to transmission tower, the intermod product rises to a
-40 dBm. The lines are probably 30m overhead.
We are about 5-8 km from the AM transmission sites of at least 5 broadcasters.
The intermod is primarily 3rd order, 2F1+/- F2.
Has anyone else seen this before and if so, were you able to get it resolved?
Ed, VE4EAR
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