Dear friends,
I have recently commissioned my 4-yagi 2m EME system. To my unhappy
surprise, I find strong RFI in the direction of a large commercial broadcast
tower 3.5 miles away. The noise is uniform across my 96-kHz passband, as if
the noise floor has been raised 20-30 dB. I don't detect any modulation or
other structure to the noise; it is wideband and constant. It affects my RX
in other directions via antenna sidelobes.
I have discounted fundamental overload to my system by placing a 2-cavity
bandpass filter in the RX line. It should attenuate everything outside the
2m band by at least 40 dB and yet there is no effect on the RFI noise. I
conclude that the noise is "real," in other words not an artifact of my RX
chain.
Questions:
* Should I expect modulation of some sort on spurious emissions from
TV or FM broadcast stations? (I have five TV and five FM transmitters within
a 5-mile radius).
* Other than the usual direction-finding, what else might I try to
investigate in order to identify the source?
Thanks for any suggestions -
Mike, W9IP
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