[RFI] Strong RFI on 2m

[nlsa at nlsa.com]

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