FM RFI on 75m;
I recently have been hit with 24/7 RFI on frequencies from AM BC band up to
20m. The worst of it (S-9) seems to be in the 75m band, with a very “digital”
sounding, wide band “hash” on 3.885. It sounds FM modulated. It certainly, most
clearly demodulates when listening in FM mode. (On Yaesu FT-857d) . Example of
RFI groupings; 3.585, 3.620 to 3.665, 3.770, 3.880 to 3.905, 4.120 to 4.157 etc
etc..
As it increases and decrease from these frequencies, it’s strength gets weaker.
(S-7 to S-5)
I have eliminated sources from my own home per usual AC / battery cuts etc.
It is certainly coming-in off my 80m dipole (Fed with RG-6, with coax choke-
only at feed point). Shield is certainly picking up much of it . Coax runs
close to property line of abutting house.
Bottom line; I can’t find any typical household consumer devices etc., that
may use the 3.5 to 4.5 MHz, that almost certainly transmit in FM and digital in
nature. I have not yet found a “fundamental” frequency outside the HF
band..suspect is may be the 4.120-4.157 frequency.
Any ideas on which devices are suspect? ( e.g wireless thermometer, wifi AC
line extenders etc) ? I have a new neighbour who recently moved in and suspect
it’s from his home...but I have yet to DF (using FM mode- portable HF
receiver). AM receiver will work for tracking it, but it’s far less
distinguished from my normally very high RFI smog, so will take the FT 857
“backpack mobile” for Its FM.
Any source ideas ? I have never before encountered an FM modulated HF “Spectrum
killer” ...and right on The AM window :-(
Tnx for permitting my chatter...
Greg
VA3FAX
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