[RFI] FM modulated RFI on 3.885 and more

David Eckhardt davearea51a at gmail.com
Sun Feb 14 16:47:19 EST 2021

This goes back a few decades, but there were once several products that
turned your house wiring into data lines (early Ethernet).  They operated
on 80-meters.  They could easily be 'disabled' by running power on
80-meters from your transmitter / amp.  I went through two until I laid
down the law for the house.  Yes, they interfered quite badly on 75/80.

Another thought, from experience, are the mouse / mosquito electronic
repellents that you just plug into an outlet and let the RFI fly free.
They are still sold.  They were a bit more difficult to 'disable' with RF

Dave - WØLEV

On Sun, Feb 14, 2021 at 7:58 PM WHYTE <radiotrade at rogers.com> wrote:

> 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
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*Dave - WØLEV*
*Just Let Darwin Work*

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