[RFI] Strong RFI on 2m

[David Eckhardt]

I suspect what you are experiencing is broadband noise from solid state
transmitter PAs.  During the days of vacuum tube amplifiers for commercial
broadcast this was much less of a problem.  However, the newer solid state
PAs produce *much* more broadband noise than their older vacuum tube
counterparts.  There likely isn't much you can do about it other than not
point your antenna(s) at the source(s).   The noise is there and all the
filtering in the world is not going to eliminate it.  Not what you want to
read for an EME setup.

With that many sources, both FM and TV, I doubt you would be able to
convince all of them to install aggressive BPFs on their outputs.  Best
case might be only one or two of the broadcasters are responsible, but I
doubt you should be so lucky.

Dave - WØLEV

On Wed, Dec 22, 2021 at 3:18 PM <nlsa at nlsa.com> wrote:

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