2m QRM ~145.5 and 144.25, 80kHz wide, sweeps 10kHz, 50Hz modulated

Discussion in 'Interference Problems' started by G4PLZ, Dec 4, 2017.

  1. G4PLZ

    G4PLZ New Member

    And I have spectrum + waterfall recordings of it larger than can be attached so I've just uploaded a shot of the spectrum. 2m QRM at G4PLZ 04_12_2017 17_04_19.png
    It sometimes drops down to the 144.13 region and eats up my EME. It is on a 90degree heading from my QTH.
    Before I start heading due east from here is there anybody who can look at the recorded data and tell me whether I should be looking for a pie shop or a nuclear power station?

    Pete G4PLZ
  2. GW4JQP

    GW4JQP New Member

    Hi Pete

    It looks a bit like the unlocked signal from a dirty switched mode power supply. A couple of days ago I saw a very similar signal wandering around 70.45MHz, but I haven't seen (or heard) it on 2m. DFing on an arc at some distance from your station might help you pin it down.

    Good luck,

  3. G4PLZ

    G4PLZ New Member

    Hi Peter

    Would't an SMPS show switching harmonics across the spectrum?
    The snapshot does not give any clear indication of how they scan ~12/15kHz down in frequency over 2 or 3 seconds (both are variable), only to snap back and wander down again; you can pick out the sweeps in the slow waterfall in the snapshot.
    In an SSB bandwidth I can see 50Hz modulation bars, AM demodulation has lots of nice, dirty 50Hz hum, while a 60kHz fast waterfall shows the 2/3second regular sweeps followed by a snap back. These 'wobblies' are in only two parts of 2m - I have looked well outside the band on both sides but only these two appear.
    It seems to be on 24h and I think that it only appeared a few weeks back when the weather got colder.
    My yagi array has quite a narrow beamwidth and there isn't a lot due east of here except fields until the village of Felmingham so I assume it should be much louder there - or really loud further east in North Walsham. A drive around will show more.

    Cheers, Pete G4PLZ
  4. Ken G3SDW

    Ken G3SDW Moderator

    What ever it is guys and it is a great possibility that it is a SMPS, then mores the point is where is it located, as Pete has said a drive around is needed which will localise it, then doors will have to be knocked on, thats the hard bit.

    SDR`s are a great asset to us today but it will not show us where it is located and after all this is what we want to do, well what we really want to do is eliminate it.

    Keep the forum updated if you could Pete.
  5. Ken G3SDW

    Ken G3SDW Moderator

    Pete before i turn in for the night, one thought, have you turned off your mains supply and checked on a portable RX.

    You would be surprised on how many cases that come my way that turn out to generated by them selves.
  6. GW4JQP

    GW4JQP New Member

    Hi Pete

    I recall a couple of years ago a posting, not sure if it was on here, indicating that a pair of speaker leads appeared to be working as an antenna causing the interference to be transmitted as a modulated carrier on VHF rather than by direct radiation. If you are some distance from your source, it may be something similar.

    As Ken says, knocking on doors is the hard bit. I was lucky once, by making myself very obvious in the street outside the source with an HB9CV and receiver, the interference disappeared. If only it was all so easy.

    On our local 4m net last night, three out of the four stations I was working disappeared below the noise floor when somebody switched on a very wide band noise source in the neighbourhood. Standing outside with a 4m yagi isn't quite so easy...!

    Anyway good luck

  7. Ken G3SDW

    Ken G3SDW Moderator

    It could be just coming from anywhere but we as amateurs always assume that i could not be us, wrong, even i who advises on such issues 24/7 have been caught out in the past so i always suggest that powering down your own house in the first instance will stop you chasing your tail.

    Just think what electronic equipment we have in our homes and compare it with what is in your neighbours, it has to be done.

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