(Not So) Random QRM during Nets etc.

Discussion in 'EMC Matters' started by Lin, Dec 26, 2018.

  1. Lin

    Lin New Member


    Up until recently I didn't have a problem.

    Every Tuesday evening I pick up a fellow operator and we go mobile to join a local 2m net. The reason is twofold; one to get both us out of the house (and we nip into the pub afterwards for a pint and a natter), but more importantly our net controller lives very close to my QTH and as the net is run on our local repeater, even with the power turned right down I run the risk of de-sensing his rx etc. - so mobile it is.

    Over the last couple of months the net control has reported sporadic but intense QRM during the net(s), primarily when he taking an over or returning to an operator. Generally, the rest of the net doesn't seem to be affected in anyway other than net controls transmission reducing in volume underneath 'hash'. Net control has his suspicions but has resisted investigating any further - for his own reasons.

    As I tend to operate VHF/UHF away from my own QTH most of the time, this problem hasn't been that much of a concern, although I did offer to assist Net Control in his investigations, if I could be of help.

    Today - Boxing Day, I tried to run a net on behalf of my own club, using a local repeater from my home QTH. I started the net at 1145 hrs and very shortly after (within 2 mins) the interference began and continued - on and off - for the next 30 mins, in a random manner.

    I have 18 repeater programmed into my Icom IC 207 dual bander and when I scrolled through them the signal levels dropped and rose again depending on which band I'm on, I.E. on 2m I have full deflection on the 'S' Meter and nothing on UHF - the noise was constant as I had the squelch wide open on both bands.

    I'm 99.9% sure this QRM isn't being generated from within my property. There is a further complication arising from another local operator, with whom it could be said, that both I and net control (along with the rest of the world - no joke) share some enmity.

    Rather than jump immediately to conclusions, I'd rather go down the 'process of elimination' route but due to the fact that the problem(s) only seem to arise during nets etc. and not every time even then, I'm left wondering what to do??

    One of my colleagues got a snapshot of the signal on his 991 (attached). I also have a video of the problem on my 207, but can't post it here due to limitations of the board etc.

    As I sit here and write this, the QRM has come back again - just when the repeater sent its ident, so I guess my next move is to speak to the repeater keeper(s).

    Any useful suggestions would be gratefully received.

    73's for now all. Lin

    Attached Files:

  2. Ken G3SDW

    Ken G3SDW Moderator

    Well first of all i need to know who we are talking to, ie call sign please and what repeater are we talking about.

    Before you start you must prove with out any doubt that the problem is not coming from your own property and to do this you must turn off your mains supply and see if the problem is still there by using a battery operated rig.

    The clip that you have attached does not tell me much at all, so can you enlighten me on what you are showing me.

    Do these tests and come back to me if you can.
  3. Hello there, I have just registered on the forums today, my name is Daniella Stewart, I live in Rochester in Kent in the Medway towns.
    My local club operates a daily net, by agreement on 144.650, the Raynet channel.
    In the last few weeks, we have been experiencing significant QRM on only this frequency, either side is clean.
    It is S9 plus, pulsing, and a few of us speculate that it sounds like a spurious signal or possibly a data signal generated by the Raynet service themselves.
    If anyone else has heard this, and has a theory as to its origin, I would be very grateful if they could comment.
    Thankyou very much,
    Daniella Stewart, M6OCX
  4. Ken G3SDW

    Ken G3SDW Moderator

    Daniella, does anyone else on the net who is using the that frequency get the same signal as you do, or is it just yourself.

    If not then i suggest that you turn off your mains supply and monitor that frequency with a portable RX to see if it is still there.

    Let me know what you find.
  5. Lin

    Lin New Member

    Hi Daniella (and Ken),

    I'll tell you the results of our investigations first, then offer what advice I can. First of all, I followed Kens advice and cleared my own shack!

    I turned the mains power off in the house and removed every single plug, I also turned off the solar panels on the roof. With the help of two TARS clubmates, Kerry M0KRE & Alan 2E0HRT, two radios were set up in the shack, to monitor noise levels at HF & VHF/UHF. We then proceeded to switch the power back on and replace the plugs one at a time, all the while Alan monitored the rigs in the shack (which were running on battery power for the test).

    Kerry & I worked our way around the house and back to the shack, with very little noise or interference making its presence known - which was both good and bad! Good cos I wasn't getting interference from something I owned, but bad as it looked like I was going to have do some investigations outside of my property!

    We made it back to the shack having plugged everything back in, even the solar panel regulator proved to insignificant with no discernable increase in noise levels across the HF/VHF/UHF spectrum - which to be honest we suspected to be a prime candidate.

    We moved on to reinstalling the plugs in the shack and it was only when Kerry plugged in a Palstar Switch Mode psu did things change significantly....... 1st of all, there was an almighty 'crack' as the plug went into the socket extension bar ('that didn't sound good' commented Alan) and then as soon as the Psu was switched on the HF rig went straight from S1 to S9+ of white noise!!!

    Had we found the culprit ? To right we had, further careful investigation found no further evidence of interference from any of the devices in the shack and around the property! I sincerely doubt I will be running an HF radio at the same time as my arc welder!

    Not only was the Palstar generating significant noise levels at HF, it was also creating interference on the VHF 2m band - starting at around S2 on my Icoms meter and rising slowly and significantly to S9+30 over a period of about 1-2 mins. It would stay at S9 for anything up to 15 minutes and then just as suddenly, drop away to nothing again! Giving the impression (to me at least) of some random - possibly deliberate - interference? Having removed the offending item from the shack and installed an SDR software package on my laptop (huge thanks to Matt & Kerry) I now have a largely interference free shack and the difference is noticeable, not least of which I can hear very weak signals again!

    So it would appear that my issues (locally at least) have been solved, the persistent abuse of the repeaters is also being investigated and the offenders will be bought to book for their actions! I am, as they say in the Army, once again a Happy Bunny :)

    Daniella, what can I say about your situation? Well it's a little different to my own, but first of all - it isn't 'a Raynet channel' - no such thing! The band plans published by the RSGB etal are for 'guidance only' and are not set in stone. You and your local club have just as much 'right' to use 144.650Mhz as anybody else, but of course adhering to the T&C's of your licence - which says you must not cause undue interference to other operators......... It can be regarded, at best, as a 'notified' frequency, to be used by Raynet teams nationally during exercises and other activities, but it's definitely not reserved just for them, the following link may provide useful reading, particularly para 3. ( https://rsgb.org/main/operating/band-plans/vhf-uhf/144mhz-band/ ).

    As you say its not only you who is suffering interference, then I suggest a collective survey might be on the cards! But before doing so - do exactly what I have done and make sure your own house is in order - tbh it only takes half an hour at most and if you do it as a club, helping each other, then it becomes a bit of a social activity too :)

    Once you've cleared every ones properties/shacks it might prove sensible to report back here to Ken and the team for further advice! A laptop and SDR dongle can prove useful, but something like a Yaesu FT 817 which runs on batteries proved invaluable to our investigations. I hope this help in some way.

    My grateful thanks to Ken for his advice and Kerry & Alan for their assistance in sorting out my home grown ECM issue!

    73's All. Lin. M0TCF (TARS Trg Tm & RSGB TtT).
  6. Ken G3SDW

    Ken G3SDW Moderator

    Lin you informed me that you had turned off your mains supply and the noise was still there, it seems not so.

    If you had then your problem would have been solved some time ago.

    I can only advise on the info given.
  7. Lin

    Lin New Member

    I agree, at the time I turned the power off previously, I wasn't using the Palstar PSU....

    73's Lin. M0TCF (TARS Trg Tm & TtT).
  8. Ken G3SDW

    Ken G3SDW Moderator

    Never assume always do it every time, make it a rule of thumb.

    Quite a few of cases that come my way are noises generated by the amateur them selves.
  9. Ken G3SDW

    Ken G3SDW Moderator

    Dannie, you say...

    "It is S9 plus, pulsing, and a few of us speculate that it sounds like a spurious signal or possibly a data signal generated by the Raynet service themselves."

    Does this mean that others can here it as well? if so what sort of distance would this cover?

    As for the Raynet Service generating it themselves well there us not such thing as the Rayent service other than volunteers helping in emergencies and various events.

    Judging by your QRZ.com page then i see you are in good hands with your other half who i am sure will help you solve your problem.
  10. Ken G3SDW

    Ken G3SDW Moderator

    Hi Danie, have you managed to get any further with your on 144.650Mhz at all as i need to update my report.

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