Identifying QRM on 70 CMS

Discussion in 'Interference Problems' started by G6SPG, Oct 6, 2018.

  1. G6SPG

    G6SPG New Member

    Hello Everybody,
    I have recently started to experience local interference on 70 cms.
    It is in the form of a pulsating carrier, which i possibly believe to be eminating from a house at the rear of my property. The signal is about 100kc wide and centres around the FM calling channel 433.500

    I have placed a video on Youtube with the hope that someone has also experienced the same kind of qrm



    I would appreciate any help in this matter

    73 de G6SPG

    Paul
  2. Ken G3SDW

    Ken G3SDW Moderator

    Hi Paul, i would not call it pulsing but just bursts of something local to you, vicious and quite strong.

    With just the odd burst then it is impossible to say what it might be but what ever that maybe is not important, more to the point is were is it coming from.

    You say that it may be coming from a house at the rear of your property, why do you think that this maybe the case??

    To make 100% sure that it is outside your property then you must turn off your own mains supply at the main breaker and monitor on a hand held RX, if not then you will be chasing your tail and go round in circles.

    Let us know how you get on as i am always here to help.
  3. G6SPG

    G6SPG New Member

    Hi Ken,

    thanks for the reply, sorry I should have already mentioned the fact I have already took my property out of the equation, basically it was the first thing that I did.
    Have monitored both walking with a handheld and also mobile and the signal does tend to peak at a certain section of the road at the rear of my property.

    The power level is probably only milliwatts ? Have also had a fellow Amateur monitoring the frequency who has a house located near the end of this particular but not able to pick it up.

    Regards

    Paul
  4. Ken G3SDW

    Ken G3SDW Moderator

    Well then you need to confirm as much as you can that it is the suspected house and then knock on the door and in no way accuse just ask for there help in trying to locate the problem, even letting them hear it for them selves.

    They may well assume you are talking about CB so try to explain that you are licensed by Ofcom to operate your radio equipment, in may cases when radio is mentioned then there is an assumption that it is CB.

    Let us know how you get on and i know that knocking on doors is not what we want to do but until you do it will not go away, whoever it is will not have a clue that they are causing a problem so i am sure they will listen and help all they can.
  5. Ken G3SDW

    Ken G3SDW Moderator

    Hi Paul, just wondering what the latest is on your noise problem.
  6. G6SPG

    G6SPG New Member

    Hi Ken,

    Sorry for the delay in replying, I'm afraid the QRM problem has had to be but on the back burner for a while.
    I have been away from home and pre occupied with some serious family matters.

    I will keep you updated when i get nearer to resolving the problem.

    73 Paul
  7. Ken G3SDW

    Ken G3SDW Moderator

    OK Paul stay strong.
  8. vu2nan

    vu2nan New Member

    Hi OM Paul,

    The 432 MHz band is a shared one with Radio Amateurs having secondary status!

    73,

    Nandu.
    Ken G3SDW likes this.
  9. Ken G3SDW

    Ken G3SDW Moderator

    Nandu, we are fully aware of this in the UK and his problem is nothing to do with anything shared locally to him.
    Last edited: Nov 13, 2018
  10. vu2nan

    vu2nan New Member

    Thank you for the information, OM Ken.

    73,

    Nandu.
  11. Ken G3SDW

    Ken G3SDW Moderator

    73 from the UK
  12. G6SPG

    G6SPG New Member

    Hi Ken,

    its been quite a while since my initial post, just recently the QRM has spread to another spot frequency further up the band.
    its basically the same time of interference, wide banded (about 100 khz) centering on 433.900 and obviously coming from another location.

    I emailed in a report to Ofcom, and got a prompt reply within 30 minutes, As we are Secondary users of this part of the Radio Spectrum, they would not be willing to take my report and therefore closed the case.

    Regards

    Paul (G6SPG)
  13. Ken G3SDW

    Ken G3SDW Moderator

    Hi Paul, thanks for the update.

    Well that is exactly what i would expect Ofcom to say, it is true but you would hope that as there are other users then they would want to help, not just you, but others too, it could affect them being some channels are used by the military.

    Have you tried to DF it, being 70cm then should not be a problem, initially thats all Ofcom would have to do, after all until it is located then nothing else will happen.
  14. G7RUX

    G7RUX New Member

    Our secondary status on 70cm does lead to a few problems but most of those are resolvable, one way or another.

    However, there is a major problem in 70cm which is likely what the original poster, G6SPG, is seeing...a particular allocation is for "non-specific short range devices" which falls in 433.05-434.79 MHz. A particular item to note is that many remote-control car alarm key fobs, centred around 433.920 MHz, obviously appear all over the place and, although they radiate only a few milliwatts, can cause all manner of irritating interference. Lots of other SRDs use the same band so one can often hear bursts of interference.
  15. Ken G3SDW

    Ken G3SDW Moderator

    This thread has been going since October 2018, so would have thought by now would be resolved, but as Ofcom will not get involved then you have to get out there and locate it your self, being 70cm then that should be quite easy, thats assuming that it is top priority.

    I or the society cannot do any more than just advise.
  16. G7RUX

    G7RUX New Member

    Hi Ken,

    The point here is tht there is likely nothing to be done as the interference is from permitted Short Range Devices with which we share part of the band.

    Jason G7RUX
  17. Ken G3SDW

    Ken G3SDW Moderator

    Yes Jason, this should be know by most amateurs as it has been the case for some time now, this is why Ofcom will not get involved.
  18. G7RUX

    G7RUX New Member

    Indeed. However OfCom aren't doing themselves any favours by not explaining their reasoning...had they just explained to the complainant the situation with SRDs then I feel quite sure he would have been satisfied and understood better what the issue is (and more importantly, what it isn't!)
  19. Ken G3SDW

    Ken G3SDW Moderator

    LOL thats quite a lot to ask from Ofcom!

    And as for favors then they do very little, if any, and not even to them selves.

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