EMC on 2m - 144,725 & 145,725mhz?

Discussion in 'EMC Matters' started by Syzygy, Aug 7, 2016.

  1. Syzygy

    Syzygy New Member

    Hi,
    I'm new to the forum and got my Foundation licence in September 2015.
    Just lately especially on a sunday when I listen to the RSGB news that is transmitted via the GB3NC repeater at St Austell, in Cornwall at 9.30am, I am receiving very bad EMC from a localised source.

    It starts around 7am and then stops at 10am? It interferes with the GB3NC repeater on 145,725mhz and also on 144,725mhz? No other frequency is affected. I also listen in on the GB3SI repeater at Poldhu on the Lizard, and occasionally it happens there too on 145,625mhz. It has been known also to happen on 145,800mhz when listening in on the ISS but very rarely?

    I was considering building a EMC detector which would be very localised to this property or within say a 50m range, would this detect the source?

    I live right next to a transformer mounted on 2 poles which are approximately 20 meters from my shack, but they don't seem to be the cause as it would be constant??

    Other than the EMC detector I might build, is there any other way I could pinpoint this problem, I am disabled and unable to walk far or climb hedges and fences!!

    Here is the link to the home made EMC detector.

    http://www.popularmechanics.com/hom...lectromagnetic-interference-detector-8831727/
  2. Ken G3SDW

    Ken G3SDW Moderator

    Not sure of your name but welcome to the forum, would be nice to know your call sign.

    You say that this problem is on several repeaters but don`t say if it is only there or all over the 2m band.

    Do you belong to a local club by any chance? as i am sure they can help you locate were the problem is coming from as it will need some leg work and that i understand you cannot do.

    Yes i am sure you are correct in saying it cannot be the overhead power system that you have there.

    I know this may sound silly but have you proved that it is not coming from your own property by powering down at the main switch board and monitoring with a battery operated receiver? you will need to do this as if you have to call on Ofcom then if they find that it is then you will get a hefty bill in three figures, we don`t want that do we.

    Come back to me with some answers to my questions and we will take it from there.

    73

    Ken
    G3SDW
    RSGB EMC Help Desk
  3. Syzygy

    Syzygy New Member

    Hi Ken,

    The name's Gerry MK6FVC or M6FVC after 31st December...

    The EMC starts early and continues for around 3 hours? Very sporadic at times... but recently it's been happening more often Sunday Mornings before, during and after the RSGB news?
    I've tried all the suggestions as you mentioned so it cannot be something produced from the bungalow? I was a member of CRAC (Cornwall Radio Amateur Club) but found the 50 mile round journey too exhaustive. I have written to the Guys at MCBARG who run the repeaters at St.Austell and they say the new repeater installed was working fine, as is the repeater at Poldhu.

    Distance is the problem, I guess I haven't asked as these guys work etc and asking them to come all the way out here is probably asking too much? I have a fun cube Dongle and into Radio meteor scatter, using 2m Yagi and working off the Graves Transmitter in Lyon France on 143048Khz.. and was encountering the same problem too? Sometimes it was OK others I just couldn't work the FCD, too much EMC coming from somewhere?

    I'll try attach a MP3 recording of the EMC perhaps a trained ear might recognise what it might be? About a mile from here id the NATS station) National Air Traffic service which transmits for in bound aircraft from the atlantic. They did some upgrades about 10 months ago and during/after the work it started then... OFCOM were contacted and they run an enquiry with NATS and the contractors but I was told it wasn't them although my 2m Yagi has to point in their direction for Lyon.

    Today, there was EMC on 144,725mhz and 145,725mhz but no other frequency on the band? Poldhu on 145.625mhz was unaffected as was the rest of 2m - 70cms and HF Top band, down to 40 and 20m's.

    To me, it sounds like an electric motor??

    Anyhow, thanks for getting back to me Ken.

    Best wishes and 73's Gerry M6FVC

    Attached Files:

    • EMC.zip
      File size:
      217.8 KB
      Views:
      21
  4. Ken G3SDW

    Ken G3SDW Moderator

    OK Gerry,sorry for the mistake regarding your name.

    Can you see if this problem is any were else on the HF spectrum, no amateur bands but anywhere else on HF.

    As for a trained ear then today due to so many different types of RFI then that is not accurately possible but by just listening then there is a possibility that it could be a PLT device running in standby, if it is then you will hear it by listening outside the HF ham bands, as they should be notched on the HF bands.

    This could be coming from either of the two house that you mentioned and the owner(s) for one minute would not suspect that it could be coming from that sort of device.

    Some times they are left on 24/7 and sometimes they are turned off when not in use.

    I may be wrong but we have to start somewhere.

    Just looked at you shack picture and for an M6 you have a nice set up and some nice equipment, well done.

    73

    Ken
    G3SDW
  5. Syzygy

    Syzygy New Member

    Hi Ken,

    I haven't heard it on HF when the problem occurs? It just appears specific to 2m. I did a scan yesterday on HF - Top band down to 20m whilst it was transmitting but nothing untoward.

    I think you are right with it being localised and very close, got to be a house within a 50 meter area to me. I've been in contact with MCBARG (The St Austell repeater group) and it was suggested to leave my Yaesu 857D on 2m 145,725mhz continuously for the next two weeks and log any times and dates it happens to see if there is a pattern to it?

    Thanks for your kind comment, I would dearly love to progress on to the Intermediate level, but there isn't any clubs etc anywhere in Cornwall that will be running a course for the foreseeable future? I've contacted them all, it seems I will have to travel outside the county which could mean over a 100 mile trip just to get into Devon or beyond? I've contacted RSGB Southwest a while back about the problem, and was told that enquiries would be made, as yet I'm still waiting.

    I guess it's just a process of elimination slowly weeding out the problem... I'm certain in time I will find the source, it's a good thing it only happens sporadically and not all the time!

    Best Wishes

    73

    Gerry - M6FVC
  6. Ken G3SDW

    Ken G3SDW Moderator

    Ok thats fine Gerry, a good idea to keep a log of times when it is on, its rather strange that it is only on you local repeaters.

    You say about being local and you are right, in most cases it is closer to home that further away.

    Keep me updated with your progress and i am here to help at all times.

    73
    Ken
    G3SDW
  7. Syzygy

    Syzygy New Member

    I will do Ken, and thanks for your assistance...

    73's

    Gerry - M6FVC
  8. paulcornwall

    paulcornwall New Member

    Just to add to this, I've been having problems too. This evening its been terrible on 70cm but also get EMC on 2m. I live approx 3 miles from Gerry so unsure if this is related in any way. Tonight has been very bad with the pulsing sounds very pronounced. I took a drive around St Just and into neighbouring villages and it was still heard, bare in mind this is now on a different rig and antenna. Here is a video clip of the noise, please let me know if you can assist
    Many thanks Paul.
  9. Ken G3SDW

    Ken G3SDW Moderator

    Well Paul it seems as that it is not just local to you and Gerry but somewhere is a radius of say about 5 miles.

    Is it still there 24/7? take a good ride around to get some idea of its location, have you got any mobile phone masts in the locality?

    As i said to Gerry keep a log, i did ask Gerry but he has not come back to me so far.

    We may have to get Ofcom involved at some point so a log could be very useful

    As for what it is well for sure it is something that has a clock so not just your normal RFI generator.

    Keep me updated if you could, would not want you to suffer in silence, always here to help at all times.

    73

    Ken
    G3SDW
  10. paulcornwall

    paulcornwall New Member

    After going mobile last night I tried to get an idea of the how pronounced this QRM is. I have attached a map which shows where this particular QRM is audible (shown on red path) while the blue path shows reduced/no QRM

    Attached Files:

  11. Ken G3SDW

    Ken G3SDW Moderator

    OK Paul well it is not just one of your neighbours is it for it to cover such a wide area.

    I will show all the details to the other members of the EMCC to see what they think and i will get back to you asap.

    73

    Ken
    G3SDW
  12. paulcornwall

    paulcornwall New Member

    FYI there are two- three towers within this radius. I believe there mobile phone masks but can't be sure. The pulse is also audible when no rx is being received, however seems less dominate. Here is a short video of that
  13. Ken G3SDW

    Ken G3SDW Moderator

    Thanks Paul, i have copied all the info on to our EMCC reflector.

    Have you tried to see what signal strength you get when close to either one of the three masts, i would say they are the most lightly candidates.

    73
    Ken
    G3SDW
  14. paulcornwall

    paulcornwall New Member

    Sorry for gate crashing your thread Gerry, but hopefully some resolution may be found from this.

    Ken, the qrm is lounder on the south side of the map, I'm guessing this is because this is where the masts are located and also an number of wind turbines. I've marked on the map the location of the masks and attached pictures on them that may of be use.
    Many thanks for looking into this issue, we seem to be plagued with interference down this way! :(

    Attached Files:

  15. paulcornwall

    paulcornwall New Member

    oops, missed one.

    Attached Files:

  16. Ken G3SDW

    Ken G3SDW Moderator

    Cheers Paul.

    73

    Ken
  17. G3NYK

    G3NYK New Member

    It is a bit confusing as we now have two reports of interference which seem to be different sources in the same area
    First Paul's report on 70cms of a pulsing sound. This reminded me of the Syledis locator system, though I have not heard it for a while. A quick check on Utube and the example there has a much faster pulse rate but was on 70cms. The facr that it is appearing on top of several different frequencies does suggest it "may" be intermodulation created by a strong signal entering your rig but not necessarily on that frequency. You posted a clip of it on a local repeater. Is it audible when the repeater is off? Is it audible on the input channel?

    If we assume it might be a locator beacon.....do you have any coastal protection works on that section of the coast? or are there any off-shore wind turbine errection jobs in the area....the slower pulse might indicate use a a greater range. If you can cut a simple horizonal dipole for 70cms connect it to a lengthe of RG58 with a choc-block (electrical screw terminal block) ...crude but effective....put it on a bit of broom handle or similar to act as a handle. Connect to your rig and try and find a position where the pulses are minimised. The direction of the source is off the end of the dipole elements. If this works it will give you a clue where the source of the pulses is. You then need to repeat that from another location so the lines given on the map by the dipole orientation cros at an angle nearing a right angle. Where they cross "may" indicate the source. Note that the pulse source may not even be in 70cms if it is causing intermodulation. Funcubes are not too good with this sort of problem....however if you reduce the signal into the receiver the interference may go leaving a wanted but acceptable signal readable (this is a feature of intermodulation)

    More ideas later when I get a better feel for the effects.

    Alan
    G3NYK
  18. G3NYK

    G3NYK New Member

    Gerry's interference seems to be only on 2m I need to get a feel for that I will look at the posted files

    Alan
    G3NYK
  19. paulcornwall

    paulcornwall New Member

    Thanks Alan for your comments. I must make it clear that the pulsing on 70cm is completely separate to the local issue I have on 2m. The pulsating sound on 70cm can be heard constantly, it also covers a wide radius (approx 2miles) unlike the other issue on 2m which is in my house and localised.
    The 70cm pulse is audible no matter if the repeater in open or closed, it is more pronounced when the repeater is open but is always there. Changing the frequency by 25hz makes it disappear and seems audible only on 433.375. I am unsure regarding coastal protection works (?), and theres no offshore wind turbines, although theres plenty on shore.
  20. G3NYK

    G3NYK New Member

    Ok Paul first the pulsing from the "Pt2" it would seem that the pulse is not on the repeater channel either input or output. I would guess its intermodulation with either your rig or the repeater, If the pulsing is not heard by stations outside your mapped area this would help confirm it. I know the problems as I live abour 400m from the local police Div HQ which had a channel on 146.600 (I think it was) and I needed filtering to remove it. What we need to di is find out what the "real" frequeny of the pulsing is. This will require tuning through all the channels you have with a receiver you should find a signal somewher that completely quietens the audio when the pulse is transmit( notice that on the Pt2 clip with the repeater off you are hearing pulses of noise and inverse too....this is the pulse quieting your receiver by desensing the RF stage.) You may need to emply a wide range receiver like a funcube or SDR play to find the real frequency of the pulser. If youcan do that we can recomment a filter to fit to your aerial to reduce it to an acceptable level.

    Alan
    G3NYK

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