JT65 problems on 30m

Discussion in 'EMC Matters' started by M0XDL, May 11, 2017.

  1. M0XDL

    M0XDL New Member

    I recently sent the email below to:-

    AROS & IW COordinator

    On 04/05/2017 15:50, Ray Coles wrote:

    Good afternoon,

    I have finally got around to reporting a bizarre issue I always encounter when I work JT65 mode on 10.138 MHz (30m band).
    I listen to the band and copy a few (usually European) stations.
    I might then decide to call CQ or reply to a station.

    At the exact end of my transmission (or possibly before when I wouldn’t hear it) a strong modulated carrier kicks in, apparently automatically.

    This carrier and its 1 KHz or so tone makes listening very uncomfortable, but it doesn’t necessarily prevent JT65 replies being received.

    If I am alone on the band the carrier will stop (apparently automatically after a delay), but if there are other fairly strong stations it may continue, presumably continuously triggered by them.

    So, if there is a lot of band activity it just looks like a permanent interfering tone, but if I am alone or seeing only weaker stations on the band it quite obviously is triggered by my transmission.

    This only occurs on 30m, but I do see it on both my Elecraft K3 and my iCom 7300. My antenna is currently a full size G5RV but was also evident when I was using a BuckMaster OCFD.

    I usually transmit around 25W but turning the power down to 10W makes no difference.

    I believe it must be an automatic jammer because it is always “On duty”.

    I have tried to remember when it started but I have no proper recollection. At least 6 months I’d say.

    30M is a very useful band as we approach Solar Minimum, and this jammer takes a lot of the pleasure away.

    I don’t know if it is triggered by other modes like PSK or CW.

    Is it me?


    G0MGX replied that he thought it was something known to the EMC forum and suggested I join and post. So here I am!
  2. Ken G3SDW

    Ken G3SDW Moderator

    Hi Ray, thanks for posting on the forum with your problem.

    With out a doubt you have a VDSL (Super Fast Broadband) problem.

    You symptoms are classic of a local VDSL cabinet still in its training mode.

    There must be one very close to you as you say that even on very low power you can trigger it.

    Do you use VDSL by any chance, if so i suggest that you power down your house and do some tests on battery power first.

    If the problem persists after doing that then i will suggest that you get in touch with John Rogers M0JAV who looks after VDSL problems and he can arrange to have a remote test done on local phone lines to check for an unbalanced connection, this is normally the reason for a problem such as yours.

    You can contact him on m0jav@rsgb.org.uk


    EMC Help Desk
  3. M0XDL

    M0XDL New Member

  4. M0XDL

    M0XDL New Member

    Hi Ken,
    Strangely perhaps, I was delighted with your response!
    I hated thinking that there were UK amateurs mean spirited enough to jam my legal transmissions on 30m.
    Your VDSL alternative had the ring of a novel, surprising, but very plausible explanation!

    Yes, BT infinity arrived about a year ago and the cabinet is about 10 metres from my house! Furthermore, the copper to my house passes within about 2metres of my G5RV.

    Sorry to say I didn't understand your suggestion of powering down the house to confirm it (I think I am already convinced!).

    Perhaps you meant unpower my Infinity box, which seems a reasonable next step if it's that box which can cause the problem.

    It sounds as though the problem could be in the street cabinet or on other lines though.

    I'll await your response before contacting M0JAV!

  5. Ken G3SDW

    Ken G3SDW Moderator

    Assuming that you have VDSL then it could be you giving the problem via you phone line.
    So by powering down your house will prove it.
    If when you do unplug your broadband router your problem stays then that is the time to contact M0JAV
    Hope that makes things a bit clearer.
  6. M0XDL

    M0XDL New Member

    Well, I tried switching off and unplugging my Infinity router but the problem persisted.
    Time to contact M0JAV?
  7. Ken G3SDW

    Ken G3SDW Moderator

    Yes time is right Ray

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