FT8 transmissions on 80m and 40m causing house alarm activation to neighbour

Discussion in 'Interference Problems' started by M6OLT, Oct 23, 2017.

  1. M6OLT

    M6OLT New Member

    My next door neighbour has just been around to advise that between certain times last night, the internal alarm sounder on his alarm box went off 3-4 times. Having checked in my log at these times I was operating FT8 @ 10w on 80mtrs and also 40mtrs.

    This seems to have happened on a couple of instances over the last week. I intend to test tonight between agreed hours to determine if this alarm interaction is the cause. Has anyone else experienced such issues and if so, what advice do you have.

    Thanks in advance.
    Adam (M6OLT)
  2. gm3sek

    gm3sek New Member

    Hi Adam

    If you do prove to be triggering next-door's alarm, you need to tell us a LOT more. Any of the following might provide a clue.
    • What type of antenna are you using? (dipole, end-fed etc)
    • Indoors or outdoors?
    • What kind of feedline?
    • Do you use any kind of "RF earth" connection? (I'm not implying that you necessarily should.)
    • How far away is the nearest point of yoru antenna from next-door's alarm wiring?
    Also, what do you know about his alarm system?

    Could be many more questions, but our mains just dropped out! Quick, before the UPS dies...

    73 from Ian GM3SEK
  3. Ken G3SDW

    Ken G3SDW Moderator

    Sensible questions Ian, thank you for coming in.
  4. M6OLT

    M6OLT New Member

    I performed a half hour FT8 test last night between 20:19 and 20:49 on 80mtrs (3.57224)with power set at 10w and sending out a CQ. I had 7 QSO's with other European stations during this time frame and the upon checking with my neighbour, there was no activation of his control panel speaker. I will test again this evening on 40mtrs for a similar time period to see what happens.

    The antenna is a home brew random length antenna which is fed by a 50ohm coaxial cable running along the base of my garden fence up into my first floor shack. It has 2 x 16mm earth cables connected to a 4ft copper earth rod installed at the base of a CG-3000 Tuner to which it is coupled. There are also 2x 1.5mm ground elements which follow the fence line for 15 mtrs in one direction and 10 mtrs in another direction. The antenna wire connects to the top wingnut of the CG-2000 and is spiral wound loosely vertically around a 10mtr extendable (roach type) pole. The wire then transforms to a horizontal where it is suspended in the air for another 10 mtrs at a 90 degree angle to another 10mtr pole where it finally turns another 90 degrees and is suspended for another 7 metres before terminating on a dog bone insulator off of 2 mtrs of paracord which is terminated to the brick work of the house just below the roof boards.

    My neighbour's alarm system is an Castle Care-tech Euro Mini (i believe this to be a wired system) and the user manual shows as follows.


    I shall perform testing again this evening on another band to see if I can trigger the alarm.

    Kind regards
    Adam (M6OLT)
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  5. M6OLT

    M6OLT New Member

    Distance from the closest point of the feeder to the neighbour is approximately 10 feet at 8ft height from the ground. The closest point of the radiating wire is about 30ft at a height of 1 mtr.
    gm3sek likes this.
  6. Ken G3SDW

    Ken G3SDW Moderator

    Thanks for those details Adam, just to get things straight, the tuner is at the base of the antenna, is that correct?
  7. M6OLT

    M6OLT New Member

    Yes, the tuner at the base of the antenna fixed to my fence at about 8 inches above the floor.
  8. M6OLT

    M6OLT New Member

  9. M6OLT

    M6OLT New Member


    Attached Files:

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  10. Ken G3SDW

    Ken G3SDW Moderator

    Thats great Adam, in fact i have exactly the same antenna here, only difference is that i feed the base of the antenna with a 9:1 unun, and works extremely well considering it is a compromise.
    M6OLT likes this.

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