Killing Intercom Key Fobs?

Discussion in 'EMC Matters' started by MM0IMC, Nov 8, 2019.

  1. MM0IMC

    MM0IMC New Member

    A rather dramatic title, but I wonder if I'm killing my neighbour's RFID door entry key fobs with my station's RF?

    Randomly it seems, that the landlord (Council) have to come out and re-programme one of my neighbour's electronic key fobs to let them in. I run QRO, just below the legal limit and have had issues with RFI to the intercom system before (audio breakthrough on to the internal handsets). There's occasions where key fobs have just failed.

    I've been running QRO on and off for years. I thought if it was an RFI problem, that the key fobs would be affected more often. I've not kept a log of when the key fobs have gone wonky, so it may just be coincidental...

    It's a GDX system by Stanley.


    Ian - MM0IMC.
  2. Ken G3SDW

    Ken G3SDW Moderator

    You dont say what bands you normally operate, what antennas you use and there location in regard to the Stanley GDX system

    Just looking at the details of the system but cannot find out how they are designed but i am sure that the key fob must work on and around 70cm.

    I would not have thought that you and i take it you are talking about HF QRO would trouble a key fob at 70cm.

    Is it the same person having the problem or is it others as well.

    I cannot see how you are to blame unless you have excessive RF voltages floating around

    From what i have read they all have individual unit installed in each home but the front door unit communicates with each individually home via PLE, read this
    GDX by STANLEY Product & Technology has launched GDX7 – a Power Line Ethernet (PLE) system with a standard two-core cable for transmitting communications and power to each system component – in the UK.
  3. MM0IMC

    MM0IMC New Member

    Apologies for that, but I run an Inverted V dipole for 40m/20m, with the high voltage ends at about 7m away from the metal box housing the intercom motherboard, etc. If you like at my QRZ page, as you'd expect with an Inverted V dipole, the high voltage ends come down to near the ground and the centre is up about 20ft, with a large 'ugly' chock balun just below that, to try to restrict CMC.

    I thought that the key fobs worked with a large internal compact wire aerial, similar to the ones that shops use to deter thieves? Take a look at the brochure for the fobs and you'll see that they work on LF at 153kHz. Token.pdf
  4. Ken G3SDW

    Ken G3SDW Moderator

    Ok now i can see how it works, i still dont understand how your RF is killing there keys, you did not say if it is one or many others being affected.

    My only other comment is that using QRO in a locality such as yours, by the way i have looked at your page, as you leave your self wide open for possible problems such as this, i underline possible.

    Just giving this some thought and if it is you killing there fobs then when does that happen as the probability of it being you on the air when they come home to gain entry is rather unlikely

    Why do you need QRO, power is not everything, my opinion of course.
    Last edited: Nov 8, 2019
  5. MM0IMC

    MM0IMC New Member

    I live in a 4 in a block flat and there are usually 2 key fobs per household. With the increase noise levels on the bands that I use and not just at my end, but the receiving station, I tend to find QRO is sometimes the only way to make the contact. More so when you're up against the EU powerhouse stations! Beam aerials aren't an option here, unfortunately.

    I said killing the fobs rather erroneously, but I think it's more likely the intercom panel outside the front close door or the main board itself being affected by the RFI, if that makes sense?

    I use to use QRP with an FT-817ND when I was portable, so I'm not wholly a QRO'er... Your mileage will vary though...
  6. Ken G3SDW

    Ken G3SDW Moderator

    Will is it indeed!
    If it is you causing this problem you need to remember, and i have looked at you location on Google maps, and can see were your antenna`s are, assuming that is a communal area then be very careful as if the council get involved they may well insist that you take your antennas down, your fault or not, assuming you did not get permission in the first place.

    What SWR do you get without an ATU connected on either band, as from what i can see in your pictures then you have a 40m and a 20m antenna with a common feeder, nothing wrong with doing it that way but it is a compromise so dimensions have to be totally correct, how did you work that one out.

    Finally i see you use what is called an Ugly balun, fine and simple, have you not go a good current balun as they are by far the best as using QRO you must take every caution in the book living in close proximity as you do to many other dwellings.
  7. MM0IMC

    MM0IMC New Member

    The pole holding up the aerial and the wire elements themselves are on a private fence belonging to a bought house next door (with the neighbour's permission). The dimension were done with trial and error over the years, but around 2013 I believe, I got a RigExpert AA-54 antenna analyser that certainly helped! The VSWR is 1:1.1 on 14.185MHz, raising to 1:1.5 at the band edges of 20m. On 40m, it's a similar reading. It tends to rise a little due to ground reflections when we get a downpour, more so on 40m. It's sandy soil, so drains relatively quickly.

    I've fitted type 31 clip on ferrites to some of the internal wiring of the intercom motherboard, just in case. It was giving me problems from it's SMPS a number of years ago, but thankfully Ofcom came out and helped me sort that problem! That was affecting 60m reception and some of the higher bands...
  8. MM0IMC

    MM0IMC New Member

    I forgot to add that the dipole elements are linear loaded, with the ends folded back. This allows me to lengthen and shorten them equally, for tuning purposes, without having to cut wire off.
  9. Ken G3SDW

    Ken G3SDW Moderator

    Very good Ian, nice to see that you do things the correct way.

    Well at this stage all i can say is carry on regardless as it would appear that your station is in order.
  10. MM0IMC

    MM0IMC New Member

    Thanks, I do try to run a clean station. I try to take remedial action, when and where necessary.;)
  11. Ken G3SDW

    Ken G3SDW Moderator

    Thats a credit to you, and at the end of the day if those key fobs are being interfered with then they must be non complaint anyway,

    Good man

Share This Page