Silent Key

I have a problem. Actually car owners in my neighborhood have a problem. While doing some tests with an Echolink node on 70cm, one of the neighbors came by and asked if I could have a look at his car key. He owns one of those fancy new cars which don’t use old fashioned keys anymore, and he wasn’t able to open his car. Nothing new, I wrote about this before.


It seems that these state-of-the-art systems rely on 433 MHz too. My 5 Watt signal transmits at least 2 MHz below that frequency, but this incident makes it clear that the receivers in these cars aren’t very picky. Technically it is not my problem – the band’s primary use is ham radio, any other use is at someones own risk. I prefer not to think in black & white though, but I have no idea how to fix this.

12 comments on “Silent Key

  1. This story reminds me of my father in law who couldn’t get his car started; when I switched off my FT-8900 which I was using as a crossband repeater from PI3AMF to a frequency in the 70cm band it worked again…. after the Wegenwacht had a look at the car as well. I never told them the real cause, hi!

  2. Same problem here in Germany with the “new” 868 MHZ Devices… (used in Bosch Keys, all home automatisation etc.)
    As T-Mobile Germany has their 800 MHZ LTE Channel at 862 MHZ (Uplink) all this devices not working when you have a LTE Device transmitting in the neighborhood transmitting. 868 MHZ Receiver must be superhet receiver to solve this problem…


  3. Yes, but we as operators still have a duty of non interference. Even though you are operating on an appropriate frequency I be leave you must stop if your transmissions cause issues. Just as if your transmissions cause interference with TVs or radios. Or am I wrong?


    • Yes, you’re wrong. We don’t interfere, these gadgets do. We would have to quit our hobby for every (non EMC compliant) crappy touch light, weather station, door opener, doorbell and who-knows-what gadget they think of lately. Manufacturers of car keys have a choice (868MHz for example), we don’t.

      Manufacturers of HiFi and TV have a choice too (confirm to EMC rules or not). Car manufacturers are well aware of the problem, yet they choose to continue our frequencies.

      We are NOT allowed to interfere on purpose. That’s why we avoid that specific frequency like the plague.

  4. i know that some wireless alarm systems work on 70cm as well…. could you jam it to break in?? hehehehehehe …..
    But as a suggestion to solve your problem, i wonder if you take a many element beam for 70cm…. the signal would be so directed to where you want it to go that possibly the cars will not have a problem anymore…..
    At least its something to test 🙂 , I’ll help ….

    As a reply to Wolfgang….
    If the manufacturer made a receiver only listening on the frequency the transmitter (read key) works on, and not 2Mhz (or more) wide then there would not be a problem.
    But this costs a bit of wire and a few coils, and maybe a few capacitors to make a bandwidth filter.. making the car a whooping 5 bucks (or less) more expensive to Build….. and as the money hungry, fat, obnoxious CEO’s want all the money they can have, this won’t ever happen. 🙂

    So i agree with Hans… we won’t stop our hobby just because they refuse to build a proper product 🙂

  5. I can only make one barely-useful comment. Many years ago I used to specialise in 2m SSB, and the only antenna I had in the air was a 2m Tonna yagi. My neighbour, two houses down the street, was directly in my line-of-fire for tropo lifts to the European mainland. Anyhow, one day this neighbour came round and politely mentioned that his TV was dancing and asked if I knew anything about it. I said yes, possibly he was getting breakthrough from me, and although my station was ‘clean’ and that was where my responsibility ended, I would gladly see what could be done to minimise the problem.

    Firstly I asked if there was any time he particularly watched TV, so that I could avoid those times. He said that he watched it from the time he got up in the morning until he went to bed. The problem was that he had had a massive heart attack and was virtually immobile, and the TV was his only pass-time. So that left us with filtering. One day, at a relatively convenient time for my neighbour, I called round with various filters and other devices. I was armed with a hand-held, and my dad was back at my house manning the 2m rig. At a given signal from me, dad transmitted. I tried ever single filter and nothing worked. So I took the TV aerial out and we tried again – the TV danced! I tried turning the TV set at right-angles to my station – the TV danced.

    My neighbour just happened to have one of those TVs with a receiver as wide as the door of the local bus depot! Well, he was a nice guy and I didn’t want to spoil his only pleasure, so I agreed to go QRT until I could find some other way of enjoying my hobby. That turned out to be expensive – I set up an antenna system for elliptical-orbiting satellites.

    Anyhow, the last thing I said to my neighbour after my attempts to cure his breakthrough, was a plea to him that if he ever replaced his TV, he would get a set on approval, and I would fire everything I had at it. If there was breakthrough he would send it back to the shop and try another one, until we found one that was compatible. Like I said, he was a decent guy.

    So basically, you could ask your neighbour that next time he wants a car with a radio-key, he should come round with a demonstrator model from the dealer, and you will try to blast all hell out of the radio key first. Like I said – not much of a solution.

  6. You say “the band’s primary use is ham radio”

    I believe 70cm is a shared band, secondary for amateurs (in the UK at least), with the military and ISM as primary users. The ISM band 433.05-434.79 is where these LPDs operate as licence-free devices. We have a duty not to cause wilful interference.

    Is it different in PD-land?

    • Only the 435-440 MHz part is secondary for ham radio, 430 – 435 MHz is primary. Any device operating there (LPD, weather stations, car keys, whatever) can’t complain to authorities when ham radio stations cause problems.

  7. I just had an opportunity to nip a problem in the making in the bud. We are working on a short range telemetry system for transmitting digital acquisition information to a central gathering point. One engineer suggested using the ISM channel at 433.920MHz. I showed him my new Baofeng transceiver and explained that if one of these DAQ systems happened to be installed within a few miles of an amateur repeater operating within a few MHz of the DAQ system it probably wouldn’t function. We’re going to pursue another ISM frequency that won’t suffer such problems.

  8. Yes supermrket car parks are not places to hold QSO’s on 70cms watch them all thumping 7 shades of phoontang out of the poor keyfob it can be rather amusing (but naughty)

  9. That sounds like a good time to me. But then I tend to be a little naughty.

    Back in the 70’s the microwave company I worked for moved and I decided to stay behind and sell their products. I had developed a line of microwave security equipment including a couple small motion detectors operating at 10.525GHz. One of them had a backup battery that would run the unit for a couple hours.

    I made a sales call in Cleveland and when I put my various units back in the car I forgot to disconnect the battery on one. I headed West on the Ohio turnpike and as was my practice I stuck it on 55mph, the speed limit at that time. I soon noticed that nobody was passing me. In addition to the transmitter I had call letter plates and a 19″ whip in the middle of the roof. Only a few had the nerve to pass me at 57mph. I tried to look very stern as they went by but it was difficult.

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