Forums Music Sound Engineering EU : Potential interference source to wireless mics, 864.300 MHz

This topic contains 1 reply, has 1 voice, and was last updated by Avatar General Lighting May 29, 2014 at 10:45 am.

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    last night I received this odd signal (it is normal to hear wireless headphones and other such equipment around these frequencies, and this one is widely allocated for wireless microphones. Such devices are permitted throughout Europe without a special license from the Communications Ministry. They use analogue wideband FM transmission.

    However, this license seems to permit other devices than wireless mics.

    The signal was present for most of last night (the device producing it is currently switched off); As well as the data bursts I later on monitored (and recorded) what appears to be a combination of data, low frequency constant audio tones (often used on communications radios to identify a signal on a shared channel), on top of which was wideband audio that sounded like a microphone placed in a room. For privacy reasons I won’t upload that, but I will go through it as some point to see if I can identify the tones and maybe what device it could be.

    it might be a baby monitor; or a burglar alarm, but why put it on this frequency? There are others nearby that are still within the range that do not need licenses, and would not interfere with the microphones. I don’t think its owners are even aware of the interference they might cause, nor the risk to their privacy and security.

    The only info I could find about the exact use of the allocation was on Denmark Communications Ministry which had this subnote when used for alarms

    Note 4)

    Ingen andre analoge audioapplikationer end tale. Ingen analoge videoapplikationer

    which I think means “no other analogue audio than voice, no analogue video” (so the modulated data is against the license conditions at least there). The whole thing also hogs a lot of a channel when it could be done in a lot less bandwidth.

    If it carries on I may well have a chat with one of my neighbours (an older Chinese dude who has about 3 sat dishes in his garden and used to work at the telecom research (he was proudly wearing his old BT uniform jacket in the local shops) – I get the impression he might know a bit about wireless communications; plus he has children and grandchildren and would be better at explaining the risks and would not be as potentially intimidating (for some reason I seem to scare people way bigger than me when I don’t even intend to) – and then it is time for a bit of the old style tally-ho :wink:, the equipment is going to be in the same area as both of us as it does not have much output power. (I expect the owners of it will soon shut it off and the word on the estate will be “the Chinese feds tracked us!”)

    https://www.youtube.com/watch?v=0YbZqjmifUY

    tally ho… (been looking for this track for years, even more amusing given my ancestry that it turns out to be made by Indians but from a movie called China Town and played in a “chinese style”)

    #1278056

    I did a bit more monitoring and investigated the audio file; the low audio frequencies are 70 and 100 Hz. These are in a pattern not unlike MSF or the Soviet clock signal but do not appear to be on the exact second (which a clock signal would normally be, using the two different frequencies as binary code to set the time). The FSK data I haven’t decoded yet, but it is similar in appearance to the Motorola Flex pager signal but at a faster bit rate. (possibly 64 000 kbps).

    The FSK data only appears at certain times, I think it is a house burglar alarm that would be armed at night. I hope it isn’t a baby alarm, as that would mean the family have RFID-tagged the baby, and the equipment is sending pulses of UHF radio waves to it :crazy:

    And if the kit is smart enough to transmit 64kbps data (which isn’t trivial), why not encrypt the voice or at least invert the frequencies to make it more secure? It is probably American design, they think that us Europeans make the ETSI and ERO regulations for fun or to keep civil servants in work, and because no one has analogue TV any more they can get away with this. in reality they are why your gadgets normally work well in the whole of Europe and do not cause interference to others. License exempt doesn’t mean you can take the piss and sell defect equipment.

    I can easily see why Copenhagen would banish these devices; in those housing communes it seems that running cable across your own flat may be discouraged or forbidden; and equally likely that someone else works at somewhere like TC Lund and she has been allowed to borrow an 863 MHz wireless microphone to test for a performance at the weekend. Maybe they have the communal space still like the “great hall”, and she has tried to use this for the PA system for an evening house meeting, and the moment the receiver is turned on all this noise from the alarm gets blasted to every loudspeaker in the room; thus the owner of this bad equipment sheepishly removes it and gets a 433 or 868 MHz alarm instead (these are just as good and cause less problems) – and the next container load of these alarms from China is refused. And the whole lot probably all ends up in England 😥

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