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Radio Microphone Frequency confusion


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Good afternoon,

I Recently visited a school that had bought a 4-channel "Debra" beltpack radio mic system. They use the frequencies 501/511.5/524/538.5Mhz. According to some digging this frequency band is used for Maritime mobile and Aeronautical navigation (Radio Beacons). The Ofcom website says that SRD (Short range Devices) can be used in this band (ir2030). These devices have be be low power, although I can't find a reference to how low power. Someone did say that they fall under PMR (Personal Mobile Radio).

The questions are

Can they be used legally in the UK?

As they fall out of the PMSE allocated frequencies, would four spot frequency  licences be needed?

Thank you in advance


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That's a very odd system and if we had anything like a functioning trading standards system it wouldn't be for sale.

PMR is in 446MHz, so they wouldn't fall under PMR.
PMSE might issue a spot frequency license, but you'd need to ask. We have some spot frequencies in the 500MHz band at work. I think they probably cost similar to the purchase cost of the unit you link to, which is nearly always the result of buying cheap gear - it costs more to run.

Do you know that they actually run on those frequencies, or are you trusting the labelling on a bit of kit already known to be of somewhat suspect origin? I have a cheap(ish) spectrum analyser that is handy for this sort of thing.

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Hi Jon.

Yes, definitely transmitting on those frequencies. I carry a small hand held scanner. I didn’t see the “MPT” type approval number on the transmitter packs. Amazon sell a set “A” and a set “B” the school bought two set “A” and wondered why they were getting interference. 


Ps on another note, when did you get rid of the Midas XL4?…

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The XL4 left last year, to a good home wanting to refurb it and feed it multitracks on occasion. Still got plenty of other old stuff kicking about, but the XL4 was taking up a lot more space than we could justify. We did power it up one last time before it departed, having located 6 sturdy crew to be able to lift it and tip it. It told us to call Midas service dept - we were rather tempted to!

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Well for a start 511.5MHz is a satellite downlink frequency and looking at the Chinglish language in the instruction manual (and other clones of the system from Aliexpress at $99 for 4 channel rx, 4 hand mics, 4 body packs and mics) I understand your hesitation

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  • 2 weeks later...

Looks like those systems use what are effectively UK TV Channels 24 all the way up to 30. Most places around the UK they will be used for repeater TV stations if not for the main transmitters like Winter Hill and Sutton Coldfield. You could interfere with TV reception close to where you use them and on the other hand get interfered with if there is a TV repeater nearby. (Apart from it being illegal if you dont have a site licence).

Incredibly wasteful in terms of radio bandwidth. The Sennheiser A band which is in that frequency area can fit several dozen channels into that bandwidth. Not sure you would even be allowed to get a site licence for a device that used 6 TV bands just to get 4 audio signals across a room!


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Just copied from Canford website:


The frequency range 470 – 790 MHz is used for UK television broadcasting - but can also be assigned for radio microphones where they do not cause interference to television reception or are liable to suffer interference from television transmissions. The pattern of television coverage however is complex and constantly changing so contact Arqiva PMSE to determine whether given frequencies are available to be licensed at a particular location.

Licence fees for co-ordinated frequencies

£8.50 per frequency per 48 hour period – using the PMSE Licensing on-line application facility. (Or book direct with PMSE Licensing in writing – N.B. Then a minimum charge of £28 applies).

Long term (up to 1 year) annual charge available for indoor fixed sites only: £28 per frequency or £168 per UHF channel block.

Contact details

PMSE Licensing
2nd Floor Riverside House
2a Southwark Bridge Road

Tel: 020 7981 3803
Email: pmse@ofcom.org.uk
Web: Ofcom - PMSE Licensing

Obviously a good idea to check with PMSE to confirm.

All the best...


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Channels 24, 26, 27 and 29. That's a wide spread!

We operate channels 28, 29 and 31 here on a co-ordinated site license through Ofcom - paying the £168 per year per channel. I guess £28 per frequency is £112 per year, a bit better but hope no-one else in the area is using one of those TV channels (at a guess - they will be!)

Probably cheaper (and easier) if they returned it and just bought some Channel 38 kit.

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51 minutes ago, Simon Lewis said:

It's quite possible that the school doesn't have any radio mic licences and if asked will say "nobody told us..."

I bet that's the case for many users, be it schools, amdram etc. I've spoken to people who had no idea you sometimes needed licenses for wireless mics, and to be honest why would they if no-one told them or it wasn't right in front of them? It's similar with consumer drones. Sadly there are also some people who dive in and invest in systems without doing their homework or just get duff advice.

Maybe there should clearer labeling on equipment to boldly state that it may need a licence, on occasions when there is, it can be tucked away in the fine print or a really small font on a label.

Edited by sleah
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