Radio Microphones – Legal and Usable Frequencies

Here in the UK, we need to be careful about what frequencies we set out radio microphone receivers/transmitters. Even if your radio mic set has 1,400  available frequencies only a few are usable legally without a license. Hopefully this page covers the basics and give some practical advise in using radio microphones.

VHF or UHF?

Firstly, this page is about UHF microphones rather than VHF microphones. UHF (Ultra High Frequency) radios operate between 822 MHz and 870 MHz whilst VHF (Very High Frequencies) operate between 173 MHz and 220 MHz. Manufactures are tending to put less effort in to VHF systems, and pretty much your baseline system (eg from Shure, Sennheiser etc) will be using UHF. Cheaper systems may be using VHF, do be careful when buying cheap systems, as you really do get what you pay for – at least purchasing the entry level systems from the top brands is a good place to start – eg Sennheiser G2 series…

If you are using VHF, then all I can say is that these frequencies: 173.80 MHz, 174.10 MHz, 174.50 MHz, 174.80 MHz, 175.00 MHz will be the ones to use, as they are license exempt and can be used free of charge. (be careful with 174.80 as it tends to have intermod problems. If you want to use frequencies other than these then you will need a license (more info about Intermod and licenses below)

Radio Mics or IEM?

Another thing to note, is that in this page I tend to talk about Radio Microphones, but the concepts apply to In Ear Monitoring systems too – as these use UHF. (IEM is where, rather than a ‘wedge’ speaker for the people up front, they have ear phones that are connected to a radio receiver, and they can monitor themselves that way). So, when your thinking about how many channels you need for your radio equipment, don’t just count your microphones, but count your in ear monitors too!

Radio Microphone Frequencies:

The  Sennheiser G2 series of microphones are fairly common in Churches – they are solid, reliable microphones that are in the professional bracket, all be it at the cheap end. A G2 can operate on 1,400 tunable frequencies, from 518MHz up to 866MHz – so how do you choose with frequency to use?

Frequency Channels:

When radio frequencies are talked about, they are often referred to as their channel number, eg "channel 69". Here is a simple table describing the channels that are often used for wireless microphones:

Data correct as of October 2009

As you can see, there are lots of frequencies, but apart from channel 70 all of them require a license.

Free frequencies:

Channel 70, 863 MHz to 864.99 MHz are license exempt. This frequencies can be used without a license – remember though that lots of your neighbours may well be using these same frequencies so watch out for picking up other people’s audio!

Purchasing Frequencies

You can purchase license to use frequencies. For about £75/year (or £135/2 years) you will be licensed to use up to 14 channels… The organisation that manages frequencies in the UK is JFMG. They will assign you frequencies to use that are specific for your area – this ensures that even if your neighbour purchases a license they will be given a separate set of frequencies and you won’t clash. If you use frequencies out side of Channel 70, then you are committing an offence under the Wireless Telegraphy Act! More info from http://www.jfmg.co.uk

Intermodulation

When multiple frequencies when used together, eg if you have more than one radio microphone, the frequencies can sometimes form additional frequencies that are outside the original ones used and cause problems – it’s best to avoid this and therefore pick your frequencies carefully. This is called intermodualtion, ot intermod for short! It’s worth noting that you can mix UHF and VHF systems without having them interfering with each other as there is a big enough gap between the UHF and VHF frequencies.

Intermodulation checkers:

There are software programs that you can purchase, however Audio Technica have a free online checker that is simple to use from their web page. Also, Sennheiser have a intermodulation software program that you can download: Sennheiser.

Unlicensed/Free Frequencies in the Future

As already said, channel 70 (863 -864.99MHz) is unlicensed and will be remaining so after 2012. The debate Ofcom are having at the moment is regarding Channel 69, and selling those ranges off… the question is, what happens to wireless microphones that are currently licensed to use Channel 69?

Example Sets of Usable Frequencies:

Here are 2 example sets of 4 usable frequencies in the free/unlicensed bands (channel 70) that have been tested for intermodulation:

If you are wanting to use more than 4 radio microphones then you have no choice apart from purchasing a license.

You would only use one of these groups – choose either the blue or the green group! – or find your own set of frequencies that don’t have an intermod problem.

Other Links:

This page is an amalgamation of other resources I have collected and compiled and tried to re-write in an easy to understand way, here are some other links to further your reading:

• A Discussion: http://www.worshipcentral.org/forum/topic/microphones?page=2
• Intermodulation: http://en.wikipedia.org/wiki/Intermodulation
• Channel 69 sell off comment by Sennheiser: http://www.theaudiofiles.net/2009/05/uhf-frequencies-what%E2%80%99s-happening/

Closing Notes

This information was compiled from various resources and is thought to be correct at the time of writing (October 2009) – this information doesn’t come with any guarantees, but do use it for informational purposes.

Please do leave a reply below with other information, feedback etc!

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