Radiomicrophones / Wireless Microphones

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Introduction
You may be a little bewildered by the range of prices and types of radiomicrophones, so here's a short introduction followed by the technicalities

The quality and price of radiomicrophones ranges from entry level home disco and 'karaoke' types costing £80 or less right up to thousands of pounds for broadcast quality products.  The main differences will be in transmission range, reliability of the radio (RF) link, robustness of the hardware, and the audio / sound quality.  With the cheapest, don't expect more than about 20 metres of range - any more, and you'll get gaps, or drop-outs, in the coverage, which may at worst give you a brief 'shhhtt' noise rather than silence

More expensive, and you'll get a 'diversity' receiver with your radiomicrophone.  Diversity means two separate receivers in one box, with two separate receiving antennas or aerials.  The receiver that's getting the better signal is selected automatically -- so there's a good chance that if one receiver sees a gap in coverage, the other one is still working well.  (But watch out -- some cheaper receiver boxes have two antennas but are not  diversity)

There are three different types of radiomicrophone transmitter:

Hand-held transmitters have the microphone and transmitter in the same microphone casing
Add-on transmitters fit on to standard microphones, making them into hand-held radiomicrophones
Bodyworn beltpack transmitters allow clothing clip microphones, headworn microphones (headmics) and guitars etc. to connect to a separate radiomicrophone transmitter that is worn on a belt or in a pocket

There are two legal radio bands in the UK that don't require a licence for use – these are called de-regulated frequencies. The older VHF one is between 173.8 and 175.0 MHz (megahertz) - this is often termed ‘legacy frequency’ and the newer UHF one is between 863.0 and 865.0 MHz.  The UHF one is a pan-European allocation, but note that other European countries also allocate other bands, so don't assume that a radiomicrophone bought in Europe is legal to use in the UK

Manufacturers label the frequency of their radiomicrophones on the equipment and sales literature etc.  Naturally, if you are going to use more than one, each needs to have its own frequency.  Some radiomicrophones allow the user to select from a range of frequencies. Do not assume that you will be able to use all frequencies, as intermodulation distortion and interference are common problems – often it is best to have at least 350 kHz between the frequencies you are using – 500 kHz between the  frequencies is even better

Radiomicrophones all need a battery.  Some designs use a PP3 9V battery, and operate for a time between 3 and 8 hours from an alkaline battery.  Newer types often use a pair of AA or AAA cells and last for 5 to 10 hours. Be aware that the when the battery in a radiomicrophone transmitter gets low on voltage (around 8.2v for a PP3, for instance) the radiomicrophone audio signal (your voice) will often be muted by the radiomicrophone receiver

VHF or UHF?
In 2011 we tend to use UHF radiomicrophones rather than VHF radiomicrophones

UHF (Ultra High Frequency) radiomicrophones operate between 606 MHz and 870 MHz whilst VHF (Very High Frequency) types  operate between 173 MHz and 220 MHz. Manufactures are tending to put less effort into VHF systems and all but entry level systems will be using UHF

If you are using VHF systems use frequencies 173.800 to 175.000 MHz  as they are license exempt / de-regulated and can be used free of charge in the UK. Please be aware that 174.800 tends to have intermodulation problems and if you need to use frequencies other than these you will need a license from JFMG - see chart

Radiomicrophones or In-Ear Monitoring (IEM)?
Please note that although this page is about radiomicrophones the concepts apply equally to In-Ear Monitoring (IEM) systems too – as these use the same UHF.  So, when you’re thinking about how many channels and licences you need for your radio equipment don’t just count your radiomicrophones consider your In-Ear Monitors as well

UHF Frequency and Channels
When radio frequencies are talked about, they are often referred by their channel number such as “channel 69”
Here is a simple list describing the channels that are often used for radiomicrophones in the UK:

Channel 38 - 606 to 614 MHz - Shared with television also used for talkback systems as well as radiomicrophones      
Channel 69 - 854 to 862 MHz - Radio Microphones and other point to point audio links      
Channel 70 - 863 to 865 MHz - De-regulated / License Exempt Radio Microphones

Example Sets of Ch 70 Usable UHF Frequencies
Here are example sets of 4 usable frequencies in the de-regulated band (Ch 70) that have been tested for (their lack of) intermodulation:
 
Mic 1    863.250 MHz      
Mic 2    863.750 MHz      
Mic 3    864.625 MHz      
Mic 4    864.990 MHz     
 or
Mic 1    863.100 MHz      
Mic 2    863.900 MHz      
Mic 3    864.500 MHz      
Mic 4    864.900 MHz 

However Sennheiser recommend the following 4 frequencies:
Mic 1    863.100 MHz      
Mic 2    863.500 MHz      
Mic 3    864.300 MHz      
Mic 4    864.900 MHz 

If you need to use more than 4 radiomicrophones then you currently have just two choices - purchase a license from JFMG and use Ch 38 or purchase Sennheiser G3 radiomicrophone systems that can operate a maximum of 6 channels / systems at the same time in Ch 70

Channel 38 Changeover
It is a fairly complex subject, however we will attempt to provide you with the key information

As a result of the switchover from analogue to digital TV transmission and the consequential reduction of frequency spectrum required, the government is to release (sell off) some radio spectrum for other purposes. This includes frequencies currently being used by many radiomicrophone and In-Ear Monitoring (IEM) systems. TV Channel 69 (854 to 862 MHz) is currently designated for radiomicrophones. A great many wireless products previously sold in the UK operate on Ch 69

Radiomicrophones are the primary user for this part of spectrum, meaning they have the priority on this spectrum's use

Most products operating on Ch 69 also have access to some deregulated spectrum in TV channel 70. This narrow slice of spectrum runs from 863 to 865 MHz and will not be affected by the Digital Switch Over. Only a small number of wireless systems can be used simultaneously in Ch 70, and this depends upon the technical specification of the radiomicrophone being used - typically a maximum of 4 systems can be used at the same time

Frequencies within Ch 70 - 863 to 865 MHz are the only part of the UHF spectrum that can be used without holding a licence

Licensed users will have access to Ch 69 until at least July 1st 2012, after which, it will be phased out completely

Ch 38 has been named as the only direct replacement to Ch 69. Radio astronomy, which currently holds the licence to Ch 38, will be phased out of this band. As Ch 38 - 606.00 to 614.00MHz is now available nationwide and temporary access to Ch 39 & 40 has been granted. However, post 2012, Ch 38 will be the only shared channel available to radiomicrophone users

Purchasing Licenses
You can purchase a license from JFMG to use frequencies. As of 2010 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 outside of Ch 70, then you are committing an offence under the Wireless Telegraphy Act - click here to download a JFMG radiomic licence application form
Get more info from www.jfmg.co.uk

Changes to Radiomicrophone Frequencies - The Facts
There has been much publicity concerning the changes which are being made to the frequency spectrum allocation at Government level, and the extent to which these changes will impact the use of radiomicrophones in the UK

Some of the internet campaigns have been scary, and the perceived threats exaggerated, but it will impact some users so let’s establish some facts

OfCom are conducting a review of the available UHF frequencies and will auction off TV Ch 31 to 37 and Ch 61 to 69 probably for the growing use of mobile broadband

The vast majority of UK users will be “community users” operating the de-regulated frequencies and will be unaffected by the change. That is anyone using Ch 70 - 863 to 865 MHz will not need to change

In any event, the changeover is not programmed to take effect until after the Olympics and probably at the end of 2012, so there is no immediate threat

Other radiomicrophone users will be more seriously impacted called PMSE (programme makers like the BBC and West End Theatres etc.) This body is represented by BIERG who are representing the users in talks with Government

Radiomicrophones (and wireless In-Ear-Monitors) currently use:
    Ch 70 UHF frequencies 863 to 865 MHz are de-regulated - these do not and will not need a license in the UK or EU
    Ch 69 UHF frequencies 854 to 862 MHz  are regulated and need a license in the UK and will not be available by the end of  
        2012 - users will have to change to Ch 38 - 606 to 614 MHz

For those users using de-regulated frequencies for less than four radiomicrophones there will be no requirement to change

Only those users with multiple radiomicrophones, or using radiomicrophones in the vicinity of other users and as such have other frequencies licensed to them will be affected by the change and will need to replace their equipment

If you come into this category (which is usually Ch 69 - 854 to 862 MHz) provision has been made for Ch 38 - 606 to 614 MHz to be available for radiomicrophone licensing together with some interim frequencies in Ch 39 and Ch 40

Affected users will need to change frequencies. Some high end systems including Shure models SLX, ULX and UHF-R and Sennheiser G3 and 2000 series are adaptable to the new Ch 38 allocation. Other systems will not be able to re-tuned and these models will have to be replaced at the owners cost

It is likely that some manufacturers will offer a kind of “trade in” to ease the burden of the cost of change

Any new users who need licensable frequencies will be advised by their supplier to purchase only systems compatible with the proposed frequency allocation on Ch 38

Many users will still have older VHF radiomicrophones and can continue to use these (170 to 210 MHz) after the TV Digital switch over (DSO) although they may choose to take this opportunity to upgrade to new UHF equipment

Do I need a Radiomicrophone License?
Not if you are operating less than four radiomicrophones on the de-regulated frequencies between on Ch 70 - 863 to 865 MHz

By law you will need be in possession of a license to legally operate radiomicrophones if you are using Ch  69 - 854 to 862 MHz now and change to Ch 38 - 606 to 614 MHz in 2012. Ch 69 will become illegal for radiomicrophone use during 2012

Get more info from www.jfmg.co.uk

Frequently Asked Questions
Q - What is the difference between Single channel, Diversity and True Diversity?
A - Single channel receivers have one antenna and one receiver circuit. Diversity receivers have two antennae and a circuit, which selects the strongest aerial signal. True Diversity receivers have two aerials and two totally independent RF receiver modules and a circuit, which selects the best channel for both signal strength and signal-to-noise ratio

Q - How many transmitters can I use with my radiomicrophone receiver?
A - Only one. Two transmitters operating on the same frequency will interfere with each other. It is possible to have both a handheld and guitar or clothing-clip mic transmitter on the same frequency, and use them with the same receiver, but not at the same time

Q - How far from the receiver can I place my antenna?
A - As long as you use 50 Ohm fully screened RG58 aerial cable up to ten metres, but the closer the better. It is possible, by employing antenna amplifiers to run longer cables

Q - Can I use my handheld radiomicrophone and receiver from different manufacturers if they are on the same frequency?
A - Possibly yes, but careful attention must be paid to specifications, because different makes and models have different technical parameters for equalisation, compression and expansion. Sometimes there are even compatibility issues between different models from the same manufacturer. It would be prudent not to assume compatibility between different manufacturers, unless tried and tested first

Q - Is there a performance difference between UHF and VHF?
A – No - there is little audible performance difference but, with the high demand for a greater number of usable, interference free frequencies, the UHF band offers more opportunities – however the VHF band can often transmit a longer distance without dropouts

Q - What is a compressor, expander or compander?
A – The audio signal is compressed (squashed) before being transmitted and the radiomicrophone receiver expands the signal back to its original state, thereby improving the signal-to-noise ratio

Q - What is FM Modulation?
A - FM is the abbreviation for Frequency Modulation, which is the method of transmitting information by modulating a carrier frequency on a radio transmitter. The frequency of the carrier wave is varied in accordance with the amplitude of the input signal, while the amplitude of the carrier remains unchanged

Q - What is the difference between Squelch and Mute on different radiomicrophone receivers?
A – Nothing. A squelch circuit mutes the output of a receiver when the received signal falls too low for good reception. Some units have preset mute levels while others have manual settings. It should be set so that the receiver mutes when the transmitter is switched off, or goes out of range, before the signal is swamped with noise or interference. To achieve a good setting, turn the transmitter off - Set the squelch control to minimum and then turn it up until noise starts to disappear. A good, tried and tested position for mute/squelch controls is around a quarter turn from the fully anticlockwise position

Links to pages and documents relating to Radiomicrophones and their UK frequencies

Sound Advice - Sound Services Guide to Radiomicrophones in the UK
Sound Advice - Sound Services Guide to Radiomicrophone Basics
Sound Advice - Shure Guide to Radiomicrophones
Sound Advice - Audio-Technica Guide to Church Microphones
Sound Advice - Audio-Technica Guide to Microphones

Get more info from www.jfmg.co.uk

UHF Frequencies used by various manufacturers
Audio Intimidation
Audio-Technica
Audio-Technica - EU only
Chiayo
Citronic
Gemini 16ch - UK
Gemini 16ch - USA
Gemini 64ch - UK
IMG Stageline - 600 Series inc. TXS-611, TXS-616, TXS-631 & TXS-616 etc.
IMG Stageline - 800 Series inc. TXS-810, TXS830, TXS-840, TXS-870, TXS-880, TXS890 etc.
JTS
KAM
Samson
Sennheiser - Ch 69 & 70
Toa
Trantec

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