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The SOS Guide To Going Live

Room To Roam

Radio Microphones

Radio mics free the vocalist from the restrictions imposed by cables - David Mellor presents a beginners' guide to the subject.


The one thing that has held back more potential superstars over the years than anything else is the cable at the end of the microphone, tying their aspirations to earth very firmly indeed. Cables and their connectors, in my experience, cause at least 95% of all sound system faults. One day science and technology will find a better way, but until then we shall all have to learn to make do and not get in too much of a tangle.

There is of course one very attractive alternative to the old fashioned 'string and chewing gum' approach to getting the signal from mic to mixer, and that is radio transmission. As we shall see, the term 'radio mic' covers a whole set of equipment, rather than just the mic itself, but let's dive right in to the essential do's and don'ts of radio mic trickery and find out what type of equipment you're likely to need to set your performance free.

WHO'S AFRAID OF THE DTI?



The first "do" of radio mics is to get one, if you are a vocal performer (or even a guitarist) who likes to show off on stage. Although top of the range radio mics are pretty expensive, there are lower cost models which compare very favourably in price to a quality guitar (plus amp) or keyboard. The first "don't" is don't be afraid of DTI (Department of Trade and Industry) regulations, unless you are actually manufacturing or selling radio mics. As a user, if you are using a low power transmitter then you don't need a licence; just fire the thing up and broadcast to your audience over the PA.

If radio mics have one problem it is that you can expect reception problems. There is always the risk that a signal from an outside transmission will get to your aerial first, and then your paying audience will be treated to a performance by the local taxi company's vocal ensemble. Fortunately, this doesn't happen often enough to cause significant annoyance. Rock audiences tend to have a tolerance for technical faults which West End theatre audiences don't (as in the infamous occasion when a prestigious musical was blown out by nearby radio mic transmissions from a well known broadcasting company). Improvements in frequency allocation in the last few years have helped, but regular radio mic users will confirm that more help is necessary.

HOW PRO CAN YOU GO?



There are two approved standards for radio mics, basically semi-pro and fully-pro, for want of a better description. The 'semi-pro' type, for which a licence isn't necessary, must conform to the DTI's standard MPT1345, which means that the transmitter must have been type approved and a sticker firmly affixed. An MPT1345 mic must have a power of less than 2mW and conform to certain other standards. The 'pro' transmitters, which do require a user licence, conform to MPT1350 and may have a power of 10mW for a handheld unit or 50mW for a bodypack transmitter. There are a total of five channels available for semi-pro mics in the VHF waveband, although there may be difficulties in using a mic working on the 174.8MHz channel in the same area as mics on either the 174.5 or 175MHz channels, bringing the effective maximum number of semi-pro radio mics on any one site down to four.

'Pro' mics, operating on UHF, need special licences, and in London may be operated effectively on as many as 21 channels simultaneously. There are fewer channels out in the provinces and fewer still close to specified radar installations. The restriction on channels is all due to the fact that everyone who wants to use the airwaves has to fit in with everyone else, including radio stations, police, ambulances, taxis and motorbike couriers etc. I could ask a very relevant question concerning how many radio mic users, apart from those with fixed installations, have a proper licence for their MPT1350 transmitter, but I won't...

Beyer Dynamic's NC170 true diversity receiver, with a handheld mic/transmitter.

So when you go to your local radio mic shop, what should you ask for and what should you expect to get for your money? Basically you need three items: a microphone; a transmitter; and a receiver. The term 'radio mic' covers all this paraphernalia. If you're a vocalist, then the chances are that you have an opinion on who makes good vocal mic anyway, so why not opt for a mic from a reputable manufacturer which has had a radio transmitter added? The Beyer hardware pictured here is just such a system, with a regular mic head attached to a larger than normal body which houses the transmitter. The receiver has two antennae which can be removed for optimal placing and operates in diversity mode.

DIVERSITY EXPLAINED



Diversity, in a radio receiver, means that there is more than one antenna and the receiver switches between them according to which is picking up the strongest signal from moment to moment. Believe me, this is a near-essential feature. In any building, especially where there is a steel supporting structure, there are complex patterns of reflections of the radio waves which can cause extremely troublesome 'dead zones' on stage. A diversity receiver almost eliminates this problem. The antennae should preferably be mounted as close to the transmitter as possible in a direct line of sight, for best results.

Guitarists can benefit from radio systems too, with instrument transmitters. Typically such a unit would be a small box, which can be strapped to a convenient part of your anatomy, with a flying jack lead that plugs straight into your guitar. The input circuitry is high impedance so the tone of your pick-ups should be unaffected.

THE COST



How much does a decent radio mic system cost? Well, I would advise researching radio mics thoroughly rather than necessarily going for the first one you heard about, but as I said earlier, it compares well with the price of a decent synth, although it may still come as a shock to the band's vocalist who hasn't up until now been used to spending real money on his or her personal equipment. Manufacturers with DTI-approved products to offer include Beyer Dynamic, Sennheiser (their Mikroport series is particularly well respected), Micron (British made!), HW International, and Trantec.


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Control Zones


Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.

 

Sound On Sound - Mar 1992

The SOS Guide To Going Live

Feature by David Mellor

Previous article in this issue:

> Say It Loud!

Next article in this issue:

> Control Zones


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