Online Guide Radio Mics

General Information

A radio or ‘wireless’ microphone, as its name suggests, does not require a cable to carry its audio signal to a mixer or other audio equipment. They’re designed to give the singer, speaker or instrumentalist the freedom to move about the stage unhindered, and are also widely used in electronic news gathering (ENG). Wireless systems comprise three basic components - microphone, transmitter and receiver. Wireless mics are either handheld, lavalier (also known as ‘tie-clip’ ), headset or instrument ‘clip-on’ models, each designed with specific applications in mind. Transmitters are usually either built into the body of the mic, or come as a separate belt-pack that the mic is connected to – they process the audio signal from the mic and send it out as a radio signal. The receiver then picks up this broadcast and converts it back into an audio signal.

Handheld Microphone with Built-in Transmitter

Belt Pack Transmitter

Plug-on Transmitter

Online Guide Radio Mics

Areas of Application

For each transmitter, you need a receiver that matches its radio frequency channel. Receivers can only lock onto one signal at a time, in the same way as you can only listen to one radio station at a time on your domestic radio! So if you want to use two radio mics simultaneously, then each will need its own receiver. The two systems must be on different channels so that their signals do not interfere with each other.

Online Guide Radio Mics

What Frequency?

Wireless mics operate within a specific band of radio frequencies which varies from country to country. This is to avoid interference with other devices which have different bands of the spectrum set aside for them, for instance television and radio networks, mobile phones and WiFi routers. Depending on the frequency bands they use, wireless systems are classified as either VHF (Very High Frequency) or UHF (Ultra High Frequency). UHF systems have higher output transmission power and so are less susceptible to interference – they can also carry higher bandwidth audio signals than VHF.

Any wireless system must conform to government regulations. As often as not, this will be a problem for the manufacturer to sort out, as the products you buy in any given country will likely conform out of the box. But with more sophisticated multiple wireless systems designed for international use, you may need to apply for a licence. Radio systems designed for sale and use in the UK are available in both VHF and UHF wavebands. Systems in the VHF range 173.800 MHz to 175.000 MHZ and the UHF range 863.100 MHz to 864.900 MHz are free to use, but you’ll need a license for anything that falls outside these.

Online Guide Radio Mics

Types

Getting the right wireless system depends on the application – are a solo singer, a corporate presenter, an aerobics teacher or a saxophonist? Each microphone and transmitter type should be chosen with the intended use in mind. Following are the most common mic/transmitter combinations, along with a brief explanation of their applications.

Handheld Mics

Ideal for singers on stage, presentations or audience participation shows, where a mic needs to be passed from one person to another.

Instrument Clip-on Mics

Specially designed for wind instruments where the mic is usually attached to the bell, and the transmitter worn by the player so that soloists are not tied to the mic stand - perfect for JB horn moves! Of course the instrumentalists most commonly wanting to go wireless are guitarists – this is a subject in itself, so please see our separate guide to this topic.

Lavalier Mics

Aimed at presenters and public speakers, these small microphones clip onto clothing whilst a wire runs underneath and connects to a small belt-pack transmitter which runs on batteries. They are unobtrusive, and allow the speaker to make full use of the stage. Very small versions of these mics are often used in theatres and hidden in hairpieces or camouflaged with make-up.

Headset Mics

Like Lavaliers, these connect to a belt-pack transmitter and are designed for those on stage making vigorous movements, or where high volumes require the mic to be very close to the mouth. Prime examples are singing dancers and guitarists, drummers, fitness instructors (look for sweat-proof headsets) and demonstrative presenters, where a lavalier might pick up clothing noise as they wildly gesticulate!

Online Guide Radio Mics

Multi-Mic Systems

Receivers

The choice of receiver should be based on both where it will be used and the complexity of the wireless system, as both will have a bearing on the level of interference and the number of channels required. Cheaper systems generally only have a fixed single channel rather than the ability to tune to a particular frequency. This is fine if you’ll only use a few mics, providing you ensure when you purchase them that each one has a different frequency. Manufacturers often colour code the boxes to make this easier. With multi-mic systems however, where more complex frequency management is necessary, a receiver that can tune to a range of different frequencies is required. You should also consider whether a diversity receiver is appropriate – see the Key Terms section for a full explanation.

Transmitters

Transmitters require power over and above anything that might be provided for the mic itself, and this will either be in the form of standard alkaline ‘Duracell’ type batteries, or a rechargeable battery pack supplied with the transmitter. Alkaline batteries generally last up to about six hours, as opposed to around three for rechargeables - either way, make sure you have full power before the show begins!

Online Guide Radio Mics

Key Terms

On this page you can find frequently asked Key Terms:

Pregunta:
VHF
Respuesta:
Very High Frequency - covers the radio frequency spectrum from 30M Hz to 300 MHz and is used mostly for TV broadcasting and FM radio.

Pregunta:
UHF
Respuesta:
Ultra High Frequency - covers the radio frequency spectrum from 300 Mhz to 3 GHz and is used mostly for TV and mobile phone services.

Pregunta:
Diversity
Respuesta:
All radio systems are susceptible to interference, and in extreme cases the signal can cut out altogether. To avoid the likelihood of this, ‘diversity’ receivers use two aerials spaced a distance apart. The signal received on each aerial is compared by the receiver, and the system automatically uses whichever is the stronger. As it’s unlikely that both aerials will ever experience drop out simultaneously, the resultant signal is very stable. (Diversity receivers do not require diversity transmitters – the aerials are merely picking up two different versions of the same signal due to their physical separation in space.) Systems with only one aerial are known as ‘non diversity’ - these should only be used when your budget is tight and the operating range of the system will be short.

Pregunta:
Interference
Respuesta:
This refers to problems of interaction with other electronic equipment. There are three common types of interference - electrical interference, radio frequency interference or ‘RFI’, and intermodulation (see below). Electrical interference can be caused by any electrical device, for instance computers, lighting and domestic products such as hi-fis and ‘white goods’. RFI is caused by radio, TV and other equipment that generates radio frequency energy in its normal operation. Well designed radio mic systems will avoid all types interference, but the cheapest may not!

Pregunta:
Intermodulation
Respuesta:
This is a type of distortion where two or more radio frequencies interact, resulting in new frequencies not present in the original signal. This can happen when a receiver picks up two dissimilar frequencies that interact with its own electronics to produce sum and difference frequencies, manifested in a whistling noise. It’s often also called ‘Third Order’ Intermodulation due to the third order harmonic that is created - this can occur when two or more wireless systems are used together as they interact to create additional frequencies. The more wireless systems you use simultaneously, the more intermodulation problems are likely to occur. Some transmitters have frequency coordination software that attempts to eliminate the harmonics, and many manufacturers provide tables of frequencies that can be used safely together without intermodulation.

Pregunta:
Squelch
Respuesta:
This is a form of circuitry not unlike a noise gate that is often built into wireless receivers. It mutes the audio output when no RF signal is present, or only a very low one - this cuts out any extraneous ‘white’ noise that would otherwise be heard when insufficient signal is received from the microphone, or when the mic is switched off. Most receivers have an adjustable squelch threshold.

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