Handbook for Sound Engineers

558 Chapter 16

wears a headset (a boom microphone with one or two
earpieces) and can simultaneously transmit on one
frequency and receive on another. The wireless
intercom transmitter is virtually identical to a wireless
microphone transmitter, but the receiver is miniaturized
so that it, too, can be conveniently carried around and
operated with minimum battery drain.
Wireless microphones are widely used in television
production. Handheld models (integral microphone
capsule and transmitter) are used by performers “on
camera,” where they not only free the performer to walk
around and gesture spontaneously, they also avoid the
need for stage personnel to feed wires around cameras,
props, etc. Lavalier models (small pocket-sized trans-
mitters that work with lavalier or miniature “hidden”
microphones) are used in game shows, soap operas,
dance routines, etc., where they eliminate the need for
boom microphones and further avoid visual clutter.
For location film production, as well as electronic
news gathering (ENG) and electronic field production
(EFP), wireless microphones make it possible to obtain
usable “first take” sound tracks in situations where previ-
ously, postproduction dialogue looping was necessary.
In theatrical productions, wireless microphones free
actors to speak and/or sing at normal levels through a
properly designed sound-reinforcement system.
In concerts, handheld wireless microphones permit
vocalists to move around without restriction, and
without shock hazard even in the rain. Some lavalier
models have high-impedance line inputs that accept
electric guitar cords to create wireless guitars.
In all of the above applications where wireless
microphones are used, in the studio or on location, a
wireless intercom also is an invaluable communication
aid between directors, stage managers, camera, lighting
and sound crews, and security personnel. For cueing of

talent and crews (or monitoring intercom conversa-

tions), economical receive-only units can be used. In

sports production, wireless intercoms are used by

coaches, spotters, players, production crews, and

reporters. A major advantage is zero setup time. In crit-

ical stunt coordination, a wireless intercom can make

the difference between a safe event or none at all. For

more information on intercoms, refer to Chapter 43.

16.10.1 Criteria for Selecting a Wireless Microphone

There are a number of criteria that must be considered

in obtaining a wireless microphone system suitable for

professional use.19,20 Ideally, such a system must work

perfectly and reliably in a variety of tough environments

with good intelligibility and must be usable near strong

RF fields, lighting dimmers, and sources of electromag-

netic interference. This relates directly to the type of

modulation (standard frequency modulation or

narrow-band frequency modulation), the operating

frequency, high frequency (HF), very high frequency

(VHF), ultrahigh frequency (UHF), the receiver selec-

tivity, and so forth. The system must be very reliable

and capable of operating at least five hours on one set of

disposable batteries (or on one recharge if Ni-Cads are

used).

16.10.1.1 Frequency Bands of Operation

Based on the FCC’s reallocation of frequencies and

the uncertainty of current and future allocations, some

wireless manufacturers are offering systems that avoid

the VHF and UHF bands completely. The ISM (indus-

trial, science, and medicine) bands provide a unique

alternative to the TV bands. By international agreement,

Figure 16-144. Wireless microphone transmitter section with built-in preamplifier, compressor, and transmitter, and the
receiver with a built-in discriminator expander.

Microphone

Preamp Compression Transientmodulator

Antenna

A. Transmitter audio section. B. Radio frequency section.

Antenna

Receive

discriminator Expander

Audio

amp

Output

C. Receiver audio section.