Specifications

The last aspect of the use of wireless microphone
systems and the least predictable is radio interference.
Potential interference from other wireless systems
operating on the same or nearby frequencies has been
discussed, but what about other possible sources of
interference? High-band VHF systems are generally not
subject to interference from radio stations, amateur
radio, pagers or cellular telephones. Television stations
7-13 are a possibility but are very predictable. Always
avoid wireless microphone frequencies within the
bands of locally active TV channels. So-called travelling
frequencies (169 to 172 mHz) are available that are
just below the VHF television band. Keep in mind that
these travelling frequencies may be also used for
business two way radio or government use. If so, there
will likely be interference problems.
Unpredictable interference sources include the
following: 1) any type of digital device such as computers,
digital signal processors, DAT or CD players; 2) neon or
fluorescent light fixtures; 3) large motors and generators;
4) any electrical device that uses high voltage or high
current; or 5) any device that is marked with an FCC type
rating sticker.
Good practice with any wireless system is to check out
the system ahead of meeting time with all other systems
and devices activated. This will reveal potential problems
that were not apparent in a wireless system only test.
Many wireless receivers are equipped with an
adjustable squelch control. This sets the basic sensitivity
of the receiver to avoid picking up interfering signals, or
background radio noise, when the transmitter is turned off
or if a dropout occurs. It should be adjusted according to
the manufacturers’ instructions.
Ideally, transmitters should be turned on first, then
receivers. Once the system is on, use the mute or mic switch
to turn off the transmitter audio if necessary. Do not turn off
the transmitter until after the event is over and/or the receiver
is turned off. This will avoid an “open” receiver, which can
pick up other radio signals that may be present.
Finally, always use fresh batteries of the correct
type in the transmitter! Most manufacturers recommend
only alkaline or lithium type batteries for adequate
operation. Use rechargeable batteries with caution as
their actual voltage is usually less than stated, and they
may not operate satisfactorily in a wireless transmitter.
In addition, the actual operating time of a rechargeable
battery is normally much less than an alkaline type.
26
MEETING FACILITIES
Audio Systems Guide for
California Senate Meeting Room