system is encountered, since a low battery may affect system operation in subtle
ways.
Receiver Noise
Vega wireless microphone receivers are designed to be extremely sensitive.
Although high-performance squelch circuits are provided, it is not unusual for the
receiver squelch to open and let through audio noise when the transmitter is off.
This is usually due to second-harmonic output of FM radio stations, spurious
outputs from two-way radio transmitters, adjacent-channel leakage from TV
transmitters, and, in some cases, RF noise from digital equipment such as audio
and video effects generators, computers, and other industrial equipment that may
be located near the antennas. When the wireless transmitter is “on”, this noise is
suppressed and rarely causes any difficulties. However, if the audio channel is left
“open” with the transmitter “off”, loud blasts of noise may occur. For this reason,
it is advisable to “fade” the receiver audio when the transmitter is not in use.
Changing the placement of the antennas and, in some extreme cases, changing the
operating frequency may be necessary to minimize these problems.
Antennas/Cables
As noted in the section on antennas above, antenna placement and mounting are
vitally important. Shielding the antenna with metallic objects reduces the signal
level available, and may create locations within the coverage area where the
receiving antenna is almost entirely ineffective (pattern “nulls”). If there is a
coverage problem, try moving the receiving antenna, particularly if there are
nearby metallic materials.
Acoustic Feedback
Bodypack transmitters usually use lavalier electret microphones. Almost all such
microphones are omnidirectional (equal sensitivity in all directions) and usually
pick up more ambient noise than the handheld microphones to which performers
are accustomed. The characteristic “sound” of lavalier microphones is also quite
different from the usual dynamic handheld microphone, partially because they are
electrets and usually sound “brighter” than dynamics.
In many sound systems, on-stage monitors are used. Often, the directional
characteristics of handheld microphones provide the only protection from acoustic
feedback. Omnidirectional lavalier microphones do not provide the same degree
of protection, and acoustic feedback may occur when the wireless is used.
However, this is an acoustic problem and is not directly related to the use of
wireless transmission. There are several solutions to this problem: substituting a
directional lavalier microphone (a few models are available), reducing the monitor
level, relocating the monitor speakers, or careful adjustment of equalizers.
Interference
Vega wireless-microphone systems have been specifically designed to reject
interference. However, interfering signals may fall directly on the receiver
frequency, making it impossible to avoid problems completely. As mentioned
above, this can be a particular problem if the receiver audio is left open when the
transmitter is turned off. Problems with RF noise sources (fluorescent lights,
digital effects generators, industrial equipment, etc.) are quite rare. However,
defective fluorescent lighting fixtures can generate astonishing amounts of RF
energy. Usually, repairing the fixture will cure the problem, since normally
functioning fixtures almost never cause trouble. Some digital audio and video
signal-processing equipment and effects generators also can generate substantial
amounts of broadband noise. When this situation exists, nothing can be done to
the wireless equipment to correct the problem that will not seriously degrade
UHF Wireless-Microphone Bodypack Transmitter
9