used. Oftentimes, 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 system is used. However, this is an acoustic problem and is not directly related
to the use of wireless transmission. Solutions to this problem include substituting a
directional lavalier microphone (a few such units are available), reducing the monitor
level, or relocating the monitor speakers.
Antennas/Cables
As noted in the section on antennas above, selection, placement, and mounting are
vitally important. Shielding of the antenna with metallic objects not only will reduce the
signal level available, but may result in creating locations within the coverage area
where the receiving antenna is almost entirely ineffective (pattern “nulls”). If a
coverage problem exists, it is always advisable to try moving the receiving antenna,
particularly if there are nearby metallic materials.
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, car ignitions, 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,
because normally functioning fixtures almost never cause trouble. This situation is true
for most other interference sources as well. That is, unless the equipment is electrically
defective, the interference will not adversely affect Vega wireless equipment. When
such a situation exists, the source has become a wideband transmitter and nothing can
be done to the wireless equipment to correct the problem that will not seriously degrade
performance. Fortunately, this type of problem is very rare.
A more serious problem is selecting wireless-microphone operating frequencies which
are inherently subject to interference due to intermodulation. Fortunately, a proper
initial selection of or changing frequencies will almost always correct any such
problem. Vega offers a free computerized frequency-selection service to purchasers of
its equipment. If the frequency of other wireless equipment to be used in a given area is
known, interference-free frequencies can be chosen. However, if equipment is added
later without frequency coordination, an interference problem will likely exist. Should
this occur, contact the Vega factory or your sales representative for assistance. Contrary
to popular belief, a dozen or more wireless systems may be used in an area, with
careful frequency coordination.
Microphone Problems
A few electret microphones are sensitive to RF energy and require special precautions
to operate properly with wireless transmitters. This includes several types of Sony
microphones, some Beyer and AKG units, most types of Audio-Technica microphones,
and several others. If the sound quality of a microphone changes drastically when its
position with respect to the transmitter changes, RF susceptibility is likely the cause.
Contact the Vega factory or your sales representative if assistance is required.
The wires in lavalier electret microphone cables are usually very small. After a period
of heavy use, the conductors may fray, resulting in intermittent failure or severe noise.
Of course, an outright break may also occur, but this is usually easy to identify and
correct. It is advisable to have a spare microphone available which is known to be in
good working condition (it does not need to be a high-quality unit). With a spare
microphone, it becomes easy to localize problems due to bad microphone cables by
merely substituting the spare for the suspected unit.
Wireless-Microphone Receiver 9
