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Do you need diversity
operation and more than one receiving antenna? It depends.
Answer #1: If the
operating distances between the transmitter and the receiver are short,
single antenna operation will likely be fine. The structure of the
building is very important. If there is very little metal to reflect
the radio waves, then a single antenna will probably work very well at
normal distances in churches or schools.
Answer #2: If the wireless system will be in use with
other professional audio gear and you require absolute interference free
performance, then seriously consider diversity.
A "signal dropout" can occur
at any operating distance and is caused by the direct signal from the
transmitter (called multi-path) arriving at the single receiving antenna out
of phase. For example, you are listening to the FM radio in your car, pull
up to a stoplight and all of a sudden, the signal "swooshes" and drops to a
very low noisy level. You're at a dropout location--the antenna on
your car has picked up both direct and reflected signals at once. If
you pull up a few feet your car will come out of the dropout area and
receive normally.
The solution to this problem
is to use two antennas (diversity) at different locations. Within the
receiver, some manufacturers use two separate receivers, and switch to the
receiver with the best signal.
Another system is the
mixed/phase related diversity system. This is a reliable system where
two antennas are used on one receiver. The internal diversity circuit
monitors the overall antenna performance. If signals arriving from the
transmitter happen to be heading toward an "out of phase" condition, which
would normally result in a fade or noise-up, that phase difference between
the two antennas is modified until the signals add in phase. The system is
noiseless and extremely effective at a reasonable cost.
How to Install a Wireless
System
Receiver/Antenna Location
When installing a wireless system, it is always a good idea to keep the
distance between the transmitter and receiver/antennas as short as
possible. For instance, if you have the choice of concealing the
receiver and antennas near the platform, or 250' away at some other
location, choose the nearer. Even though the system may have performed
flawlessly when you originally tested it by walking all the way down to
McDonald's on the corner, the field strength of your wireless has decreased
significantly. Therefore, if interfering outside signals are present
near you system's frequency, the receiver may decide to capture the other
signal. The outside interference is probably at a very low level, but
is now strong enough in relationship to your own transmitter's reduced
signal strength to capture the receiver.
Wireless Equalization
When installing any new
microphone, whether wired or wireless, attention should be given to the
effect it may have on the overall frequency response of the sound system.
Installing an omnidirectional lavalier wireless system in a sound system
originally equalized for handheld dynamic microphones may not work properly
or sound very good. Remember, all that is usually needed is
re-equalization of the sound system, eliminating feedback and providing the
desired tonal quality.
Common Wireless System
Problems
Shattered crystals or
component failure are seldom the culprits in wireless microphone failures.
More often than not the problem lies with
- Poor antenna location
- Non-alkaline throwaway
batteries
- Using the wrong type of
rechargeable battery
- Defective microphone or
antenna, connectors and cables
- Open mic elements
- Broken transmitting
antenna
- Frequency interface
- Improper audio gain
settings and equalization
Wireless microphones are reliable if properly chosen and properly installed.
With good follow-up maintenance, most systems will provide years of
cordless, trouble-free performance.
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