Technical Problems with Wireless Microphones

Transmission loss and dropout are the two technical problems with wireless microphones.

Transmission loss:

There is a calculated transmission loss between transmitter and receiver through use of an instrumentation antenna.  Less transmitter power is required for signal strength as the frequency is lowered.  One problem with wireless microphones is the difficulty in designing antennas that are small but can still pick up the VHF low-band area.  Small antennas work much better for the VHF high-band area

Interference from other radio signals is a major problem at both VHF and UHF. The only clear channels available are the unused TV channels in a given location and the “B” channels. For touring groups the

TV channels become a problem, as a clear TV channel in one city may not be clear in another. Therefore, the “B” channels are recommended for this purpose.

Dropout

Dropout is the terms used when a wireless signal is no longer making contact with the receiver, and can be caused by two things: Interfering radio waves, and physical objects.  Another factor to consider is that not all of the transmitting power coming from the transmitter is getting to the receiver, as the transmitter transmits in all directions.

Solutions:

Use of a High Gain Receiving Antenna at the Mix Position

High gain antennas can improve the signal to noise ration, reducing fade and dropout, but signal cancellation will not be helped. These antennas are also bad for two reasons; high gain antennas will have to be constantly re-aimed at the transmitter as it moves around, and since the receiver is so strong it will pick up signal bouncing off of walls, people, props etc.

Place the receiver closer to the transmitter.

Place the receiving antenna and receiver off stage so it can be as close the transmitter as possible.  This will allow the receiving antenna to be as close the microphone as possible.  This method works well as it will provide the best chance for signal strength.  The signal can them run from the receiver to the mix position via a standard audio cable.

Diversity Reception:

Diversity reception works on the principle that two heads are better than one.  Many wireless systems have two receivers for each transmitter.  The theory behind this is that one signal will be stronger than the other, so the receivers will switch back and forth so it will always have the strongest signal possible.  Technically, you can send signal to as many receivers as you want, but getting them to work together and switch automatically is very difficult.  This will not help you with dead spots though.

The theories and calculations are far beyond the scope of necessary understanding outside of a huge production, so I will spare you the headache, but if you would like the technical information, just let me know in the comments section.

-By John Redick

Click here to learn the basics of wireless microphones

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