At some point in time, for whatever reason, you will need to expand your wireless installation from a microphone or two to, say, eight or 10. Whether this growth comes as a planned, permanent expansion, or whether your church is producing a large-scale musical or an Easter drama event, there are steps you can take that will make the process as painless as possible.

Of course, put simply, the idea of a wireless system is to provide the performance of a wired microphone or instrument with the convenience and flexibility of a radio link between a transmitter — either a body pack into which a microphone or musical instrument can be plugged, or a hand-held microphone unit — and a receiver that will generally be connected to your mixing console and/or PA system. The receiver and the transmitter both must be operating on the same frequency. If any two transmitters are operating on the same frequency, severe interference will result and the wireless system will be unusable.

You can “use” a handheld and a body-pack transmitter with one receiver, but only one at a time.

Choosing Your Frequencies
With one or two units, as you may discovered, you can plug the system in, cross your fingers and it will probably work. The only real potential problems have to do with interference caused by frequencies already in use in your area, typically for TV stations.

There may also be interference caused by other wireless systems operating in adjacent areas (the youth service in the basement, the church across the street etc). These problems, however, are relatively simple to overcome, simply by choosing vacant frequencies.

It will help immensely if the wireless systems you choose are “frequency agile”, as is the case with most modern units. This means that you can select from a variety of frequencies rather than being limited to a single preset frequency. Also, make certain that the transmitters are ten feet or more away from the receivers to avoid overloading the system.

The Power of Three
Problems really start to emerge when you cross the threshold from two wireless units to three, and they get worse as you add more devices. The fundamental problem is that of Third Order Intermodulation. When you get more than two wireless units together, they interact to create additional frequencies.

As the number of systems increases, intermodulation problems increase exponentially. This is why it is vital to carry out careful frequency planning before you start. This problem applies to all manufacturers, and it applies whether all your units are made by the same company or by more than one.

Many wireless system manufacturers provide tables of frequencies that can be used together without intermodulation problems, and it is worth consulting your instruction manual, equipment dealer, or visiting your system manufacturer’s web site to see what tools are available to help you.

The Audio-Technica web site, for example, includes a frequency selection system entitled “Checking Frequency Compatibility” that will enable you to find usable frequencies whether you are using AT systems or those from other manufacturers. (See www.audio-technica.com/using/wireless for this and other useful tips on wireless operation.)