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Selecting Frequencies
Wireless microphones are significantly different from other audio equipment in that wireless receivers and transmitters are radio devices that must operate on specific frequencies. If operating frequencies are poorly chosen, harmful interference is likely. Interference will seriously affect the operation of a wireless system and can even make it unusable. There are certain rules that must be observed if interference is to be avoided. The most important ones are:- Each transmitter requires a separate receiver on the same frequency.
- Two wireless systems in the same location cannot use the same frequency.
- Wireless frequencies cannot be too close to each other, otherwise harmful interference will result. In general, 1 MHz is the recommended minimum spacing between systems.
- Wireless systems cannot share frequencies with TV stations; they must not operate on frequencies that are the same as those used by local TV stations.
- Even when wireless frequencies are not the same, or too close together, or shared with a TV station, they can still occasionally interact with each other and cause self interference.
- There is a maximum number of wireless systems that can be operated in one location, and this number depends upon the specific model or type of wireless equipment in use and the local RF environment (operating TV stations, etc.).
- Just because a wireless system works perfectly in one area or in one particular situation does not mean that it will necessarily work equally well in another area or in another situation.
When you buy or rent a wireless system, someone has to select an operating frequency (for fixed-frequency systems) or an operating frequency range (for frequency-agile systems). This might be you, the dealer or rental company, or the wireless manufacturer. If the choice is made at random, there is a significant chance that there will be interference, especially with fixed-frequency systems. Thus, simply buying or renting the system that happens to be in stock creates an unnecessary risk. It is very important that you, or the dealer, or both, make an active effort to avoid frequency conflicts.
The easiest approach is to simply buy or rent from a dealer who is trained and equipped to perform frequency selection. There are various ways of accomplishing this, depending upon the particular situation. Always ask for this service; do not assume that it has been provided. To do this job correctly, the dealer will need to know two things, and you will usually need to provide this information. They are:
- The location or area where the wireless system will be used. Alternately, the channel numbers of the local TV stations can be provided. This allows the dealer to avoid TV frequencies when selecting frequencies.
- The frequency, model and type of any other wireless microphone systems that will be in use at the same location. This allows the dealer to avoid using the same frequencies, frequencies that are too close together, or frequencies which interact. It also allows the dealer to determine if the maximum possible number of wireless systems will be exceeded.
If the dealer is not equipped to provide this service, you or the wireless manufacturer must go through the process of selecting appropriate frequencies. Back to Contents
