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.
- For multiple wireless system operation, wireless frequencies need to be separated so they do not cause adjacent channel interference with one another. That is typically any frequency that is greater than 250 KHz between channels but depends on the actual wireless model being used and itís capability. For multiple wireless system operation, each wireless system must be on an unoccupied frequency and the frequency must be clear of a third order intermodulation harmonics. A third order harmonic is created when two wireless transmitters are operated in close proximity to one another and they create a third RF signal that falls on a third wireless system frequency causing interference. Use the internal receiver scan function to find compatible frequencies if the scan feature is incorporated in your model of wireless.
- 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.
- 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.
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