Part 2: PSW Wireless Primer
 
Avoiding Wireless System “Issues”
Although the popularity of wireless microphones continues to grow, there’s no denying that they present more opportunities for problems than their wired counterparts.

In addition to the normal acoustic concerns that come with any mic are the complications of RF (radio frequency) transmission, interference, frequency selection, batteries and several other issues.

And technical improvements in wireless systems have not entirely kept pace with increasing frequency congestion, digital television and other recent complications.

Still, the hundreds of thousands of wireless systems employed in the U.S. is compelling evidence that the majority of users will live with the added challenges. Besides, many of the problems encountered by wireless users are largely avoidable, and happen primarily due to oversights, mistakes and misunderstandings.

Addressing the following common issues greatly improves the reliability of wireless systems and goes a long way toward ensuring trouble-free operation.

Issue: Frequency planning and coordination. Wireless systems share the RF spectrum with TV stations and several other types of authorized users. As a result, interference is very likely unless appropriate precautions are taken.

Solution: The first step is to determine the TV channels that broadcast over the air in your area.

When the local TV channels are known, they can be compared to the frequencies of the wireless systems. If there’s a conflict, the wireless frequencies must be changed. This is relatively simple for synthesized systems as well as ones that search for vacant frequencies, but the solution is more difficult for fixed-frequency wireless.

Despite the inconvenience, wireless systems should not be used on occupied TV channels. Not only is interference almost certain, the practice is illegal. 

Issue: Intermodulation. Wireless systems can also experience severe interference even when operating on “vacant” frequencies. This is created by intermodulation distortion - basically two strong signals on other frequencies combining in the wireless receiver to create an interfering signal.

In one variation of intermod shown here, the frequencies of two wireless systems can combine to “gang up” on a third system.

Called “intermod” for short, generally this type of interference is more common than direct on-frequency interference from other transmitters.

Intermod is typically caused by other wireless systems, or by other wireless in conjunction with local TV signals.

Even single systems can be affected, but the probability of problems grows roughly proportionally to the square of the number of systems in simultaneous use, plus the number of active analog TV channels present. 

By the time eight or more wireless systems and six or more TV channels are involved, it can become quite challenging to find usable frequencies.

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