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Change Is In The Air

What's happening with wireless mic, IEM and comm systems, as well as best practices to help prevent problems

By PSW Staff November 24, 2015

The reshaping of entertainment production wireless operations in the U.S. is currently underway, and it will impact all wireless microphone, in-ear monitoring and intercom system users – including those working in church sound – in the near future.

The shrinking UHF band, where the vast majority of wireless systems currently operate, will get even smaller with the 2016 commencement of the 600 MHz incentive auction to allow the mass introduction of white space devices. Almost all of the remaining UHF spectrum not occupied by digital television, and used by wireless system operators, will be shared with these devices.

A recent report on ProSoundWeb (here) by noted wireless technician and frequency coordinator James Stoffo provides further details. Anyone working with wireless systems is highly encouraged to take advantage of this crucial information.

In light of the situation, it’s not surprising that the VHF band is getting renewed interest. Incorporating new manufacturing techniques and sophisticated DSP technology into VHF products eliminates many of the RF (radio frequency) and audio quality issues from a generation ago. In fact, Stoffo notes that at least a few leading manufacturers are already developing VHF systems.

In the meantime, it’s more important than ever to follow best practices. Addressing the following common issues greatly improves the reliability of wireless systems and goes a long way toward ensuring trouble-free operation.

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

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 frequencies must be changed. This is relatively simple for synthesized systems as well as ones that search for vacant frequencies, but is more difficult with fixed-frequency wireless.

Avoid intermodulation. Wireless systems can also experience severe interference even when operating on “vacant” frequencies. This is created by intermodulation distortion, called “intermod” for short, which is basically two strong signals on other frequencies combining in the wireless receiver to create an interfering signal.

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. 

The solution is that one or more wireless frequencies will have to change. Again, synthesized systems and auto-search frequency finding can be helpful. However, any frequency can potentially interact with any other, so changing a frequency to solve one problem can create another (or several others).

When changing frequencies or searching, it’s critical that all RF systems of any type at the location be turned on and operating. As one clear frequency is found, that system must be left on, and the next system tested until all are operational.

Otherwise, the situation can quickly become a snarl of changes and more changes. Some manufacturers offer assistance in this regard, and there are a number of software packages that aid in calculating frequencies.

Shielding or covering antennas. For efficient operation, all antennas must be kept clear of metallic objects that can weaken and distort signals, in addition to reducing range. With bodypack transmitters, the antenna must be kept away from the mic cable, the bodypack case and ideally, the wearer’s body.

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