Basic Training for Sound System Operators
Articles from Pro Comm's Quarterly Newsletter
Wireless Microphone Systems from Sound Advice
Are you concerned about finding a wireless microphone system what works on a consistent basis for a reasonable cost?  Do you avoid using the wireless microphone because of some "war stories" about stray interference during a service or presentation?  Maybe you've heard of interference caused by CB'ers, fluorescent light ballasts, car engines, cordless phones or garage door openers.  Maybe you've asked yourself "how far away can I be from the receiver without losing the signal?  Can I find an economical wireless system that is also reliable?  If so, what features should I look for in that system?"

There are three frequency bands which wireless microphone bands operate on.  They are Lo band VHF (25-50 mHz and 72-76 mHz), Hi band VHF (150-216 mHx), and UHF (450-488 mHz and 902-952 mHz).  Lo bands have a definite cost advantage, but they are also much more susceptible to interference from cordless phones, toys, garage door openers, and occasional interference from sources a long way away due to atmospheric conditions.  UHF is of high quality and comes with a higher price, although prices are becoming increasingly more affordable.  For this discussion we will concentrate on the Hi band VHF systems.

Should the system have a compander?  Yes--without compressor/expander circuitry most wireless systems are limited to a signal to noise ratio and dynamic range of 50 dB.  Companders extend these specifications to exceed 80 dB or better.  A system without a compander should not be considered for most professional applications.


Choose a reliable system


Have it demonstrated so you know what you're buying.

Choose the proper frequency

Install antennas in the right locations


Understand the differences between Nicad and alkaline batteries


Regularly inspect equipment to uncover any slowly developing user or wear problems.

Do you need diversity operation and more than one receiving antenna? It depends. 

Answer #1: If the operating distances between the transmitter and the receiver are short, single antenna operation will likely be fine.  The structure of the building is very important.  If there is very little metal to reflect the radio waves, then a single antenna will probably work very well at normal distances in churches or schools.
Answer #2:   If the wireless system will be in use with other professional audio gear and you require absolute interference free performance, then seriously consider diversity.

A "signal dropout" can occur at any operating distance and is caused by the direct signal from the transmitter (called multi-path) arriving at the single receiving antenna out of phase. For example, you are listening to the FM radio in your car, pull up to a stoplight and all of a sudden, the signal "swooshes" and drops to a very low noisy level.  You're at a dropout location--the antenna on your car has picked up both direct and reflected signals at once.  If you pull up a few feet your car will come out of the dropout area and receive normally.

The solution to this problem is to use two antennas (diversity) at different locations.  Within the receiver, some manufacturers use two separate receivers, and switch to the receiver with the best signal.

Another system is the mixed/phase related diversity system.  This is a reliable system where two antennas are used on one receiver.  The internal diversity circuit monitors the overall antenna performance.  If signals arriving from the transmitter happen to be heading toward an "out of phase" condition, which would normally result in a fade or noise-up, that phase difference between the two antennas is modified until the signals add in phase. The system is noiseless and extremely effective at a reasonable cost.

How to Install a Wireless System

Receiver/Antenna Location
When installing a wireless system, it is always a good idea to keep the distance between the  transmitter and receiver/antennas as short as possible.  For instance, if you have the choice of concealing the receiver and antennas near the platform, or 250' away at some other location, choose the nearer.  Even though the system may have performed flawlessly when you originally tested it by walking all the way down to McDonald's on the corner, the field strength of your wireless has decreased significantly.  Therefore, if interfering outside signals are present near you system's frequency, the receiver may decide to capture the other signal.  The outside interference is probably at a very low level, but is now strong enough in relationship to your own transmitter's reduced signal strength to capture the receiver.

Wireless Equalization
When installing any new microphone, whether wired or wireless, attention should be given to the effect it may have on the overall frequency response of the sound system.  Installing an omnidirectional lavalier wireless system in a sound system originally equalized for handheld dynamic microphones may not work properly or sound very good.  Remember, all that is usually needed is re-equalization of the sound system, eliminating feedback and providing the desired tonal quality.

Common Wireless System Problems

Shattered crystals or component failure are seldom the culprits in wireless microphone failures.  More often than not the problem lies with

  • Poor antenna location
  • Non-alkaline throwaway batteries
  • Using the wrong type of rechargeable battery
  • Defective microphone or antenna, connectors and cables
  • Open mic elements
  • Broken transmitting antenna
  • Frequency interface
  • Improper audio gain settings and equalization

Wireless microphones are reliable if properly chosen and properly installed.  With good follow-up maintenance, most systems will provide years of cordless, trouble-free performance.