nofars.net

WIRELESS MICROPHONES

By Ross Goodall, WD4NJV

Wireless mics are used to transmit sound to an amplifier or recorder without cables.  They are used by broadcasters, music concerts, public events, churches and schools.  

Some systems are used for high end professional applications.  Some are single frequency and others will cover many frequencies on a band. Many use spectrum in the current television channels 2-51 except 37.  

The FCC allows both licensed and unlicensed wireless microphones.  The FCC’s rules allow licensed wireless mics on unused television channels on a secondary basis under Part 74.

 A large entity can be licensed if they are routinely using 50 or more devices for events or productions.  The following are frequencies commonly used:

944-952 MHz broadcasters and 169-172 MHz broadcasters (narrow bandwidth) Part 74 license required.

902-928 MHz, 1920-1930 MHz, and 2.4GHz low power unlicensed Part 15

Unused Television channels low power unlicensed Part 15:

A-1 Band 470-516 MHz, A Band 516-558 MHz, and G Band 556-608 MHz.
600 and 700 MHz BAND (608-806 MHz) as of 2010 repurposed for wireless broadband and public safety services. (1) ** 

Wireless microphone systems allow performers and presenters to move about freely which would be almost impossible and a distraction with wired systems.  

To set up most systems first turn on the receiver and second turn on the transmitter.  Most systems have an automatic frequency selection function.  

If the volume is to low increase the volume at the transmitter and if it is too loud reduce the volume at the transmitter.  There are different system types:

1. Handheld mike with transmitter

2. headset mikes with body pack transmitter

3. Lavalier mic with body pack transmitter

4. Instrument systems working with musical instruments. (2)

In my opinion it is best to purchase a quality system. Users of the system must understand that the quality systems need to be given care in handling.

No dropping the mike etc. Wires from the transmitter to the mic are subject to wear and tear where the wire goes into the jack.  It would be advisable to have an extra mic available should the cord develop a short.

The sound person’s job is sometimes not regarded as important but it is very important to make the performer sound great.

Any sound problems such as a dead battery make the sound tech appear nonprofessional. The board operator must open and close the audio at the right time and anticipate what is next on the program.  

I believe that it is very important to check the wireless mic transmitter battery before every use with a professional quality battery tester and do sound checks before the event starts.  

I have noticed that one professional organization I have worked with using wireless systems for television broadcast installs a new Duracell battery before every use and the old one is discarded and keeps a box of unused batteries on hand as spares.  

Frequency coordination is essential in large events such as witnessed in the Super Bowl held in Jacksonville. Without coordination when all units are active interference can be a monumental problem.

References:

(1)    FCC.Gov, Wireless Microphones

(2)     Sweetwater.com, Wireless Microphone Buying Guide.

** Some frequency assignments for wireless microphones have changed since this article was written.

JaxRadio.net