When Shure Brothers introduced the Vagabond 88 wireless mic system in 1953, its primary purpose was to replace the 20-foot cable attached to the microphone. The Vagabond was not expected to transmit a signal hundreds of feet. In the 1970s, wireless mics grew in popularity, particularly for in-studio TV production (think “person presenting the weather”) and for Las Vegas stage shows. Even then, the transmission distance was relatively short.
As wireless mic technology improved, transmission distances increased. Eventually, the pro audio world began to ask the wireless mic to replace a 200-foot cable run, not just a 20-foot mic cable. So, antennas were moved farther away from the stage, often positioned by the mixing console for the sake of convenience. This antenna relocation method worked well for decades, primarily because far fewer RF [Radio Frequency] signals were in the air.
Now the trend has changed due to the ever-increasing level of RF background noise from digital TV stations, smartphones, Wi-Fi hot spots, wireless signage, etc. A high level of RF background noise can, and will, interfere with the reliable operation of wireless mics and wireless in-ear systems.
One method to combat increasing RF background noise is locating the antennas closer to the stage. If a UHF antenna is placed 20 feet away from a handheld transmitter, instead of 200 feet, the received signal can be up to 20dB stronger. 20dB = a factor of 100! The signal received by the antenna is 100 times stronger at the 20-foot distance, and this can often overcome an increase in RF background noise. Readers will ponder, “What about signal loss due to the length of the antenna cable?” Well, 200 feet of RG213U cable attenuates the signal by about 12dB. Even with cable loss the receiver is delivered 8 dB of additional RF signal: +20dB – 12dB = +8dB.
An alternate method is to locate the receiver [with antennas attached] near the stage, then run the audio signal back to the mixing board via a cable or snake. A low impedance, balanced audio connection can travel over 1,000 feet with negligible signal loss.
For wireless mic antennas, like some things in life, closer is better.
Related information: Wireless Systems Guide – Antenna Setup
Arcana – mysterious or specialized knowledge
The word “antenna” is based on a Latin nautical word meaning “yard arm.” A yard arm is the horizontal beam, fastened to the vertical mast, that holds the sail.
