How Close Should My Wireless Antenna Be to the Transmitter?

When professional wireless mic systems were first introduced in 1953, they were intended to replace a typical 20 foot microphone cable. At this point, they were never designed to transmit over hundreds of feet as they sometimes are today. Throughout the 20th century, wireless mics grew exponentially in popularity – particularly for TV production and live stage shows. Transmission distance, however, remained short until relatively recently.

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As wireless mic technology improved toward the latter half of the century, the transmission distances gradually increased. Eventually, as production values developed, wireless microphones were replacing anything up to and around 200 foot of cable run. Antennas were moved further away from the stage and could often end up by the mixing console for convenience. This kind of antenna setup worked ok for many decades, primarily because there just weren’t that many RF devices in operation.

Today, however, is an entirely different story, with the level of RF background noise increasing dramatically from new digital TV stations, smartphones, Wi-Fi hotspots, and even wireless signage. High levels of RF noise can play havoc with the operation of wireless mics and in-ear systems; therefore, good antenna placement is critical.

One very simple way to combat the increasing noise is simply to move your antennas closer to the transmitter. If a UHF antenna is placed just 20 feet away from the transmitter instead of 200 feet away, the signal can be up to 20 dB stronger. Put another way, the signal is up to 100 times stronger, and this can help significantly in the battle against RF background noise.

But What about Signal Loss over a Long Cable Run?

Signal loss can be a factor, and we wouldn’t advocate running 200ft of coaxial cable if you can help it. But, when the antenna distance is kept short, even very long coaxial runs can still operate when factoring in the stronger signal. Here is an exaggerated example to prove the point:

200 feet of RG213U cable will attenuate the signal by about 12 dB. Even with this level of cable loss the receiver is delivered a greater level of RF signal when the antenna is only 20ft away. For example:

+20dB stronger signal – 12 dB from cable loss = +8 dB.

You get the point – closer is better!

Furthermore, and while we’re on the topic of signal loss over coaxial cable, if this does prove to be a problem, you may want to consider an antenna amplifier to overcome the signal loss over distance. Alternatively, another method is to place the receiver with the antennas near the stage. From here you can run the balanced low impedance audio signal back to the mixing board via a cable snake. The signal will remain of high quality because balanced low impedance audio signals can be run over 1,000 feet with negligible signal loss.

In conclusion, when all is said and done – get those antennas closer to the source for more peace of mind.

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RF spectrum can seem complex. And, with the recent changes coming thick and fast, it can all seem like a lot to take in. If so, you’re not alone. Keep up to date with the latest changes and get your FREE guide to wireless frequencies in the UK by visiting LosingYourVoice.co.uk

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Marc Henshall

Marc forms part of our Pro Audio team at Shure UK and specialises in Digital Marketing. He also holds a BSc First Class Hons Degree in Music Technology. When not at work he enjoys playing the guitar, producing music, and dabbling in DIY (preferably with a good craft beer or two).

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