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Illuminating The Dark Art: A Practical Step-By-Step Guide To Success With Wireless/RF

When approached systematically, managing RF for wireless microphone and IEM systems can actually be quite enjoyable in a nerdy kind of way!

By Becky Pell April 26, 2019

A screenshot of Shure's Wireless Workbench RF coordination software

Antenna Selection & Placement

Choose the right antennas. Do your homework and know the polar coverage of your chosen antennas, so you can keep that in mind when you position them. Use directional paddles instead of “twigs” for wireless mics, and if they’re active, it’s generally best to set them on the lower gain. (Higher gain means they pick up over a greater area, but they pick everything up, not just the frequencies you want, and 3dB is ample for most stage applications.)

It’s been my experience that helical or “bubble” antennas with IEM systems offer superior performance to a paddle due to the higher gain and reduced dropouts characteristic of its construction.

Minimize connections. Every connector in the path of an antenna cable results in some RF signal loss. Avoid extending RF cables, and use adaptors and panels only when absolutely necessary. RF signals always prefer traveling through air rather than cable, so keep cable lengths to a functional minimum – never use a 30-foot cable if a 10-foot cable will reach. If you need more than 30 feet, reassess the positioning of your racks to see if you can get them closer

Maintain direct line-of-sight between transmitters and receivers. An antenna that’s tucked around a corner and can’t ‘see’ the stage won’t do its job well, and keeping artist IEM bodypack antennas on the outside of their clothing is good practice where possible. You may have to negotiate with the wardrobe department if it’s a costume-heavy show, but it’s very normal for them to make a little fabric pouch for the pack to sit in.

Use the right cables. It’s easy to mistake a BNC cable that’s intended for the back of a desk (i.e., MADI) for an RF cable, as they have the same connectors – but they have different characteristic impedance and must be kept separate. RF uses 50-ohm cable, digital data uses 75-ohm. It’s also worth using a specific low-loss cable such as RG-213 with N-type connectors for IEMs – they’re thicker than standard cables and BNC connectors, and lose a smaller amount of RF signal – especially useful in circumstances where you have no choice but to run longer cables.

Get high. Height is our friend when it comes to antenna placement, so take stands up to their fullest extension. Diversity receiver paddles for radio mics can be close to each other – a minimum of 1/2 wavelength is good practice – the wavelength for a 700 MHz signal is about 40 centimeters (15 inches), so a wide T-bar on a single stand is fine. Keep some distance between receiver paddles and your IEM transmitter antenna though – I usually put my IEM antenna up high near the downstage edge of my desk and the receiver paddles at the upstage side.

Tuning Up

When I arrive at a gig but my gear is still on the truck, I use this time to have a look at the frequency ranges of my equipment on my handheld scanner to see what’s in store. Then once I’ve got everything set up and switched on, I’m ready to tune my frequencies. Here’s the rest of my process:

– If we’ve booked frequencies through a licensing body or the promoter has given me a list, I’ll use those; if I have free rein, then I can choose frequencies through comprehensive RF coordination software such as Sennheiser Wireless Systems Manager or Shure Wireless Workbench – or make use of the banks of compatible frequencies within the system by using the scan function of the receivers and seeing which bank reads the most clear frequencies.

– I then set the receivers and transmitters accordingly, and then switch all of the transmitters off and look at the receivers. The pre set-up can has already provided me with a pretty good idea what to expect, but if everything is quiet (i.e., receiving no RF at all) then I know I’m off to a good start – there’s no local interference in the frequencies I’m already tuned to.

– I switch on all of the transmitters back on and spread them out (both handheld mics and bodypacks) along the top of an adjacent flight case. I make sure the mic “tails” (where the transmit antennas are located) are pointing away from each other – if they’re all in a pile it can create proximity intermodulation that will totally cloud the next step.


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About Becky

Becky Pell
Becky Pell

Becky Pell is a monitor engineer with more than 20 years of experience in live sound. She toured as a monitor and RF tech with Black Crowes, Travis and Kylie Minogue before moving behind the desk to mix monitors for artists such as Aha, Muse, Westlife, Anastacia and Take That. Read more from Becky at SoundGirls.org.
http://SoundGirls.org

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