You’re working with a rock band. Stage right and stage left both have guitar rigs, each with its own tech. Off stage left is monitor beach.
The stage right guitar tech scans around and sets his guitar wireless system at 550.000 MHz. The stage left guitar tech does the same and finds a clear frequency at 555.000 MHz. The monitor tech scans, and then puts the singer’s IEM pack at 560.000 MHz and his vocal mic at 545.000 MHz.
Everything sounds clean, checks out fine at sound check, and works great for most of the show until the two guitar players, who haven’t been speaking to each other for most of the tour, suddenly decide to have a Spinal Tap moment and do that leaning on each other’s backs shtick… which puts their guitar transmitters (belt packs) in close proximity.
Suddenly, the singer is tearing out his earbuds, shooting nasty looks at the monitor tech and trying to keep his pitch via the wedge mix (remember those?). After the show, there’s a whole bunch of speculation and shoulder shrugging about where this terrible interference came from, with everyone having their belief that wireless is inherently prone to this sort of thing firmly reinforced. But what can you do?
Each of the three techs choosing frequencies exercised due diligence and scanned for a clear frequencies, right? The real problem is that the frequencies were not properly coordinated, which allowed the guitar packs to create an intermod product that landed right on the singer’s IEM frequency (and his mic’s…).
This raises the question: How is frequency coordination different from scanning? Frequency coordination is predictive while scanning is reactive. Scanning can only show you what potential sources of interference are in a given area when you’re looking and when they’re happening. Coordination, on the other hand, can predict sources of interference and offer a selection of frequencies to avoid them.
You’re the stage manager at a sports arena, where a soul diva is about to sing the anthem. On your left hip, you’re wearing an RF intercom pack programmed to transmit on 620.000 MHz. Located to your left and looking lovely and focused, the diva holds a wireless mic tuned to 610.000 MHz in her right hand, at her side. And she’s wearing an IEM pack on her back tuned to 630.000 MHz.
You reach down, key your belt pack and tell the folks in the control room “I have the package, she’s ready to go.” As you do this, her hand shoots to her ear and a look of alarm passes over her face. You key your intercom again: “Hold a minute, there’s a problem.” The diva looks at you—there was that noise in her ears again!
I’m sure you get the picture by now. Your intercom Tx and her wireless mic are producing an intermod product that is landing on her IEM frequency—but only when you key your intercom to talk, and possibly, only when she has the mic by her side. You can’t scan for that, but you could have predicted it with a frequency coordination program.