On stage, everything wireless draws on the same scarce, contested resource: the radio spectrum. Handheld mics, bodypack transmitters, in-ear monitors, intercom systems: the moment you line up several links, the question is no longer whether they will interfere, but how to make them coexist cleanly. RF frequency coordination is exactly that groundwork, the difference between a reliable show and a stage that crackles. Here is how to do it with method.
Why RF coordination is no longer optional
There was a time when you could put two wireless mics side by side without a second thought. That time is gone. The shrinking of available bands after spectrum was sold off to mobile networks, the density of wireless gear on a modern stage, and the coexistence in one room of Wi-Fi, walkie-talkies and video links have turned a casual act into a discipline of its own. A moderately ambitious festival easily runs twenty to forty simultaneous carriers across mics, IEMs and intercom. At that scale, improvisation is unforgiving.
The good news is that coordination rests on a handful of stable principles. Once you grasp them, you reason correctly whatever the channel count.
The basics: carrier, spacing and bandwidth
Every wireless link occupies a carrier, a centre frequency in megahertz. Around that carrier the signal is not infinitely narrow: it takes up a certain width. Two links too close in frequency will therefore encroach on each other, even if their carriers are not exactly identical. First rule, then: keep a minimum spacing between neighbouring carriers, typically a few hundred kilohertz, a figure the manufacturer specifies for each range.
You also have to stay inside a coherent band, a frequency range where your transmitters and receivers are designed to work and where use is permitted. This is a regulatory matter as much as a technical one: depending on the country and the event, some portions of the spectrum are licence-free, others licensed, others off-limits. Working in the wrong band exposes you to interference and to trouble.
Enemy number one: intermodulation
If coordination were only about spacing between carriers, it would be trivial. The real adversary is intermodulation. When two or more frequencies mix in a receiver’s front end or in a transmitter, they generate new spurious frequencies, sums and differences of their multiples. The most feared case is the so-called third-order product: with two carriers A and B, spurious signals appear around 2A minus B and 2B minus A, often very close to the carriers you actually use.
In other words, two perfectly spaced frequencies can manufacture a third one that lands right on a channel you wanted. That is why you never pick frequencies by hand on a large system: coordination software computes compatible sets in which no troublesome intermodulation product falls on an active carrier. That calculation is the heart of the craft.
Building a frequency plan, step by step
A frequency plan is built in a logical order, and that order matters as much as the result:
- Inventory the needs. List every link to coordinate: mics, IEMs, intercom, spares included. One forgotten carrier means a plan to redo.
- Scan the environment. Before placing anything, measure what already occupies the spectrum on site: local TV, other vendors, house links. You coordinate around what exists, not against it.
- Define the working bands. Choose the permitted ranges free of strong interferers, then spread your device families across them.
- Compute the compatible sets. Let the coordination software generate frequencies free of troublesome intermodulation, accounting for spacing and third-order products.
- Deploy and lock. Transfer the plan into transmitters and receivers, then lock the settings so a last-minute tweak cannot break the set.
One simple principle guides all of this: separate the critical uses. The lead singer’s mic and the drummer’s IEM must never hang on a fragile channel. Keep a few coordinated spare frequencies ready to go, too, because an interferer can appear on show day without warning.
Scan, coordinate, document
The scan is not an opening formality: it is a reading of the venue at a given moment. A room’s spectrum changes from day to day, sometimes hour to hour, as other users come and go. Many modern receivers can scan their surroundings and suggest free frequencies; on a large system you prefer a centralised scan exported to the coordination software, which sees the whole picture rather than channel by channel.
Then comes the part everyone neglects and pros never skip: documentation. Write down the plan, the assigned frequencies, the spares, the antenna zones. The day a link drops mid-show, that sheet buys you the thirty seconds between an invisible incident and dead air.
Antennas and coverage
A perfect frequency plan is useless if the signal does not reach the receiver cleanly. Coordination therefore goes hand in hand with antenna management: remote antennas as close to the stage as possible, combiners to pool IEM links, antenna distribution for the mics, and constant attention to line of sight. A bodypack hidden behind a metal set piece or a body in the way, and the best plan in the world will not save you from a dropout. The field rule: bring the antennas closer, clear the line of sight, and only raise transmit power when it is truly necessary.
Field traps
After enough stages, you end up with a blacklist. The classic trap is the link added at the last minute on a frequency picked free by eye, which reintroduces an intermodulation product into an otherwise clean plan. Another regular: turning up transmit power to compensate for a bad antenna, which overloads the front end of nearby receivers and creates interference where there was none. Finally, the temptation to reuse yesterday’s plan as-is in another room: the spectrum has changed, the plan must be recomputed.
My take, forged in live and event work: RF coordination is not the glamorous part of the job, but it is one of the most rewarding in peace of mind. An hour spent scanning and coordinating properly spares you the worst quarter-hours of a show, the ones where a link fails under the lights. It is an investment, not a chore.
In short
Coordinating your RF is about understanding that every link shares a common resource that has to be organised: keep the spacing, compute the intermodulation, scan the venue, document the plan and look after the antennas. The approach is the same for two mics or forty carriers, only the scale changes. That rigour extends the one you already apply to system work and to your monitors: it is the same engineering mindset applied to wireless, and it is inseparable from the reliability of your front-of-house tools and your stage sound, starting with the right live vocal mic.
