1
Frequency Coordination: Why You Can't Just Pick Any Channel
You cannot just pick any open frequency for a wireless channel. When several transmitters run together, each pair generates intermodulation products, new spurious frequencies, and one of those can land on another channel and ruin it. A frequency that is clear on its own may still break the set.
So coordination means choosing a whole set of frequencies where no channel's intermod products hit any other. Software calculates it; always start from a fresh RF scan of the venue.
In practice: Eight wireless channels that worked yesterday but drop out today: the RF environment changed, re-scan, re-coordinate, retune all transmitters.
Coordinate frequencies as a set, intermod products from one channel can wreck another.
2
Intermodulation: Mixing Products and How to Avoid Them
When two RF signals are present together they mix and create intermodulation products, new frequencies at predictable spots (2A-B, 2B-A for third-order). Third-order products are the strongest and fall close to the originals, so they readily land on another channel and interfere.
This is the math behind frequency coordination: pick frequencies where no intermod product hits an operating channel. Corroded connectors can create intermod too (passive intermod).
In practice: Mics at 510, 530, 550 MHz: 2x530-510 = 550: the intermod of the first two lands exactly on the third. Coordination software finds a set that avoids this.
Combined RF signals create intermod products, coordination keeps them off every channel.
3
Antenna Diversity: Switching and True Diversity
Diversity uses two antennas to fight dropouts from multipath (reflected signals cancelling). Switching diversity has two antennas but one receiver circuit, it picks the antenna with the stronger signal. True diversity has two antennas AND two full receiver circuits, continuously comparing the actual demodulated audio.
True diversity is more reliable because it judges audio quality, not just signal strength, which matters most in metal-heavy, reflective venues. Space the two antennas at least a quarter-wavelength apart.
In practice: Wireless for a touring band playing reflective metal-staged theaters: true diversity handles the multipath far better than switching diversity.
True diversity = two antennas and two receivers comparing audio, best against multipath.
4
Antenna Placement: Fresnel Zone and Line of Sight
RF signals are not laser beams, they travel through a 3D elliptical volume around the line of sight called the Fresnel zone. Even with clear line of sight, an obstruction intruding into that zone, a speaker, truss, or a crowd of bodies, causes diffraction and signal loss.
So antennas need real line of sight and a clear Fresnel zone: elevate them above the audience, since human bodies (mostly water) heavily absorb UHF.
In practice: Wireless that worked at empty soundcheck but drops out with 800 people standing: the crowd is blocking the Fresnel zone, raise the antennas above their heads.
RF needs a clear Fresnel zone, not just line of sight, elevate antennas above the crowd.
5
Wireless Setup Workflow: Scan, Coordinate, Check, Label, Backup
Professional wireless setup is a fixed six-step sequence: Scan the RF environment, Coordinate intermod-free frequencies in software, Program every transmitter and receiver, Walk-test each channel across the whole stage, Label everything and chart it, and program Backup frequencies for in-show interference.
Skipping the scan or the walk-test is where show-stopping wireless failures come from.
In practice: Two hours before doors for a band needing seven wireless channels: scan, coordinate seven plus backups, program, walk-test, label, post the frequency chart.
Wireless setup: scan → coordinate → program → walk-test → label → backup.
6
Wireless Dropout Causes: Multipath, Interference, and Body Blocking
Wireless dropouts come from five recognizable causes: multipath (reflections cancelling the signal), excess distance, interference from other RF, low battery cutting transmit power, and the performer's own body blocking the transmitter antenna.
Knowing the five lets you diagnose fast, and most are prevented up front by diversity reception and good antenna placement.
In practice: A singer who drops out only when she faces stage left: that is body blocking, her body is between the handheld's antenna and the receiver. Reposition or widen the antennas.
Five dropout causes: multipath, distance, interference, battery, body blocking.
7
Battery Management: Voltage Curves, Monitoring, and Swap Timing
Transmitter batteries are a show-reliability issue, and disposable alkalines are the trap, their voltage curve is unpredictable, so a meter can read half-full and die twenty minutes later. Intelligent rechargeable systems communicate real runtime in hours and minutes.
Whatever the battery type, the discipline is the same: fresh batteries at the top of every set, a tracked system for charged vs. used, and backups on hand.
In practice: A mic dying mid-set on alkalines: switch to a rechargeable system with true runtime display, or at minimum put fresh batteries in at every set break regardless of the meter.
Alkaline meters lie, use intelligent rechargeables or swap fresh every set.
8
In-Ear Monitor RF: Power, Squelch, and Mic Interaction
IEM RF runs the opposite direction from a wireless mic. A mic transmits from the stage to a receiver at FOH; an IEM transmits from the rack to a bodypack receiver on the performer. So IEM transmitters run higher power to push through the body blocking on the receive side, though the ceiling is a licensing question rather than a hardware one: 50 mW unlicensed under Part 15, and the higher settings your transmitter offers are Part 74 power that assumes you hold the licence.
That higher power makes intermod worse, and an IEM dropout is more dangerous than a mic dropout, because a burst of RF noise straight into a performer's ears can injure hearing. Set squelch carefully.
In practice: Adding IEM transmitters to a clean 3-mic rig and a mic channel starts buzzing: the higher-power IEMs create intermod, re-coordinate all five frequencies as one group.
IEM RF flows rack-to-performer at higher power, re-coordinate everything, set squelch carefully.
9
Systematic Wireless Troubleshooting
Wireless troubleshooting has a strict priority order, and the first rule is: during a show, do not troubleshoot, swap to a backup immediately, because audio to the PA comes first. Only after that do you diagnose: battery first (the most common cause), then antenna connections, then the receiver's RF meter, then scan for interference, then try a backup frequency.
A useful tell: strong RF but bad audio means the problem is in the audio chain, cable, connector, capsule, not the RF link.
In practice: A handheld goes silent mid-song: grab the wired backup mic for the performer first, then check the receiver, no RF means battery/transmitter, strong RF means the audio chain.
Wireless failure mid-show: swap to backup first, then diagnose battery → antenna → RF → interference.
These lessons are the teach side of knowledge cards from the Live Sound deck. In the daily plan each one is followed by a quiz, spaced over weeks, so it stays known rather than read once.