Wireless
How to Coordinate Wireless Microphone Frequencies
Quick answer
Eight digital wireless channels fit in a single 6 MHz TV channel, so one open TV channel covers most churches, while analog systems fit only four. Work inside 470 to 608 MHz, keep at least 250 kHz between digital channels, and never operate in 617 to 652 or 663 to 698 MHz.
Coordination is the reason one church runs ten wireless channels flawlessly and another gets a burst of static on the pastor's headset every third Sunday. It is not luck and it is not brand. It is whether the frequencies chosen are inside legal spectrum, inside TV channels that are empty where your building stands, and spaced far enough apart that the radios do not generate interference with each other.
The arithmetic is small. A US TV channel is 6 MHz wide. A digital system needs about 250 kHz of spacing, so eight fit comfortably. An analog system needs about 400 kHz and generates more intermodulation products, so four is the realistic figure. High-density modes on some digital platforms get to fifteen. Put your channel count into the wireless microphone channel calculator and it will tell you how many open TV channels you need to find.
On this page
How many channels fit in the spectrum you have?
Capacity is the number of empty TV channels at your location multiplied by how many microphones fit in each one. Everything else in coordination is detail. Find your open channels first, then count.
Two open TV channels carry 16 digital wireless channels but only 8 analog ones, which is why analog systems run out of room first in a growing church.
| Open TV channels | Analog UHF, 4 per channel | Digital UHF, 8 per channel | High-density mode, 15 per channel |
|---|---|---|---|
| 1 open channel | 4 | 8 | 15 |
| 2 open channels | 8 | 16 | 30 |
| 3 open channels | 12 | 24 | 45 |
| 4 open channels | 16 | 32 | 60 |
| 6 open channels | 24 | 48 | 90 |
| 8 open channels | 32 | 64 | 120 |
Minimum spacing is about 400 kHz for analog, 250 kHz for standard digital and 125 kHz in a high-density mode. These are realistic working figures, not a manufacturer best case measured in an empty field. In a dense urban market with few vacant TV channels, the left-hand column is what limits you, not the gear.
Coordinating a system, step by step
- Find the vacant TV channels at your address. Use the FCC TV query tool or your manufacturer coordination software with your exact street address, not the city. Vacant channels change across a metropolitan area, and a church five miles from another can have a completely different list.
- Count what you need, then add spares. List every transmitter: handhelds, lavaliers, headsets, in-ear packs and any wireless instrument system. The convention is one spare transmitter per four channels in service, so eight channels means two spares, and the spares need frequencies too.
- Let the manufacturer software pick the frequencies. Scan the room with the receivers, feed the scan into the coordination software and let it calculate a compatible group. It is solving for intermodulation products, which are new frequencies created when two transmitters mix, and no human does that arithmetic by hand for ten channels.
- Keep the transmitters apart from each other. Two body packs sitting side by side on a table generate the strongest intermodulation you will ever see. Keep transmitters at least a few feet apart in use, and store them switched off rather than parked next to the receiver rack.
- Get the antennas in line of sight. Put receiver antennas where they can see the platform, not inside a metal rack behind a door. If the rack is remote, use a proper antenna distribution system and low-loss coaxial cable, and remember that every splitter and every foot of thin coax costs signal.
- Walk the whole room before you trust it. Walk every part of the platform, the aisles, the back of the room and anywhere a roaming microphone goes, listening to the receiver output on headphones. You are looking for the dead spot behind a steel column that no scan will predict.
- Write the frequencies down and lock them. Record every frequency, group and channel on paper in the rack and in the church files. Lock the transmitters and receivers so a volunteer cannot change a channel by accident, because a single rescan on a Sunday morning can break a coordinated group.
Why analog and digital are not interchangeable here
An analog UHF system transmits a frequency-modulated carrier that spreads, and when two carriers mix in a receiver front end they generate third-order products at twice the first frequency minus the second. Those products land on real frequencies and sound exactly like interference. Guard bands are the defence, which is why analog practice puts 400 kHz between channels and why four per TV channel is the honest figure.
A digital system such as Shure SLXD24/SM58 Digital Wireless Microphone System - Includes SLXD2 Handheld Transmitter with SM58 Vocal Mic Capsule and SLXD4 Single Channel Rack Mount Receiver or Sennheiser Pro Audio EW-D 835-S Wireless Handheld Microphone System, R1-R6 transmits a tightly bounded digital signal that behaves far better in company, so 250 kHz of spacing is workable and eight fit in a TV channel. Digital systems also fail differently: instead of gradually hissing, they hold perfectly and then mute, which is easier to notice in a rehearsal and more alarming in a service. The trade-off is argued in full at analog versus digital wireless microphones.
For a church running two to four channels, either works and analog systems such as Shure BLX24/SM58 Wireless Microphone System - 14-Hour Battery Life, 300 ft Range, UHF save real money. Past about six channels, or in a market with few vacant TV channels, digital is the only path that scales. Both are compared for church use in best wireless microphones for churches.
The 2.4 GHz option, and where it stops working
Systems in the 2.4 GHz ISM band such as Shure GLXD24+/SM58 Digital Wireless Vocal System - Z3 Band avoid the TV spectrum question entirely. They are unlicensed, legal everywhere in the US, and they coordinate themselves. For a church plant, a portable rig or a two-channel setup, that is a genuinely good answer and it removes the hardest part of this page.
The limit is that 2.4 GHz is shared with every Wi-Fi access point in the building, every phone hotspot in the congregation and the guest network you just installed for the livestream. Channel counts are modest, range is shorter, and the band gets busier every year. If you go this route, plan the Wi-Fi around the microphones rather than the other way round: park the access points on 5 GHz where possible and keep the 2.4 GHz network on a channel plan that leaves room. The comparison is at UHF versus 2.4 GHz wireless microphones, and the band itself is described at 2.4 GHz ISM.
Antennas, cable and the things that cause Sunday dropouts
Most dropouts blamed on coordination are antenna problems. A receiver with its stock quarter-wave antennas inside a closed metal rack is listening through a shield. The fix is either to move the receivers where they can see the platform, or to run remote antennas on the wall with an antenna distribution amplifier feeding the whole rack from one pair.
Coaxial cable loss rises with frequency and it is significant at 600 MHz: thin RG-58 loses several decibels over 50 feet, which is signal you cannot get back. Use the low-loss cable the manufacturer specifies and keep runs as short as the layout allows. Antenna placement matters more than antenna gain: a paddle antenna pointed at the platform from 20 feet away beats a high-gain antenna pointed at a wall.
Diversity receivers use two antennas to pick whichever is receiving better at that instant, which defeats the dropout caused by a reflection cancelling the direct signal at one exact spot. Keep the two antennas separated by at least a quarter wavelength, which at 600 MHz is about 5 inches, and angled apart rather than parallel. Rack layout for all of this is in church AV rack planning.
Batteries are the recurring cost nobody budgets
Six transmitters in service need six charged packs plus six spares, so twelve packs in rotation, and a schedule of three services or rehearsals a week at three hours each is nine hours a week, which is two charge cycles. On alkaline cells instead, six transmitters at two cells each across three services a week is 1,872 cells a year. At typical bulk pricing that is a meaningful four-figure annual line, and it is the cost that makes rechargeable systems pay for themselves inside two years.
Work your own numbers with the wireless battery budget calculator. The other half of the answer is discipline: fresh packs before every service, no exceptions, and a labelled charging station so nobody has to guess which pack came off which transmitter. A dying battery produces exactly the symptoms people blame on coordination.
Sources
- FCC, Wireless Microphones
- FCC rules for unlicensed wireless microphones, 47 CFR 15.236
- Channel density and spacing figures as implemented in src/lib/avmath.mjs
Frequently asked questions
How many wireless microphones can a church realistically run?
It depends on how many TV channels are vacant at your address. Each vacant 6 MHz channel holds about four analog systems, eight standard digital ones or fifteen in a high-density digital mode. A church with four open TV channels can run 32 digital channels, which is far more than most need. In a dense market with one open channel, eight is the ceiling.
Do I need coordination software for four microphones?
Not necessarily. Four channels from one manufacturer, set to a factory group that is designed to be intermodulation free, will usually work if that group sits in a vacant TV channel. The moment you mix brands, exceed about six channels or add in-ear transmitters, run the manufacturer software. Mixed-brand systems are where hand-picked frequencies most often fail.
Why does the system work in rehearsal and fail on Sunday?
Usually because the room is full. Bodies absorb UHF energy, so the signal arriving at the receiver is weaker with a congregation present than in an empty room. Add more transmitters switched on at once, phones on every lap and a battery that was fine two hours ago, and a marginal system tips over. Improve antenna placement and battery discipline before rescanning frequencies.
Can I use the 614 to 616 MHz guard band?
Yes, at up to 20 milliwatts, which is a quarter of the power allowed elsewhere in the TV band. It is a 2 MHz sliver, so realistically it holds two or three channels at reduced range. It is useful as an overflow for a couple of extra bodypacks in a small room, not as the backbone of a church system.
Does a licence make coordination easier?
A Part 74 licence raises your permitted power from 50 to 250 milliwatts in the UHF TV band and gives you standing to register for protection at large events, but eligibility generally requires routinely using 50 or more wireless microphones, which excludes almost every church. It does not create spectrum. Coordination is still the same exercise of finding vacant TV channels and spacing channels properly.
How many spare transmitters should we own?
One spare for every four channels in service, and the spares need coordinated frequencies programmed before the service, not during it. A church running eight channels keeps two spares charged, tested and labelled. A spare that has to be scanned and coordinated in the five minutes before a service is not a spare, it is a second problem.
Researched, not professional advice. This page is compiled from published manufacturer specifications, operator manuals, FCC rules, published standards and owner-review consensus, not hands-on testing. Sound system design, rigging loudspeakers overhead, and any electrical work are jobs for a qualified professional: have flown loudspeakers and their attachment points signed off by a structural engineer or a certified rigger, and have all wiring done by a licensed electrician to your local code. Wireless microphone rules change, so confirm the current FCC position before buying. As an Amazon Associate we earn from qualifying purchases.