Legal bands
The 614 to 616 MHz Duplex Gap
Quick answer
The 614 to 616 MHz duplex gap is legal for unlicensed wireless microphones at a 20 mW power limit. It is only 2 MHz wide, which is perhaps two or three channels, and the low power ceiling costs roughly half the range of a 50 mW channel in the UHF band below.
When the 600 MHz band was auctioned, a narrow sliver was left open for wireless microphones directly above the prohibited television channel 37. That sliver is this page. It is real, it is legal, and it is small: two megahertz, at a fifth of the power allowed in the main UHF working band. It is worth knowing about because it is genuinely useful for one or two short-range channels, and worth being honest about because no church should plan a system around it. Work out how many channels you actually need in the wireless microphone channel calculator first.
What the 20 mW limit costs you in range
Power and distance are related by a simple rule: every 6 dB of power change halves or doubles the free field distance at which a given signal strength arrives. Going from 50 mW to 20 mW is a factor of 2.5, which is about 4 dB, so the honest expectation is roughly two thirds of the distance rather than half. In a real building with a body between the transmitter and the receiver it is worse than that, because the margin you just gave away was the margin absorbing the obstacles.
At 20 mW the duplex gap gives roughly two thirds of the line of sight range of a 50 mW unlicensed UHF channel, before any obstacle is accounted for.
| Where you are operating | Power ceiling | Relative to 50 mW | Realistic indoor range |
|---|---|---|---|
| Part 74 licensed, UHF TV band | 250 mW | About 7 dB more | 300 feet and beyond |
| Unlicensed, UHF TV band | 50 mW | Reference | 200 to 300 feet |
| Unlicensed, 614 to 616 MHz guard band | 20 mW | About 4 dB less | 130 to 200 feet |
Range figures are practical expectations from published manufacturer line of sight specifications reduced for a typical building. A person standing between a body pack and a receiver antenna costs more than the whole power difference in this table.
How many channels really fit in 2 MHz?
Two megahertz is a third of one television channel, so the density arithmetic from the main band scales straight down. At the 400 kHz minimum spacing an analog system needs, two megahertz is one or two channels once you leave room at the edges. A digital system at 250 kHz spacing manages two or three. Nobody is running a band here.
The duplex gap holds about two or three channels in a digital system and one or two in an analog one.
| Mode | Minimum spacing | Channels in 2 MHz | Suitable for |
|---|---|---|---|
| Analog | 400 kHz | 1 to 2 | A single short range spare |
| Digital | 250 kHz | 2 to 3 | A lectern channel and a spare capsule |
| High-density digital mode | 125 kHz | 3 to 4 in theory | Rarely offered here by manufacturers |
Manufacturer support matters more than arithmetic. Not every system can tune into this segment at all, and those that can may restrict power automatically, which is the behaviour you want.
When the duplex gap is genuinely the right answer
There is one situation where this sliver earns its place: a short throw channel in a crowded market where every television channel below 608 MHz is already spoken for. A lectern microphone with a body pack twenty feet from its receiver does not need 50 mW, and putting it up here frees a frequency in the main band for a roaming handheld that does. The same logic applies to a fixed communion table microphone or a choir director channel that never leaves the platform.
What it is not is a place to put the preacher. A roaming preaching channel is the one transmitter in the building that must never drop, it moves the furthest from the receiver, and it spends a good deal of its life with a human body between the antenna and the rack. Give that channel the power. For the reasoning behind position by position choices, see the microphone for a preaching pastor and the pulpit and lectern.
Systems that can use it, and the safer default
Support for this segment varies by manufacturer and by product generation, so the tuning range printed on the receiver is the only thing worth trusting. For most churches the sensible default is to stay in the main UHF band and reach for a digital system when density gets tight, rather than to chase two extra channels at a fifth of the power.
Shure SLXD24/SM58 Digital Wireless Microphone System - Includes SLXD2 Handheld Transmitter with SM58 Vocal Mic Capsule and SLXD4 Single Channel Rack Mount Receiver
$769.00 Specs and sizingDigital transmission doubles what fits in each open television channel below 608 MHz, which solves the same crowding problem the duplex gap is usually reached for, at full unlicensed power.
Best for: A church that has run out of room in the main band
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Shure GLXD24+/SM58 Digital Wireless Vocal System - Z3 Band
$659.00 Specs and sizingDual band 2.4 and 5.8 GHz with automatic frequency management, so a crowded UHF market stops being your problem at all. Range is about 100 feet and it shares spectrum with the building network.
Best for: Small rooms in markets where every TV channel is occupied
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Sennheiser Pro Audio EW-D 835-S Wireless Handheld Microphone System, R1-R6
$699.00 Specs and sizingA 56 MHz tuning range gives a coordinator somewhere to go when the plan breaks, which is a better answer to crowding than a 2 MHz sliver at reduced power.
Best for: Churches near a broadcast tower with several channels to place
Check price on AmazonHow we chose
We did not test these products in person and we never claim to. Picks are researched from manufacturer specification sheets and operator manuals, FCC rules where spectrum is involved, published standards, warranty terms, and the recurring themes in verified owner reviews. Every pick is matched to a real room size, seat count or input list rather than to a price bracket, and it is placed in the tier where its capability actually belongs. Where a product is wrong for most churches we say so on the page.
Sources
- FCC guidance for wireless microphone users
- FCC Part 15 rules for low power wireless microphones in the TV bands and duplex gap
- Published manufacturer tuning range specifications for current Shure and Sennheiser wireless platforms
Frequently asked questions
Is the 614 to 616 MHz guard band legal for churches?
Yes, for unlicensed operation at up to 20 mW. It is one of the few places above the main UHF band where a wireless microphone may still transmit, and it was deliberately preserved when the surrounding spectrum was auctioned. The limits are the power ceiling and the width: two megahertz is two or three channels at most, not a system.
How much range do I lose at 20 mW?
Roughly a third compared with a 50 mW unlicensed channel in the UHF band, before obstacles. The power ratio is about 4 dB, and free field distance changes by half for every 6 dB. In a real room with a body between the transmitter and the receiver antenna the practical loss is larger, so treat this segment as short throw spectrum.
Which channels should I put in the duplex gap?
Fixed, short throw positions. A lectern body pack, a communion table microphone or a choir director channel all sit close to the receiver and never move. Keep the roaming preaching channel and any handheld that travels into the congregation in the main UHF band, where the extra power buys the margin those positions actually need.
Will my existing wireless system tune into 614 to 616 MHz?
Only if its printed tuning range covers it, and support varies by manufacturer and product generation. Do not assume a system reaches this segment because its band letter looks close. Read the megahertz range on the receiver, and prefer a system that reduces power automatically when tuned here rather than one that leaves it to you.
Can I get more channels by spacing them closer together?
Not safely with analog systems. Analog transmitters generate intermodulation products, chiefly at twice one frequency minus another, and those products behave like extra transmitters inside the band. The 400 kHz minimum spacing exists to keep them from landing on a working channel. Digital systems tolerate 250 kHz, which is why they fit more in the same sliver.
Is it worth buying a system specifically for the duplex gap?
No. Buy a system for the main 470 to 608 MHz band and treat the duplex gap as a bonus if your chosen platform happens to reach it. Two channels at reduced power is not a reason to narrow your shortlist, and a digital system in the main band solves the same crowding problem with better range and more room to grow.
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.