Why TV channel 37 is off limits
TV channel 37 — 608–614 MHz — is prohibited for wireless microphones under both licensed and unlicensed rules. It is omitted from the Part 74 frequency list in §74.802(a) and from the unlicensed list in §15.236, and 47 CFR §74.870(c)(2) states plainly that "Operation is prohibited within the 608-614 MHz (TV channel 37) band." The band has been reserved for radio astronomy since an FCC moratorium in 1963, made permanent in 1974, and since 2000 it has also been co-primary with the Wireless Medical Telemetry Service used for hospital patient monitoring.
There is a 6 MHz hole in the middle of the UHF band that no wireless microphone in the United States is allowed to touch. It sits between TV channel 36 and the old channel 38, it never carried a television station anywhere in the country, and on a scan it usually looks like the cleanest spectrum you have ever seen. It is 608–614 MHz, TV channel 37, and it is flatly prohibited.
The rule, in three places
Channel 37 is not merely discouraged or crowded. It is excluded from the frequency list for licensed low power auxiliary stations in §74.802(a), excluded from the unlicensed wireless microphone list in §15.236, and then prohibited again explicitly for good measure.
Reason one: radio astronomy
The FCC put a moratorium on channel 37 assignments in 1963 and made the reservation permanent in 1974. The point was to give radio astronomers a protected window in the UHF range. Astronomy already held allocations near 410 MHz and near 1.4 GHz; channel 37 sits between them and fills in the middle of that observing range.
The band supports very-long-baseline interferometry — observations combined across widely separated dishes, where the sensitivity involved is measured in fractions of a picowatt. A 50 mW body pack is, from that instrument's point of view, a floodlight. This is why the exclusion is national rather than a set of local coordination zones: there is no distance from a radio telescope at which the Commission decided the risk was acceptable enough to write a general rule around it.
Reason two: hospitals
Since 2000, channel 37 has also been co-primary with the Wireless Medical Telemetry Service (WMTS), licensed under 47 CFR Part 95 subpart H. WMTS is what hospitals use for patient telemetry — the wireless cardiac and vital-signs monitoring that follows a patient around a ward.
Why it is a trap on a scan
Channel 37 typically reads as dead silent on a receiver's spectrum scan, and for an obvious reason: nothing there is transmitting at broadcast power. Radio telescopes only receive. WMTS gear is low power and mostly indoors. So a scan-and-deploy workflow that simply picks the quietest window in the band will walk straight into it.
Most current-production receivers exclude channel 37 from their own frequency tables, so a coordination run inside the manufacturer's software will refuse to place you there. Older gear, generic scanners and hand-tuned frequencies will not stop you. If you are working off a raw scan, see scanning and walk-testing for how to read one without trusting it blindly.
Where it sits in the band
| Range | What it is | Wireless mic status |
|---|---|---|
| 470–608 MHz | TV channels 14–36 | Available, licensed and unlicensed |
| 608–614 MHz | TV channel 37 — radio astronomy and WMTS | Prohibited |
| 614–616 MHz | 600 MHz guard band | Unlicensed only, 20 mW EIRP |
| 617–652 MHz | 600 MHz downlink | Prohibited since July 2020 |
| 652–663 MHz | 600 MHz duplex gap | Partly available, 20 mW EIRP |
| 663–698 MHz | 600 MHz uplink | Prohibited since July 2020 |
Worth noticing from that table: channel 37 is now a border, not an island. Before the repack it was a gap in the middle of usable spectrum. Now it marks the ceiling of the band you actually work in. 608 MHz is where the practical UHF band ends, and the 614–616 MHz guard band above it is a 2 MHz afterthought at a twentieth of the power. See the 600 MHz repack, explained for how that came about.
Has any of this changed recently?
No. Nothing in the channel 37 rules moved between 2024 and 2026. The WMAS rulemaking that added wideband wireless audio systems in 2024 did not touch it — WMAS operates in the bands wireless mics already had, and channel 37 was never one of them. See WMAS, explained. Anyone telling you channel 37 has opened up is confusing it with the duplex gap.
RF Scout scores real TV channels at a real address and never hands you one you are not allowed to use.
Get a clean channel listCommon questions
- What frequencies are TV channel 37?
- TV channel 37 occupies 608–614 MHz. No television station has ever been assigned to it in the United States, and it is prohibited for wireless microphone use under both Part 74 licensed rules and Part 15 unlicensed rules.
- Why is TV channel 37 reserved for radio astronomy?
- The FCC imposed a moratorium on channel 37 assignments in 1963 and made the reservation permanent in 1974, to give radio astronomers a protected observing window in the UHF range. It sits between existing astronomy allocations near 410 MHz and 1.4 GHz and supports very-long-baseline interferometry.
- What is WMTS and why does it share channel 37?
- The Wireless Medical Telemetry Service is the licensed service hospitals use for wireless patient monitoring, regulated under 47 CFR Part 95 subpart H. Since 2000 it has been co-primary with radio astronomy in 608–614 MHz, which is a second independent reason wireless microphones are excluded from the band.
- Channel 37 looks completely empty on my scanner. Can I use it?
- No. It reads as empty because radio telescopes only receive and hospital telemetry gear is low power and indoors, not because the band is free. Channel 37 is prohibited by rule regardless of what your scan shows.
Sources
Related notes
Field Notes are general reference, not legal advice or a substitute for the rule text. Spectrum rules change; verify anything you are relying on against the current source before you transmit. See the methodology and disclaimer.