When did WMAS become legal in the US?

The FCC adopted and released FCC 24-22 on February 15, 2024, it was published in the Federal Register on October 18, 2024 at 89 FR 83789, and the rules became effective on November 18, 2024. WMAS is authorised on both a licensed Part 74 basis and an unlicensed Part 15 basis.

How much bandwidth can a WMAS system use?

Licensed WMAS may use up to 6 MHz in the TV bands and the 600 MHz duplex gap, and up to 20 MHz in 941.5–959.85 MHz, 1435–1525 MHz, 6875–6900 MHz and 7100–7125 MHz. Unlicensed WMAS is capped at 6 MHz and is permitted only in TV channels 2–36 and 657–663 MHz.

Does WMAS give wireless microphones any new spectrum?

No. WMAS operates in the bands wireless microphones already had, at the same power ceilings, and it does not change the July 13, 2020 cutoff for the 600 MHz service band or the prohibition on TV channel 37. It is a spectral efficiency measure, not a spectrum grant.

Do WMAS systems have a minimum channel density requirement?

Yes. WMAS equipment must have an operating mode delivering at least 3 audio channels per MHz, so a 6 MHz carrier must be capable of at least 18 audio channels in some mode. New equipment certifications are also held to the ETSI EN 300 422-1 V2.2.1 (2021-11) emission mask.

Rules & licensing

WMAS, explained: the new wideband wireless standard

RF ScoutUpdated July 26, 20265 min read

WMAS — Wireless Multichannel Audio Systems — is a device class the FCC created in FCC 24-22, adopted February 15, 2024 and effective November 18, 2024, covering wireless audio systems that use broadband digital transmission to carry many microphone and in-ear monitor channels inside a single wide RF carrier instead of one narrow carrier per channel. Licensed WMAS may occupy up to 6 MHz in the TV bands and duplex gap and up to 20 MHz in the other Part 74 bands; unlicensed WMAS is limited to TV channels 2–36 plus 657–663 MHz at up to 6 MHz. Crucially, WMAS opens no new spectrum — it is a more efficient way to use the bands wireless microphones already have.

WMAS is the first genuinely new thing to happen to US wireless microphone rules since the repack took the top of the band away. Most of what has been written about it is either a manufacturer press release or a paragraph of spec sheet. Here is the plain version.

What WMAS is

Conventional wireless microphones are narrowband: each transmitter occupies a slice on the order of 200 kHz, and a coordinated system is a set of individual carriers spaced apart far enough that their intermodulation products do not land on each other. Channel count is limited less by raw spectrum than by the spacing arithmetic — see intermodulation, explained for why.

WMAS inverts that. One wide RF carrier — up to 6 MHz, the width of a TV channel — carries many audio channels inside it as a single digital transmission, with the system managing the allocation internally. There are no intermod products between channels that share a carrier, because they are not separate carriers. The FCC's own framing is a device class for "wireless audio transmission systems using broadband digital transmission techniques for microphone and in-ear monitor system applications and other multichannel audio use."

What the FCC actually did, and when

Proceeding: ET Docket 21-115, originating from petition RM-11821.
Order: FCC 24-22, adopted and released February 15, 2024.
Federal Register: Published October 18, 2024 at 89 FR 83789.
Effective: November 18, 2024. WMAS is live rule, not a proposal.

The order creates WMAS on both a licensed basis under Part 74 and an unlicensed basis under Part 15. The two versions are not the same animal, and the difference is larger than the usual power gap.

Licensed WMAS

Bands	Max WMAS bandwidth	Power
TV bands and the 600 MHz duplex gap	6 MHz	Same ceilings as existing narrowband LPAS
941.5–959.85, 1435–1525, 6875–6900, 7100–7125 MHz	20 MHz	Same ceilings as existing narrowband LPAS

Licensed WMAS operates in the same bands narrowband licensed gear already had, at the same power ceilings. Nothing was added and nothing was taken away — the change is that a licensee may now put a 6 MHz wide signal where previously it had to place a comb of narrow ones. Eligibility is unchanged too: you still need to qualify under §74.832(a). See do you need an FCC license.

Unlicensed WMAS

Permitted only in TV channels 2 through 36 and the 657–663 MHz duplex gap segment. Not the 614–616 MHz guard band.
Maximum bandwidth 6 MHz.
Power no greater than two narrowband unlicensed wireless microphones combined — widely reported as 100 mW EIRP.

The efficiency string attached

The Commission did not hand out 6 MHz carriers for free. WMAS equipment must have an operating mode that delivers at least 3 audio channels per MHz. In other words, a 6 MHz WMAS carrier has to be capable of carrying at least 18 audio channels in some mode, or it does not qualify. The requirement exists precisely to stop WMAS being used as a way to occupy a whole TV channel with a handful of links.

New equipment certifications are also held to a new emission mask standard: ETSI EN 300 422-1 V2.2.1 (2021-11). That is the European harmonised standard for wireless audio, which is a quiet but significant piece of transatlantic alignment — it lowers the cost of building one radio for both markets.

What WMAS does not do

If the band at your location is full of repacked television stations, WMAS does not help you find a hole — it helps you get more channels out of a hole once you have found one. The scarce resource is still vacant TV channels at a specific address, which is still worth checking before the truck rolls. See the 600 MHz repack and why channel 37 is off limits.

Is there anything to buy?

Yes. Shure announced Axient Digital PSM on October 22, 2024 as the first WMAS product, shipping in early 2025, with a claim of 28 channels per 6 MHz in the US. Sennheiser has a WMAS programme of its own. This is in-ear monitoring and large-format live territory first, which is the natural fit: the value of WMAS scales with channel count, and it is at forty and eighty channels that narrowband coordination becomes genuinely painful.

Should a bag mixer care yet?

Honestly, not much, not yet. If you are running six to twelve channels out of a cart or a bag, narrowband coordination inside 470–608 MHz still works fine and your existing gear is not obsolete. WMAS matters when the channel count is high enough that intermod maths, not spectrum, is your binding constraint — festivals, theatre, large-scale broadcast, corporate general sessions.

The medium-term reason to pay attention is different: a rule that lets a system carry 28 channels in one TV channel changes what "the band is full" means. Over the next few years the mixers who understand WMAS bandwidth planning will be the ones who can still say yes to a hundred-channel show in a bad market.

Narrowband or wideband, it starts with knowing which TV channels are actually vacant where you are shooting.

See what is open at your location

Common questions

What is WMAS?: WMAS stands for Wireless Multichannel Audio Systems — a device class the FCC created for wireless audio systems that use broadband digital transmission to carry many microphone and in-ear monitor channels within a single wide RF carrier, rather than one narrowband carrier per channel. It was authorised in FCC 24-22 and the rules took effect on November 18, 2024.
When did WMAS become legal in the US?: The FCC adopted and released FCC 24-22 on February 15, 2024, it was published in the Federal Register on October 18, 2024 at 89 FR 83789, and the rules became effective on November 18, 2024. WMAS is authorised on both a licensed Part 74 basis and an unlicensed Part 15 basis.
How much bandwidth can a WMAS system use?: Licensed WMAS may use up to 6 MHz in the TV bands and the 600 MHz duplex gap, and up to 20 MHz in 941.5–959.85 MHz, 1435–1525 MHz, 6875–6900 MHz and 7100–7125 MHz. Unlicensed WMAS is capped at 6 MHz and is permitted only in TV channels 2–36 and 657–663 MHz.
Does WMAS give wireless microphones any new spectrum?: No. WMAS operates in the bands wireless microphones already had, at the same power ceilings, and it does not change the July 13, 2020 cutoff for the 600 MHz service band or the prohibition on TV channel 37. It is a spectral efficiency measure, not a spectrum grant.
Do WMAS systems have a minimum channel density requirement?: Yes. WMAS equipment must have an operating mode delivering at least 3 audio channels per MHz, so a 6 MHz carrier must be capable of at least 18 audio channels in some mode. New equipment certifications are also held to the ETSI EN 300 422-1 V2.2.1 (2021-11) emission mask.

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.