Section 15.236 - Operation of wireless microphones in the bands 54-72 MHz, 76-88 MHz, 174-216 MHz, 470-608 MHz, 614-616 MHz and 657-663 MHz(a)Definitions. The following definitions apply in this section. 600 MHz duplex gap. An 11 megahertz guard band at 652-663 MHz that separates part 27 600 MHz service uplink and downlink frequencies.
600 MHz guard band. Designated frequency band at 614-617 MHz that prevents interference between licensed services in the 600 MHz service band and channel 37.
Wireless Microphone. An intentional radiator that converts sound into electrical audio signals that are transmitted using radio signals to a receiver which converts the radio signals back into audio signals that are sent through a sound recording or amplifying system. Wireless microphones may be used for cue and control communications and synchronization of TV camera signals as defined in § 74.801 of this chapter. Wireless microphones do not include auditory assistance devices as defined in § 15.3(a) of this part.
Wireless multichannel audio systems. Wireless audio transmission systems using broadband digital transmission techniques for microphone and in-ear monitor system applications and other multichannel audio use.
(b)Permissible operations. Operation under this section is limited to wireless microphones and wireless multichannel audio systems as defined in this section.(c)Frequency bands. Operation of wireless microphones is permitted in all of the following frequency bands. Wireless multichannel audio systems may operate only in the bands listed in paragraphs (c)(1) and (2) of this section.(1) Channels allocated and assigned for the broadcast television service.(2) The 657-663 MHz segment of the 600 MHz duplex gap.(3) The 614-616 MHz segment of the 600 MHz guard band.(d)Power limits. The maximum radiated power shall not exceed the following values: (1) In the bands allocated and assigned for broadcast television:(i) Wireless microphones: 50 mW EIRP.(ii) Wireless multichannel audio systems with a bandwidth up to 1 MHz: 50 mW EIRP.(iii) Wireless multichannel audio systems with a bandwidth greater than 1 MHz: 100 mW EIRP.(2) In the 600 MHz guard band and the 600 MHz duplex gap: 20 mW EIRP.(e)Operating locations. Operation is limited to locations at least four kilometers outside the following protected service contours of co-channel TV stations: Table 1 to Paragraph (e)
| Type of station | Protected contour |
| Channel | Contour (dBu) | Propagation curve |
| Digital: Full service TV, Class A TV, LPTV, translator and booster | Low VHF (2-6) | 28 | F(50,90) |
| High VHF (7-13) | 36 | F(50,90) |
| UHF (14-36) | 41 | F(50,90) |
(f)Operating frequency and bandwidth -(1)Wireless microphones. The operating frequency within a permissible band of operation defined in paragraph (c) of this section must comply with the following requirements.(i) The frequency selection shall be offset from the upper or lower band limits by 25 kHz or an integral multiple thereof.(ii) One or more adjacent 25 kHz segments within the assignable frequencies may be combined to form a channel whose maximum bandwidth shall not exceed 200 kHz. The operating bandwidth shall not exceed 200 kHz.(iii) The frequency tolerance of the carrier signal shall be maintained within ±0.005% of the operating frequency over a temperature variation of -20 degrees to +50 degrees C at normal supply voltage, and for a variation in the primary supply voltage from 85% to 115% of the rated supply voltage at a temperature of 20 degrees C. Battery operated equipment shall be tested using a new battery. (2)Wireless multichannel audio systems. A wireless multichannel audio system may have an operating bandwidth not exceeding 6 megahertz and must have a mode of operation in which it is capable of operating with at least three audio channels per megahertz. For wireless multichannel audio systems operating in the TV bands (channels 2-36), the 6 megahertz (or less) channel must fall entirely within a single TV channel.(g)Emission masks -(1)Analog systems. Emissions within the band from 2.5 * B below to 2.5 * B above the carrier frequency, where B is the channel bandwidth, shall comply with the emission mask in Figure 1 of section 4.2.4.2.2 of ETSI EN 300 422-1 V2.2.1 (2021-11) (incorporated by reference, see § 15.38 ).(2)Digital systems. Emissions within the band from 2.5 * B below to 2.5 * B above the carrier frequency, where B is the channel bandwidth, shall comply with the emission mask in Figure 2 of section 4.2.4.2.2 of ETSI EN 300 422-1 V2.2.1 (2021-11) (incorporated by reference, see § 15.38 ).(3)Wireless Multichannel Audio Systems. Emissions within the band from 2.5 * B below to 2.5 * B above the carrier frequency, where B is the channel bandwidth, shall comply with the emission mask in Figure 3 of section 4.2.4.2.2 of ETSI EN 300 422-1 V2.2.1 (2021-11), (incorporated by reference, see § 15.38 ).(4)Spurious emission limits. Emissions outside of the emission masks listed in paragraphs (g)(1) through (g)(3) shall comply with the limits specified in section 4.2.4.1.2 of ETSI EN 300 422-1 V2.2.1 (2021-11), (incorporated by reference, see § 15.38 ). 80 FR 73069 , Nov. 23, 2015, as amended at 81 FR 4974 , Jan. 29, 2016; 82 FR 41559 , Sept. 1, 2017 As amended at 81 FR 4974 , 1/29/2016; 82 FR 41559 , 10/2/2017; 89 FR 83798 , 11/18/2024