Courtesy of Wikipedia
GMRS is allotted 30 frequency channels in the vicinity of 462 MHz and 467 MHz. They are divided into 16 main channels and 14 interstitial channels.
Licensees may use the eight main 462 MHz channels for Simplex Communication or “Repeater” outputs.
The eight main 467 MHz channels may only be used as repeater inputs, in conjunction with the 462 MHz channels as repeater outputs. The repeater input frequencies are exclusive to GMRS, and may only be used by licensed GMRS operators.
GMRS operators are permitted to transmit at up to 50 watts, on the 16 main channels, but transmitting 1 to 5 watts is more common in practice.
The interstitial frequencies are in-between the main channels, and they may be used for simplex as long as the “Transmitter Power Output” does not exceed 5 watts. The 467 MHz interstitial frequencies have a power limit of 500 milliwatts ERP, and they may only be used by hand-held portable units.
Sharing with FRS
All 22 Family Radio Service (FRS) frequencies are shared with GMRS, and users of the two services may communicate with each other. With the exception of FRS channels 8 through 14, GMRS licensees may use higher power radios with detachable or external antennas.
FRS and GMRS Frequency Table
| Frequency | FRS Channel | FRS Power | FRS Bandwidth | GMRS Power | GMRS Bandwidth | Notes |
|---|---|---|---|---|---|---|
| 462.5625 MHz | 1 | 2 W | 12.5 kHz | 5 W | 20 kHz | (1)(4)(5) |
| 462.5875 MHz | 2 | 2 W | 12.5 kHz | 5 W | 20 kHz | (1)(4)(5) |
| 462.6125 MHz | 3 | 2 W | 12.5 kHz | 5 W | 20 kHz | (1)(4)(5) |
| 462.6375 MHz | 4 | 2 W | 12.5 kHz | 5 W | 20 kHz | (1)(4)(5) |
| 462.6625 MHz | 5 | 2 W | 12.5 kHz | 5 W | 20 kHz | (1)(4)(5) |
| 462.6875 MHz | 6 | 2 W | 12.5 kHz | 5 W | 20 kHz | (1)(4)(5) |
| 462.7125 MHz | 7 | 2 W | 12.5 kHz | 5 W | 20 kHz | (1)(4)(5) |
| 467.5625 MHz | 8 | 0.5 W | 12.5 kHz | 0.5 W | 12.5 kHz | (1)(4)(6) |
| 467.5875 MHz | 9 | 0.5 W | 12.5 kHz | 0.5 W | 12.5 kHz | (1)(4)(6) |
| 467.6125 MHz | 10 | 0.5 W | 12.5 kHz | 0.5 W | 12.5 kHz | (1)(4)(6) |
| 467.6375 MHz | 11 | 0.5 W | 12.5 kHz | 0.5 W | 12.5 kHz | (1)(4)(6) |
| 467.6625 MHz | 12 | 0.5 W | 12.5 kHz | 0.5 W | 12.5 kHz | (1)(4)(6) |
| 467.6875 MHz | 13 | 0.5 W | 12.5 kHz | 0.5 W | 12.5 kHz | (1)(4)(6) |
| 467.7125 MHz | 14 | 0.5 W | 12.5 kHz | 0.5 W | 12.5 kHz | (1)(4)(6) |
| 462.5500 MHz | 15 | 2 W | 12.5 kHz | 50 W | 20 kHz | (2)(5) |
| 462.5750 MHz | 16 | 2 W | 12.5 kHz | 50 W | 20 kHz | (2)(5) |
| 462.6000 MHz | 17 | 2 W | 12.5 kHz | 50 W | 20 kHz | (2)(5) |
| 462.6250 MHz | 18 | 2 W | 12.5 kHz | 50 W | 20 kHz | (2)(5) |
| 462.6500 MHz | 19 | 2 W | 12.5 kHz | 50 W | 20 kHz | (2)(5) |
| 462.6750 MHz | 20 | 2 W | 12.5 kHz | 50 W | 20 kHz | (2)(5) |
| 462.7000 MHz | 21 | 2 W | 12.5 kHz | 50 W | 20 kHz | (2)(5) |
| 462.7250 MHz | 22 | 2 W | 12.5 kHz | 50 W | 20 kHz | (2)(5) |
| 467.5500 MHz | N/A | N/A | N/A | 50 W | 20 kHz | (3)(5) |
| 467.5750 MHz | N/A | N/A | N/A | 50 W | 20 kHz | (3)(5) |
| 467.6000 MHz | N/A | N/A | N/A | 50 W | 20 kHz | (3)(5) |
| 467.6250 MHz | N/A | N/A | N/A | 50 W | 20 kHz | (3)(5) |
| 467.6500 MHz | N/A | N/A | N/A | 50 W | 20 kHz | (3)(5) |
| 467.6750 MHz | N/A | N/A | N/A | 50 W | 20 kHz | (3)(5) |
| 467.7000 MHz | N/A | N/A | N/A | 50 W | 20 kHz | (3)(5) |
| 467.7250 MHz | N/A | N/A | N/A | 50 W | 20 kHz | (3)(5) |
Table Notes
(1) Shared FRS and GMRS simplex.
(2) Shared FRS and GMRS simplex; GMRS repeater output.
(3) GMRS repeater input.
(4) FRS transmissions are limited to a bandwidth of 11 kHz with a transmitter deviation of +/- 2.5 kHz. Channels are on 12.5 kHz centers.
(5) GMRS transmissions may have a bandwidth of 16 kHz with a transmitter deviation of +/- 5.0 kHz. Channels are on 25 kHz centers.
(6) GMRS transmissions are limited to a bandwidth of 11 kHz with a transmitter deviation of +/- 2.5 kHz. Channels are on 12.5 kHz centers.
Some inexpensive GMRS mobiles and portables do not fully comply with FCC permissible modulation bandwidth for GMRS and thus have weak transmitter audio and reduced range. Not all radios are alike, and typically, you get what you pay for.
Bandwidth vs Channel Spacing Explained
The FCC stipulates a specific channel bandwidth for FRS and GMRS. The bandwidth is constrained by the modulation which is FM deviation (GMRS = +/- 5.0 kHz, FRS = +/- 2.5 kHz) plus the uncertainties of the filtering of the transmitter and receiver. Additionally, receivers and transmitters may drift over time or temperature so the bandwidth is further constrained to prevent interference to the adjacent channel. Channel spacing is 25 kHz for GMRS and so a 20 kHz bandwidth fits into that channel with protection on each side. FRS channels are spaced within a 12.5 kHz space directly between two GMRS channels. FRS radios generally utilize an 11 kHz transmitter bandwidth and a lower power than GMRS so the interference to an adjacent GMRS channel is minimized.
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