User:Thornfield Hall/Radio

GMRS Frequency table

 * Table notes:(1) Shared FRS and GMRS simplex. (2) Shared FRS and GMRS simplex; GMRS repeater output. (3) GMRS repeater input. The output frequency of this repeater input is the input frequency minus 5 MHz. (4) FRS transmissions are limited to 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. (7) National GMRS calling channel (CTCSS tone 141.3 Hz).

Marine VHF
A marine VHF set is a combined transmitter and receiver and only operates on standard, international frequencies known as channels. Channel 16 (156.8 MHz) is the international calling and distress channel. Transmission power ranges between 1 and 25 watts, giving a maximum range of up to about 60 nautical miles (111 km) between aerials mounted on tall ships and hills, and 5 nmi between aerials mounted on small boats at sea level. Frequency modulation (FM) is used, with vertical polarization, meaning that antennas have to be vertical in order to have good reception. For longer range communication at sea, marine MF and marine HF bands and satellite phones can be used.

Half-duplex channels here are listed with the A and B frequencies the same. The frequencies, channels, and some of their purposes are governed by the ITU. For an authoritative list see. The original allocation of channels consisted of only channels 1 to 28 with 50 kHz spacing between channels, and the second frequency for full-duplex operation 4.6 MHz higher.

Improvements in radio technology later meant that the channel spacing could be reduced to 25 kHz with channels 60 to 88 interspersed between the original channels.

Channels 75 and 76 are omitted as they are either side of the calling and distress channel 16, acting as guard channels. The frequencies which would have been the second frequencies on half-duplex channels are not used for marine purposes and can be used for other purposes that vary by country. For example, 161.000 to 161.450 MHz are part of the allocation to the  Association of American Railroads channels used by railways in the US and Canada.