From 1965 "Shipboard Radio Equipment"

Transmitter-Receiver AN/GRC-27( )
    The AN/GRC-27( ), shown in figure 3-13, is a UHF transmitter-receiver set covering frequencies from 225 to 400 mc. This equipment is used for radiotelephone and MCW communications from ship-to-ship, ship-to-shore, or with aircraft. The AN/GRC-27( ) is installed principally in carriers and antisubmarine warfare ships, whose primary missions involve the control of aircraft.

    The transmitter has a power output of 100 watts. It has three crystal-controlled oscillators, using a total of 38 crystals. These crystals, located within the transmitter, do not require handling by the operator. From the combination and multiplication of these 38 crystal frequencies are produced 1750 frequencies spaced at 100-kc intervals throughout the transmitter's frequency range. Any 10 of these 1750 frequencies can be preset manually with selector switch dials. Of the 10 preset frequencies, one then can be selected automatically by a telephone-type dial. The automatic selection can be made either locally at the transmitter or from a remote unit at other locations, such as CIC and the bridge. Only 2 to 7 seconds are required to shift automatically from one channel to another in any of the 10 preset channels.

    The receiver also operates on any of the 1750 channels It is a triple-conversion superheterodyne and has crystal oscillators using 38 crystals in a system separate from but similar to that used in the transmitter. Here, again, automatic shifting of channels is done in about 2 to - 7 seconds.

    Both transmitter and receiver use the same antenna A relay switches the antenna from one to the other.