Portable and pack radio sets must be lightweight, compact, and self-contained. Usually, these sets are
powered by a battery or a hand generator, have low output power, and are either transceivers or
transmitter-receivers. A transceiver consists of a transmitter and a receiver that share common circuits and
are housed in the same case or cabinet. A transmitter-receiver is the combination of two separate pieces of
equipment that are used together. Navy ships carry a variety of these radio sets for emergency and
amphibious communications. The numbers and types of equipment vary according to the individual ship.
One piece of emergency equipment is shown in figure 5-14. It is a rugged emergency transmitter
carried aboard ships and aircraft for use in lifeboats and life rafts. The transmitter operates on the
international distress frequency (500 kilohertz) and the survival craft communications frequency (8,364
Figure 5-14.Typical emergency lifeboat transmitter.
The complete radio transmitter, including the power supply, is contained in an aluminum cabinet that
is airtight and waterproof. The cabinet is shaped to fit between the legs of the operator and has a strap for
securing it in the operating position.
The only operating controls are a three-position selector switch and a push-button telegraph key. A
hand crank screws into a socket in the top of the cabinet. The generator, automatic keying, and automatic
frequency changing are all operated by turning the hand crank. While the hand crank is being turned, the
set automatically transmits the distress signal SOS in Morse code. The code consists of six groups of SOS
followed by a 20-second dash. It is transmitted alternately on 500 kilohertz and 8,364 kilohertz. The
frequency automatically changes every 50 seconds. These signals are intended for reception by two
groups of stations, each having distinct rescue functions. Direction-finding stations cooperating in long-
range rescue operations normally use 8,364 kilohertz, whereas aircraft or ships locally engaged in search
and rescue missions use 500 kilohertz.
Besides the automatic feature, you can key the transmitter manually on 500 kilohertz only. This is
done by means of a push-button telegraph key.