With the exception of three short- range boats, all the Institution's life- boats, both in the active and in the reserve fleet, are equipped with M/F (medium frequency) radio-telephony.

The advantages of a life-boat being in two-way communication with the shore during service are many. The coxswain can be given the latest information about the position and condition of the casualty; he can inform the station of the number of survivors picked up and arrange for medical aid and ambulances if necessary; he can ask for aircraft to help him in his search; and the life-boat can be recalled if the vessel for which she is searching succeeds in reaching shelter.

This last advantage is greatly apprecia- ted by the life-boat crews, especially in bad weather, when they might otherwise continue searching unnecessarily for a long time.

144 life-boats, which include some from the reserve fleet, are also equipped with V.H.F. (very high frequency) radio-telephones for direct communica- tion with helicopters or fixed-wing aircraft of the Royal Air Force or Royal Naval Air Service, which may also be engaged in the rescue operation.

International Distress Frequency While on service, all distress messages are passed on the international distress frequency of 2182 kilocycles (137.5 metres) in the medium frequency band.

This traffic is handled by the nearest G.P.O. or coastguard radio station, and when radio-telephonic silence is imposed because of a distress call, all other traffic is kept off this frequency until the life-boat's service is completed or the distress call cancelled. Because of its comparatively short range, contact with aircraft by V.H.F. is confined to a limited area. The life-boat operator consequently keeps the controlling sta- tion informed of the progress of the rescue operation by his M/F radio- telephone.

The M/F radio-telephones were designed and manufactured especially to meet the Institution's requirements by Coastal Radio Ltd., of Edinburgh, who install and service the equipment on a hire-maintenance basis. The number of such sets fitted is 164. The V.H.F. equipment is supplied by the British Communications Corporation, also on a hire-maintenance basis. It is a modified version of their standard mobile equipment.

Twenty-six life-boats are fitted with D/F (direction finding) loops for use in conjunction with their M/F equipment.

The prime purpose of these direction finders is to enable the life-boat crews to take a bearing on the casualty (provided, of course, that the latter also has R/T equipment) and so make directly for her without having to spend vital time searching an area. Most of these direction finders can take bearings on the radio beacons round the coast and may also, if required, be used for navigational purposes.

Equipment must be Simple All life-boat radio equipment must be, and is. reliable and simple to operate. It has also generally to be stowed in a very small space. There are two types of M/F equipment in use at the present time. They are the type 97, which has been in general use in life- boats for the past ten years and, with the latest modifications, is still giving good service in more than 120 life- boats. The other set consists of the Stentor transmitter combined with the Comet receiver, and is fitted in some 36 life-boats, which require more power- ful equipment. These more powerful sets have all been installed within the past four years. Four life-boats were fitted in 1960 for trial purposes with prototypes of the Curlew equipment, which, if found wholly satisfactory, may eventually replace the older type 97's.

The type 97 was originally specially designed to fit into water-tight lockers on the decks of the smaller boats, although in the larger boats it is installed on a shelf in the cabin. The set in all cases is normally operated by the life-boat's motor mechanic from his seat by the engine room instrument panel in the cockpit, via a remote con- trol unit. The transmitter contains six valves and can operate on any one of four frequencies, selected by a five- position switch. The fifth position feeds the output from the amplifying stages direct to a loud-hailer projector, which can be heard clearly at distances up to five hundred yards. The receiver also uses six valves and is of the normal super-hetererodyne type. A click-stop mechanism on the tuning control en- ables any one of five predetermined frequencies to be located and held.

Shetlands to Surrey The Stentor transmitter has an output of 48 watts, and is thus capable of radiating a very powerful signal. Re- cently a listener in Mitcham, Surrey, wrote reporting that the previous even- ing he had heard the Lerwick, Shetlands., life-boat sending radio messages during a service call. Ten valves are used and it can transmit on any of five crystal- controlled frequencies. These fre- quencies usually are as follows :— 1. The international distress fre- quency, 2182 kc/s.

2. The national calling frequency, 2381 kc/s.

3. The coastguard or Trinity House local service frequency.

4. G.P.O. correspondence frequency (Channel 5 or 6).

5. Any other special local frequency.

The Comet receiver, which is com- plementary to the Stentor transmitter, contains nine valves and is a very sensitive instrument, covering the ship- ping band and the long wave band. It can be used in conjunction with a D/F loop for taking bearings on the radio beacons as well as on a casualty. In addition to the usual knob tuning, any one of three frequencies, one of which is invariably the international distress frequency, can be selected by the turn of a switch. The receiver is then tuned to, and locked on to, the selected frequency by a quartz crystal of the same type as those used in the trans- mitter for controlling the frequency of the outgoing signal. These crystals are so accurately made that they can control the frequency within .002%.

The prototype Curlew equipment uses five valves in the transmitter and is capable of an output of twenty watts into the life-boat's aerial. One valuable feature of this equipment is its efficiency.

It takes less current from the boat's batteries than does the type 97 and at the same time it puts out a signal which is roughly twice as powerful. The receiver uses eight of the recently developed 12-volt valves, which need no external high-tension supply, and has a transistor output stage. A major feature of this receiver is its complete lack of background noise when no signal is being received.

Weekly Tests Every week the life-boat mechanics test their M/F radio telephone with the appropriate coast station. Because of its short range it is not possible to test their V.H.F. equipment in the same way, and each boat is therefore fitted with a small test unit which serves much the same purpose. The output from the transmitter is fed into this test unit and during transmission a lamp lights up, showing that the signal is being trans- mitted; when a voice speaks into the microphone the lamp flickers to show that the modulation stages are in working order. To test the receiver side of this equipment, the test unit contains a fly-power oscillator, which feeds a faint whistle to the receiving stages, and provided these are working efficiently the signal can be heard from the loud- speaker. This signal is intentionally kept at very low power so that in the event of any falling-off of the efficiency of the receiver this signal cannot be heard and a replacement equipment would then be fitted.

Because of the particular conditions in which they have to work, it is un- fortunately necessary for life-boat's aerials to be both lower and shorter than those fitted to other boats of comparable size. The majority of boats now have either single or twin-wire aerials, but some thirteen boats are fitted with twelve-feet whip aerials. The V.H.F.

aerials are only 21 inches long. This length is controlled by the frequency on which the equipment functions.

Echo Sounders Fitted Twenty life-boats are fitted with echo sounders. Five of these are of the recording type and the remainder of the depth indicating type. These instru- ments have been fitted experimentally to allow their value to be assessed under service conditions.

In addition to the output stage of the Curlew receiver, transistors are used in the power supply units of the fluorescent light fittings, which are fitted in the cabins and engine rooms of some of the later life-boats. This class of lighting gives a good shadowless light, which is particularly useful in the engine room.

At night-time it does not destroy night vision to the same extent as does the ordinary filament-type lighting pre- viously used.

Transistors are also used in some of the echo sounders referred to above.

The radio and other electronic equip- ment all take their power from the boat's batteries. All twin-engine boats have two large capacity batteries, which are kept charged by dynamos on the main engines and by an auxiliary generator in boats which lie at moor- ings, or by a rectifier in boats which are housed. In the older boats 12-volt systems were used, but in the newest boats 24-volt systems are standard. The batteries also have to provide power for engine starting, lighting, the search- light, the clear-view screens and an electric kettle..