Part 3, Post War VHF and UHF systems
Post War Air-Sea Rescue
The on long wave and short wave based Gibson Girl transmitters remained in general use for Air-Sea rescue after World War 2, not only by the military but also aboard civil aircraft. Other systems, however, were devised generally based on VHF as were the British 'Walter' and German NS4. This concluding part will not go in detail with every aspect of these later systems, but giving a minor account on some the actual man carried Air-Sea rescue beacons. Two frequencies were eventually allotted to (Air-Sea) rescue operations: VHF 121.5MHz and UHF 243MHz. Some of the radios, notably the AN/URN4, were capable of operating on either frequency. The general tendency was, however, the use of a single band. Most of the radios described in this part operate on 121.5MHz. Not all the Air-Sea rescue transmitters were one-way beacons, some models had limited receive facilities and could be used to make a speech call if a rescue aircraft or ship was within (limited) range. In some systems this facility reduced the working life of the battery. Please note that most of the VHF and UHF air-sea rescue transmitters and beacons (also known as SARBE) were also used to assist in locating of the survivors of land crashes; being small and inconspicuous was a great advantage when forced to be used on enemy territory.
Radio Transmitter/Receiver RT-159A/URC-4 was a VHF/UHF Air-Sea rescue set made in the USA. It was suitable for operation on either VHF 121.5MHz or UHF 243MHz. VHF or UHF operation was performed by a band switch located on the side of the set and the length of the horizontal part of the telescopic antenna. The transmitter might be used for voice or tone transmission and could thus be received by any standard aircraft VHF or UHF receiver. The circuit comprises a three stage crystal controlled transmitter, and a superregenerative receiver with a single RF stage. See the circuit diagram here. The loudspeaker is also used as microphone in transmit position. Use is made of five pencil valves and one 7-pin miniature valve. Shown is the 'yellow' version of this set, also known is a 'green' olive drab version. The battery is connected to the URC-4 by a short connector cable.
British made Search And Rescue And Homing (SARAH) beacon SRI 23006 was a UHF rescue beacon comprising speech unit, transmitter/receiver unit, coding unit and combined LT/HT battery. The first three units are permanently interconnected. Attached to the transmitter/receiver unit is a leaf spring aerial which fold up to very small dimensions. The SARAH beacon has three modes of operation. In the normal beacon condition pulses on a frequency of 243 MHz are being automatically transmitted. See the circuit diagram. The pulses are transmitted in a rate of 210 pairs per second, the spacing between the pulses in each pair is determined by the coding unit and is a distinguishing feature between the beacons. (Note that the normal beacon operation has much in common with the war-time developed 'Walter' beacon). The peak power in this mode is 15 watts and the battery life is about 20 hours continuous operation. Two way speech communication with the rescue craft is possible using the Talk and Listen buttons, the range on speech mode is considerably lower and the power consumption increased. The SARAH beacon was normally powered by a combined LT/HT battery; later versions had a transistorised power supply consisting of a LT battery attached to a transistor inverter.
In Great Britain a variety of different SARBE Search And Rescue Beacons have been developed, notably those manufactured by Burndept Electronics Ltd.
Valves were still used in the SARBE T-10050 (left) transmitter. This set comprises three units: the battery (not shown),
modulator and actual transmitter with (folded) steel tape antenna. Operation is on VHF 121.5MHz.
SARBE TR-9783 (right) was a transmitter-receiver operating on VHF 121.5 MHz. No further technical details are known whether valves or a hybrid of valves and transistors were used.
Noted is the use of a olive drab coloured version, aligned on other VHF air frequencies,
by the Army as an interim for communication from isolated patrol parties to supply aircraft.
SARBE beacon BE 361/243/D was a beacon transmitter operating on UHF 243 MHz. Its size was very small and it was fully transistorised. Believed is that other versions of this pulsed tone beacon operated on a frequency of VHF 121.5 MHz.
Soviet air-sea rescue radio type R 855-U (left) operated on VHF 121.5 MHz and comprised the complete transmitter-receiver and battery unit. The antenna is a vertical telescopic rod of about 60cm in length. The set uses a combination of valves and transistors. Its use is noted in the 1960s. Apart from normal speech transmission and reception, pulsed tone transmission can be emitted. The later issued (about mid-1970s) Soviet type R 855-UM Variation 'C' (right) is functionally very similar in use and much smaller in shape. Operation is also on VHF 121.5 MHz. Transistors are used throughout. A version aligned to 121.7 MHz has been spotted.