Michael Marinaro WN1M makes a welcome return, with an overview of the major radio systems used in WWII aircraft and, later, often found on the surplus market and pressed into amateur radio service.

 

World War II brought an unprecedented need for military radio in the air, at sea and on the ground everywhere but particularly so in the European air war theatre. The Royal Air Force (RAF), the Royal Canadian Air Force (RCAF) and the American Army Air Forces required reliable and efficient ground-to-air and air-to-air communications for their fighters and bombers. The demand was enormous and crucial to the accomplishment of the missions of the Allied air forces – the achievement of air supremacy. The stakes were high and the responsibly staggering.

Technology met these exceptional challenges with innovative and versatile equipment designs. The equipment that emerged operated CW, Modulated CW, AM phone and, in central systems, teletype. It covered short or long ranges and, importantly, was intended for use by more than one Service. The electronics designers and the radiomen and wireless operators became significant contributors to the ultimate success of the Allies.

 

Typical American System

I present here a characteristic ‘American’ system of the era, which met the rigorous needs of the US Army Air Force and was also used by the Allies on specific missions. This system was used in the B-17 (Flying Fortress, Fig. 1), B-24 (Liberator) and B-29 (Superfortress) bombers.

Generically known as Command Sets, AN/ARC-5 was the overall designation applied to the system of units used by the US Navy in their aircraft for LF, MF and HF communications and navigation. The Army Air Force and Signal Corps adopted SCR-274-N for their parallel system of components.

Although similar in many respects, the Navy and Air Force systems were not interchangeable. Individual components within each system were identified with unique model numbers pertaining to their function, service and application. Table 1 details the various units and their designations.

The systems were customised and assembled into modules for specific service in various aircraft utilising:

Rack mounts

Adapters

Control boxes

Dynamotors

Relays

Antenna switches

 

Command Sets

The components comprising a SCR-274-N system installation aboard an aircraft varied by the requirements of the theatre commanders. Major considerations included inter-squadron and air-to-ground communications, form of navigation; and frequencies and modes employed. Satisfying these variables resulted in a number of different combinations of basic components. Generally, the result would be a rack of three receivers along with a rack of two transmitters and accessory components for interconnection, Fig. 2. The core units could be augmented with additional racks and other specialised units. The circuit diagram, Fig. 3, is of a typical Command set transmitter.

 

RAF Radio System

In parallel, RAF Bomber Command adopted standardised radio systems for their bombers. The photos, Figs. 4 and 5, show the arrangement available to the Avro Lancaster and other multi-engine craft, while Table 2 lists the equipment types. The R1155 and T1154 will be very familiar to many PW readers.

The components were assembled into packages for integration into various aircraft using power supplies, mounts, antenna switches and so on. Standardisation was an important objective in order to simplify the role of the radio/wireless operator who often also served as a gunner.

 

Fighter Installations

Consistency was also sought for the pilots who flew the Defiant, Hurricane, Spitfire and other fighters. These aircraft used the RAF series TR-1143, a VHF single-case system, based on the American SCR-522-A system. The radio systems and the installations were identical, avoiding the necessity of retraining every time the pilot flew a different aircraft type.

The relative merits and deficiencies of the various systems are debatable but all contributed significantly to Allied success. The designers as well as the wireless/radio operators distinguished themselves and earned a special niche in the annals of the conflict.

The units were manufactured by the hundreds of thousands and, post-war, presented a bonanza to radio amateurs in Britain, the US and elsewhere. Inexpensive, new and used units were creatively converted for every band and most modes of operation. Intensively in the 1950s and 60s, and reducing later, the units renewed their mission. If you listen carefully to the activity on the CW portion of the bands today, you may hear a proudly restored unit still celebrating its resurrection.

 

PW

 

Table 1: Typical SCR-274-N System Aircraft Installation

 

Model               Description                Frequency (MHz)

BC-946            Receiver                      0.52-1.5    

BC-454            Receiver                      1.5-3.0

BC-454            Receiver                      3.0-6.0

BC-455            Receiver                      6.0-9.1

BC-696A          Transmitter                  3.0-4.0

BC-459A          Transmitter                  7.0-9.1

BC-456            Modulator

 

Table 2: Aircraft MF/HF System-MCW, CW & R/T as used in Avro Lancaster

 

Model                           Description      Frequency (MHz)                    Power

R-1155                          Receiver           Five Ranges (0.20 to 18.5)

T1154 (A through D)     Transmitter        Ten Ranges 0.20 to 30.0          40 to 70W

 

This article was featured in the September 2018 issue of Practical Wireless