Larkspur radio system

Larkspur was the retrospectively adopted name of a tactical radio system used by the British Army. Its development started in the late 1940s with the first equipments being issued in the mid-1950s. It remained in service until replaced by Clansman in the late-1970s although some elements of Larkspur were still in service well into the 1980s. It was widely exported to British Commonwealth armies and other friendly nations.

The origin of Larkspur was a post-war project to move tactical short-range radio communications in the forward battle area from HF using amplitude modulation to low-band VHF using frequency modulation. This followed the similar move by the US Army in the latter part of WWII which had demonstrated significant advantages. Where the use of VHF was not practical, HF sets using narrow band phase modulation (NBPhM) were developed as the only practical method at the time of obtaining some performance improvement over the use of AM especially at night.

The range of sets originally comprised the vehicle VHF sets C42, C45, B45, B47, B48 and the C13 vehicle HF transceiver, all of which were designed to specifications produced by the government Signals Research and Development Establishment (SRDE) at Christchurch and initially designated as the "New Range" to differentiate them from wartime legacy radios. They were characterized by similar appearance, tuning drills, frequency indication using film strip displays, the use of relatively simple architecture that avoided complex switching as far as possible and using commonly available components and a degree of modularity in construction. Plessey Mk.IV connectors were used extensively in the sets and accessories.

An important operational advance was that the sets incorporated internal calibration facilities which meant that they could be accurately pre-set on a frequency without radiating any signal. This enabled all stations in a net to be confidently pre-tuned on the same channel and eliminated the old compromising "Tuning and Netting Call" system that advertised the presence of activity to an enemy.

All the sets were constructed in strong hermetically sealed alloy enclosures - a measure that had been found to be essential to ensure durability and reliability during the previous war, and were sized to fit a standardized range of vehicle mountings. A range of control and distribution accessories known as a harness to enable radio facilities to be accessed from various points in a vehicle was also produced.

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