Larkspur radio system

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.

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.

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.

The HF set of the family, the C13 was included for use as a short-range combat net radio in circumstances where VHF was unsuitable and could also be used (using AM or CW) for longer range operation by exploiting skywave and near-vertical incidence propagation techniques.

19, it was enhanced during development by the addition of Narrow Band Phase Modulation (NBPhM) facilities to improve the performance and communications reliability at short range particularly at night when ionospheric changes cause increased interference levels.