The Wireless Set No. 12, also known as the Sender No. 12, was a British Army HF valve transmitter developed around 1940–1941 and used extensively during the Second World War. It was designed for reliable communications between military formations, particularly at divisional level, and could be operated from a vehicle or a fixed ground station.
Unlike many military wireless sets, the No. 12 was a transmitter only. It was normally paired with a separate receiver, most commonly the British Reception Set R107.
Specification
| Feature | Details |
|---|---|
| Frequency coverage | 1.2–17.5 MHz |
| Output power CW | Approximately 25 watts |
| Output power AM | Approximately 7 watts |
| Operating modes | CW, MCW and AM telephone |
| Frequency control | Variable or crystal controlled |
Its main stages
- Oscillator: Generated the operating frequency, using either a variable-frequency oscillator or crystal control.
- Buffer and multiplier: Isolated the oscillator from the power amplifier, helping to maintain frequency stability.
- RF power amplifier: Increased the signal to the required transmitting power.
- Audio modulator: Allowed microphone speech to modulate the carrier for radio telephone operation.
- MCW oscillator: Produced a 900 Hz tone for modulated Morse transmissions.
A particularly useful feature was its improved oscillator stability. The additional buffer stage reduced frequency pulling when the output stage was tuned, making the transmitter more stable than many earlier designs.
The Wireless Set No. 12 High Power
In 1942, a more powerful development appeared, known as the Wireless Set No. 12 HP. This employed the standard No. 12 as an exciter, feeding a separate high-power RF amplifier.
The HP installation could produce approximately 250 watts on speech transmissions, greatly increasing its usefulness for long-distance military communications. It was used in command and headquarters vehicles, including specially equipped three-ton wireless lorries.