Transmitter T1154

The T1154 was developed in the late 1930s for the RAF and entered service in June 1940. Over 80,000 were made before manufacture finally ceased in 1950. It is immediately recognised by the brightly coloured control knobs. The transmitter was designed by Marconiís Wireless Telegraph Co at the aeronautical laboratory at Writtle. The design was typical of the innovation at the time and used the then new dull emitter filament technology for the two large power amplifier valves. The transmitter provided telegraphy and telephony with very good speech quality.

It was used together with the companion receiver R1155 in a wide range of aircraft including the Lancaster, Halifax, York, Varsity, Mosquito, Valetta, Shackleton and Wellington.

Transmitter data
The T1154 contains 4 valves and is a variable frequency, master oscillator/power amplifier type of transmitter and is capable of generating a radio frequency (RF) output power of 45 to 70 Watts on CW (morse) and 14 to 17.5 Watts on speech and MCW. It had slightly different frequency coverage to the receiver using three or four switched bands and typically covers 0.2- 0.5 MHz, 3.0 - 5.5 MHz, 5.5 - 10 MHz. The 4-band models split the bands slightly differently and provided coverage up to 16.7 MHz.

Transmit modulation modes are: Amplitude Modulation (AM) for speech plus Continuous Wave (CW) and Modulated Continuous Wave (MCW) for Morse code transmission. The peak modulation is approx. 70 per cent using suppressor grid modulation on both MCW and R/T. The microphone used was either a Carbon granule type or electro-magnetic, using sub-modulator A1134 or A1134A.
The valve line-up is Master Oscillator, sidetone and modulator - two VT105 indirectly-heated triodes; RF Power Amplifier - two VT104 directly-heated pentodes.

The Antenna System was a fixed wire aerial for HF frequency ranges and a long wire trailing aerial for MF frequency ranges.
In airborne installations, both receiver and transmitter were powered by two rotary transformer power supplies which were driven from the aircraft electrical system of 12 Volts or 24 Volts. One transformer unit provided the high tension (HT) and low tension (LT) supply for the R1155 receiver and the LT supply (6V at 4A LT plus 6 volts at 2.5A for the keying relay) for the T1154. The high voltage HT supplies for the transmitter (1200V at 200mA) were provided by a separate rotary transformer unit.
The transmitter measures 17 1/2" wide, 16 3/8" high, 11 1/4" deep and weighs 46 lb 10oz.

The picture shows an T1154 (top) and below it, one with its companion R1155 installed in the Brooklands Vickers Varsity.