Transmitter/Receiver Unit 618T-3

The Transmitter/Receiver Unit 618T-3 is a combined HF Transmitter, Receiver and Power Supply Unit designed and manufactured in the USA by Collins Radio Company. Manufacture started in 1961 and they were still in use until at least 2012. There were military versions used by the RAF, Fleet Air Arm and Army in addition to civilian versions. They were standard fitment to a number of aircraft including the Avro Vulcan, Concorde and VC10. The equipment is also known under its NATO part number TX/RX5821-044. Many thousands were manufactured.

This version of the equipment is different to that produced only 20 years earlier in that the all the various high voltages needed for different stages of the transmitter are all an integral part of the equipment.
Transmitter data
The frequency band covered is 2.0 29.999MHz giving a total of 28,000 channels at 1kHz spacing. The operating frequency is indicated directly in a digital-type presentation on the associated Control Unit. Frequency stability is quoted as 0.8 parts per million per month and the typical channel change time is 8 seconds (up to a maximum of 30 seconds) including the associated matching Antenna Tuner.

The nominal RF (radio frequency) output power is 400W PEP in SSB (single sideband) mode or 100W in compatible AM mode. It is also capable of transmitting in CW (morse) and data modes. The transmitter comprises a total on 13 valves inc a pair of 4CX250s in the PA (Power Amplifier).

It is capable of operating in ambient temperatures between minus 40deg C and plus 55deg C continuously or up to plus 70deg C for maximum of 30 minutes.
Receiver data
The frequency band covered is 2.0 29.999MHz in 1kHz steps.

Sensitivity is 1 V for 10 dB S+N/N ratio on SSB and 3 V on AM.

All spurious responses are at least 80db down and selectivity is typical for an SSB receiver being 2.85 kHz wide 6dB down and 6.0 kHz at 60 dB down.
A Control Unit is available to cover the whole band in 1kHz channels although there is also a version capable of switching in 100Hz channels.

As may be expected, power supply requirements are heavy (!) requiring 28V DC at 35amps and 115V 400Hz single phase AC at 1 amp.

The equipment measures 10 1/8" wide, 7 5/8" high, 22 3/16" deep and weighs 50lb.


Transmitter/Receiver Unit 618T-3