The TRC 77

The TRC 77
By Tony Helm G4BCX

My contribution for this month is Transmitter Receiver TRC 77, the A version (originally US Army). This equipment was originally designed for recce patrols operating in the FEBA (Forward Edge of the Battle Area) using a simple wire aerial slung over a ‘convenient’ tree. This gave a range of 5 to 7 miles (US Army doctrinal range for planning purposes).

The transmitter is a simple affair with 2 valves and 6 transistors in a CO/PA layout, with an 11 transistor superhet receiver. It gave between 10 and 11 watts RF power. A high speed Morse keyer could be coupled to it with a maximum keying speed of 300 wpm and the receiver was quite sensitive and selective. The Tx was CW only, but the Rx could receive AM as well.

The Dutch Army Commandos could see the potential of such a set for their LRRPs (Long Range Reconnaissance Patrols), changed the aerial screw terminal for a BNC connector and made up dipoles, vastly increasing the range - just the job for SPFs (Special Purpose Forces). I do not have any indication of other users at this stage.

	Transmitter	Receiver

No of valves	2 (a 3B4 driving a 2E24)
No of transistors	6	11
Frequency range	3.0 – 8.0 MHz, 6 crystal channels (Rx +455 kHz)
Modes	CW only	AM, MCW, CW
Power requirements	3.75A at 12V	20mA
Power output	10 – 14W	1mW AF
Sensitivity (for 1mW S + noise to noise)		CW: 1m V AM: 2.2m V
IF		455 kHz
BFO		455 + 4 kHz
AGC		AM mode only

Aerials: 3 lengths of long wire, 25, 40 and 57 ft (US Army issue). NB Dutch Army antennas were made from local resources.
Battery: 12V @ 14Ah.

This is a very nice little radio to use, apart from being crystal controlled. The ATU is particularly efficient on Tx, but is bypassed on Rx.
With LRRPs requiring good Rx performance under certain conditions, things would have been better with the ATU on Rx. A plus though, is being able to use duplex, as there are two sets of crystals, one on Tx, one on Rx.

The CW note is good, clean and without chirp. A point to note for purchasers is that the original TRC 77 had a standard jack socket for phones, and a 6 point battery socket on the back. The radio was designed to be carried in the soldier’s Bergen, there being no carrier.

Happy hunting!

Below
Front panel controls, indicators,
switches and jacks.