GRC-106

This sixties vintage tranceiver is my favourite rig. Built in th US by General Dynamics, it was used in Australia by the RAAF and the Army. It operates on CW and USB, full coverage from 2 to 30MHz. It's synthesizer has a crystal oven for ultra high stability. It emits 400W PEP on USB and 200W on CW. It is beautifully constructed, with no expense spared. It's an ideal rig for ham work. The only downside is that it pulls 37A at 28V DC. The GRC-106 consists of a RT-662 reciever exciter (center of above photo) and a AM-3349 linear amp (top). The MD-522 is used for FSK/RTTY teleprinter operation.

COMMENTARY

The GRC-106 is intended primarily designed as a ground or vehicular radio. It has mounting brackets for vehicular use and can tune a vehicular mounted 15ft whip. It is quite compact and operates off 28Volts.It uses common GRC type audio accessories.

Quite a lot of thought has been put into the usability of the set, with a minimum of controls. It was obviously designed to be used by army grunts. 

The RT-662 exciter is a pleasure to use. The operator just selects the desired frequency using rotary switches on the front panel. A turret containing the tuning coils is rotated by a servo motor to select the correct set of coils. A vernier allows receiver fine tuning. The only other controls are the mode switch, rf gain, audio gain, squelch, VOX mode and BFO control.

There are connections for IF in and Out, and 5MHz frequency standard out. The antenna connection is normally routed through the linear amplifier. There are two parallel audio connections. Other connections are power in and control cable for the linear amplifier. A meter displays received signal strength

The AM3349 linear amplifier is also designed to be as simple to operate as possible, without sacrificing performance. Two antenna connections exist, a UHF type connector and a connector for the 15ft whip.
A meter switch allows crucial voltages to be monitored. 

The metering arrangement is extremely simple, instead of a standard legend, there is a green colour band.
If the reading is in the green then it's OK. There are two meters used for tuning, Tune and Load. When correctly tuned they will both be in the centre of the scale. To tune the set the operator selects tune, which keys the transmitter. He then rotates the Tune and Load knobs alternately in the direction he wishes the corresponding meter to move.

There is also a turret in the linear, which is rotated to the correct MHz frequency range controlled by signals received from the RT-662.

The MD-522 unit is more than just a modem unit. It allows a slave RT-662 receiver exciter to be integrated into the system. This allows full duplex voice or RTTY operation, or simultaneous voice and TTY operation.

The set is pretty good for ham work. It covers all the HF bands except for 160Metres, although it is USB only, but this still leaves plenty of ham bands that are USB. It needs 28Volts @ 37Amps, but any military radio fan will need to have a power supply capable of this anyway. The antenna tuning unit is a dream. I have a 40 metre dipole which I forcibly tune. This thing was designed to load up a wet piece of string.

TECHNICAL SPECIFICATIONS

RT-662/GRC

Frequency Range      2-29.999Mhz in 1KHz steps, vernier control on receive
Modes                      USB, AM compatible USB, CW, FSK
Frequency Control    Crystal controlled synthesizer referenced to 5MHz frequency standard
Primary Voltage        27Volts
Exciter Power Output    0,1W PEP
Receiver                    Triple Conversion Superheterodyne with dual valve front end
Receive Bandwidth        3.2kHz via crystal filter

AM-3349

Power Requirements    37Amps at 28Volts
Power Output
    SSB    400W PEP
    CW    200W RMS
    FSK    200W RMS    
    Tune    50W RMS        (power outputs individually adjustable via pots)
Antenna    15ft Whip or Doublet
 

MD-522A/GRC

Modes of operation:
    fsk, nsk, voice, 85 Hz diversity, 85Hz plus voice
Data Rate    75bps
Internal Loop Voltage    up to 120 Volts
Signal Levels    space 0mA, mark 20 or 60mA

CONSTRUCTION

Below: RT-662/GRC Receiver Exciter

Below: RT-662/GRC top view. The cover for the turret has been removed. The modular construction of the set is apparent from this shot.

Below: The turret from the RT-662/GRC. The two valves for the front end can be seen in the centre of the turret. Each small biscuit circuit board corresponds to a Megahertz band.

Below: RT-662/GRC bottom view. The servo arrangement to drive the turret can be readily seen.

Below: An example of the construction standard of the set. This module is part of the IF stage.

Below: AM-3349 linear amplifier

Below: AM-3349 top view. As can be seen the linear also has a turret. It is set to the correct position based on signals from the RT-662/GRC.

Below: AM-3349 with shielding removed. At left of photo is the antenna tuning unit. Note the massive vacuum variable capacitor. At centre are the photo are the two 4CX350F valves which are the finals.

MD-522A modem unit

MD-522A top view

MD-522A bottom view

OVERALL RATINGS

    Engineering rating (taking into time of design).

             A work of art. 10/10

    Fitness for purpose rating

             More than thirty years old and this equipment is still in active service because modern equipment is
             not up to scratch. 10/10.

    Usefulness as ham equipment rating

             Very nice receiver although a little difficult to scan with. Transmitter is USB only. 
            Very functional antenna tuning unit. 8/10

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