CGRT-1 Transmitter


Type: High  powered  transmitter; RCN stock # 5820 000060
RCN Manual reference: BRCN 2623
Frequency range: 4 to 27 MHz
Modes: CW, MCW and Phone
Power out : 20 kw
Mains power: 575 VAC, 3 phase 60 Hz
Circa:  July 1955
Made by Canadian Marconi
Comment, The front of the manual indicates two  Marconi contract numbers, both bearing serial numbers. The only possible RCN  use by a transmitter of this power level would be at the RCN's transmitting sites at Newport Corners N.S. and Matsqui B.C.


1. The RCN CGRT-l Transmitting Equipment as manufactured by the Canadian Marconi Company, is designed for use as the main high frequency transmitter of a naval shore station and to be used for communication with ships at sea and with other distant shore radio stations. The equipment has a nominal power output rating of 20 KW, and operates over the frequency range 4 to 27 MHz on Radio Telephone, Radio Telegraph, and Radio Teletype Frequency Shift emissions.

Number; of Channels and Types of Emission

2. The equipment comprises two complete radio frequency channels served by a common power supply and, if installed, a common modulator. Thus full power output is available from both channels simultaneously, or with both channels on either radio telegraph or frequency shift operation; with one channel on radio telegraph and one channel on frequency shift operation, or with one channel on radio telephone and one channel on either radio telegraph or frequency shift operation. In some cases the modulator is not installed, so that radio telephone operation is not possible.

Local and Remote Control Systems

3. Operation of the transmitter can be controlled either locally at the transmitter, or from either, or both, of the two remote control positions. The master control position is located at the transmitter site, and at this position it is arbitrarily determined whether the control shall be local or remote. Control of the following facilities is available from each of the three control positions:

(a) On-Off Switching
(b) Standby-Operate
(c) Channel Selection
(d) Emission (ie. - Radio Telegraphy, Radio Teletype Frequency
shift, or Radio Telephone if a modulator has been installed).

At the remote control positions the channel and the type of emission to be used by each operator at any time is a matter for agreement between those operators.
Indicating devices are provided to prevent the use of conflicting facilities by the  remote operators at the same time. All control operations are initiated by the
local and the remote operators through the use of individual telephone-type selecting dials.

Power Supply

4. The transmitter is designed to operate from a power supply source of 575 VAC , 3-phase, 60 Hz. The power demand is approximately 125 KVA at 95% power factor, with full power output from both channels simultaneously, and with one channel modulated 100%. The local and remote control units operate from a 115 V, 60 Hz power source and draw approximately 1. 5 amps  each. A separate 115 VAC  60 Hz power supply capable of delivering 200 VA, is required for the heaters of the crystal ovens.

Output Impedance

5. Both channels are designed to work into a transmission line with nominal impedance of 600 ohms balanced to ground, with a standing wave ratio
of not more than 1. 250

Frequency Control

6. Frequency control is by means of crystal or master oscillator, with provision for 10 crystals per channel in the crystal oscillator. Quartz crystals type CR18/U, or an external frequency shift keyer, of output power 1 watt mini mum in 72 ohms, may be used. The output-to-input frequency ratio is 2 from 4 MHz to 8 MHz:, 4 from 8 MHz  to 16 MHz;  8 from 16 MHz to 27 MHz.

Design Features

7. The equipment has been designed so that a complete frequency change on either channel, from any frequency in the overall operating range of any other frequency in the overall range, can be made by one operator in 5 minutes or less provided these frequencies have been logged in advance,

Air cooling is used for all components, including vacuum tubes and iron cored components. On radiotelephone operation, circuits for the prevention of overmodulation by peak-clipping, and for the elimination of background noise by squelch action between words and sentences, can be introduced by the operation of a switch.  On telegraph operation, electronic keying is used, and keying speeds up to 400 words per minute can be obtained. The front panel of each main unit of the equipment carries a door interlock consisting of an electro-mechanical device which is arranged so that it removes high operating voltages from all exposed components, and grounds those components before access can be gained to them. In addition, grounding rods are provided at convenient points in each unit.

8.  A typical installation, consists of a HV rectifier, LV rectifier, modulator, two PA units and a driver with associated transformers, ductwork,
blower and voltage regulator, These components require a floor space of 13 x 30 ft with a ceiling height of 11 to 12 feet , Such an arrangement permits the transmitter to
be mounted on a 20 inch platform with manifolds underneath and with transformers, blower, etc,., at the rear of the transmitter.

9. The weight of the entire system is 16,200 pounds.

There are 71 rubes in this transmitter if fitted with a modulator.
The major components of the transmitter are:

Power Amplifier Unit for Channel 1  #117-932
Power Amplifier Unit for Channel 2  #117-932
Driver Unit                     #117-933
Modulator Unit              #117-931
High Voltage Rectifier #117-936
Low Voltage Rectifier  # 117-934

The manual used as the source  has a lot of missing pages so its not possible to show a complete transmitter  As a result, only selected views will be shown in the table below .

Block diagram - left half 
Block diagram - right half
Drive Unit 
Local Control Unit
Low Voltage Cabinet 
Power Amplifier
Remote Control Unit 
Weights and Dimensions

9C25 power triode. There were two of these in the modulator and two in  the high power  RF Amp stage.  To light up each of them up, a 6 volt , 285 amp power source was required .  Each 9C25 weighs 120 pounds. Dimensions are 14.25" Diameter by 17.375" High. Full 9C25 specs. (Photo courtesy  Canadian Marconi) 
Due to the weight of each tube, an internal tube hoist was provided to facilitate the replacement of a soft or defective tube,  (Photoscourtesy  Canadian Marconi) 

Contributors and Credits:

1) Jim Fleming
2) 9C25 tube specs courtesy

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Apr 8/20