FR-12  Transmitter-Receiver

During WWII, the FR-12 was a mainstay on many RCN vessels and was used on CW for inter-communication between escort ships on convoy runs. Voice was available but rarely used.  The popularity of the FR-12 dropped when the TBS transmitter/receiver was introduced into service.  On low wave band, the set had a range of about 20 miles.

In a peacetime navy,  the FR-12 was used to communicate with merchant ships or the Naval Administrative Net (at sea). Pictures taken in the 1950's show the handset installed, so it was definitely used on voice. Emergency communications could be provided by the FR-12 since it only operated from a 12 volt DC power source. The receiver section consisted of a five tube superheterodyne design with the ability to continuously tune the range of 375 to 4200 KHz in three bands. To simplify the overall design, there was no direct frequency readout for the receiver. Instead, a circular logging scale dial was provided. It was necessary to calibrate the dial, and record the readings in advance.

The transmitter section had an oscillator, a modulator and a dual power output stage. One of four, selectable, internally mounted crystals determined the operating frequency. In order to activate the modulator, one simply inserted the handset plug into the front panel socket. The microphone in the handset provided the interlock for the modulator. If this was done while the Dynamotor was running, a noticeable slow down of the Dynamotor could be heard.

Power for the FR-12 could be provided by one of two modes. In standby mode, the filament circuit for the transmitting tubes gets disabled. Filament power for the receiver would be provided from the main battery. The 180 volt B+ line for the receiver would be furnished from four, external, 45 volt dry batteries wired in series. Standby mode would dramatically increase the life of the main battery. In normal mode, all power for the receiver and transmitter was provided by the main battery. An internal Dynamotor produced high tension for the transmitter but it had to be inspected after every 500 hours of operation. Input power to the FR-12 was 12 volts DC at 6 amps on receive and 13 amps on transmit when used in normal mode.

Al Goodwin of Dartmouth N.S. did some range experiments with the FR-12. "It was sent away in a sea boat on a couple of occasions. In those days, we didn't have commercial mobile antennas available to us, so we rigged up a 35 foot whip antenna. The exercise was not deemed a success as we lost communications around five miles. On HMCS HAIDA, we used this set for both AM and CW communications. For CW operation, we would have to attach a key with a very long lead. In an unusual case, the late Keith Lake (VE1PX) used the FR-12 to modulate the Marconi PV500 transmitter thus giving it AM capability for use on the amateur bands. He put out quite a strong signal compared to the 30 watts of the Marconi CM11".

Normally the FR-12 would have a feedthrough insulator in the upper left hand corner. In peacetime, the RCN modified these sets so the antenna was interconnected with coaxial instead of antenna trunking.  (Photo by Jerry Proc)

Types: FR-12 (12 volt) #85161-T
             FR-12 (32 volt) #85135-T

Modes: CW, MCW and Voice
Frequency Coverage: LF transmit  - 375 to 580 KHz
                                      HF transmit - 1580 to 4200 KHz
                                      MF Receive only  - 550 to 1600 KHz
MCW oscillator  1,000 Hz
Power Input: 15 watts on CW, less on MCW and even less on voice.
Frequency Control: Four crystal controlled frequencies.
Receiver IF: 260 KHz
Weight: 69 lbs.
Duty cycle: 5 minutes transmit followed by 5 minutes receive, otherwise the Dynamotor will overheat.
CIrca: February 1942 as dated in the manual.
RCN Ref. Number: 5820-21-041-1615

Above and below: This pristine and unmodified example of the FR-12 is owned by Meir Ben-Dror  WF2U. Note the RF feedthrough insulator to the left of the meter. (Photos by Meir Ben-Dror)

FR-12 - top view of chassis. (Image courtesy Canadian Marconi)
Another example  of the FR-12 chassis top view. (Photo by Jerry Proc)
FR-12 - bottom view of chassis.  (Photo by Jerry Proc)
There were lots of variants for the Unit Type Number of the FR-12 . These express the ratio of LF versus high frequency channels which were ordered from Marconi. As an example the following mix of channels could be ordered from Marconi:

85135S   (32V)  Channels 1 and 2 for LF; Channels 3 and 4 for HF
85161S   (12V)  Channels 1 and 2 for LF; Channels 3 and 4 for HF

85135AS (32V)  Channels 1, 2, and 3 for LF; Channel 4 for HF
85161AS (12V)  Channels 1, 2, and 3 for LF; Channel 4 for HF

85135BS (32V)  Channel 1 for LF; Channels 2, 3, and 4 for HF.
85161BS (12V)  Channel 1 for LF; Channels 2, 3, and 4 for HF.

A  -H in the model number indicates that the remote control option was installed. The manual does not do a good job in explaining the variants. In the back of the manual there is a hand written note indicating PH , TH and BRA variants. No further explanation was provided.


FR-12 (12 volt) #85161
FR-12 (32 volt) #85135

FR-12's were still being reconditioned as late as October 1963 as evidenced by the tag on FR-12   S/N 128 owned by Meir Ben-Dror.

Note the position of the feedthrough and the item in the top right corner. 
In the variant above, the RF feed-through connector is positioned to the right side of the leftmost meter instead of to its left. Something has been added to the top right corner  in area which is normally blank. The crystal access hole cover is also fitted wit a knob of the same type as found on the front panel. This FR12 was fitted in the vessel RCMP Irvine in 1950. Was this the very first version of the FR12?
This FR12 was fitted in the radio room of HMCS Rupert in 1942. The RF  feedthrough insulator is fitted at the top of enclosure with the wing nut barely visible. Bare copper transmission line can also been seen in the upper right hand corner of the photo. (Public Archives Canada Photo HS-0262-1 submitted by Spud Roscoe)

FR-12 in Fairmile Q112. (Photo via James Taylor)
This FR-12 was fitted in Fairmile Q112 while still at the builder's yard. Note the absence of the RF feed-through insulator at the top left corner of the front panel. Instead it appears to be placed on top of the unit. At the lower right side of the speaker is the clip for the fold-up Morse key which is not shown here.
Model CD-12

Except for differences in frequency coverage, the CD-12 was the version of the FR-12 built for the Canadian Army. Both the CD-12 and the FR-12 came with a swing-down key attached to the front panel.  In addition, the CD-12 had an accessories lid. See the CD12 document for more details.


The following documentation is available for download:
FR-12 Manual
FR-12 Schematic . This is a 36 inch x 24 inch schematic which has been scanned at full size and saved in both JPG and PDF formats. To print the schematic, simply download it then bring the file to your local graphics shop for printing. 
FR12 schematic in JPG format
FR12 schematic in PDF format.
CD-12 Overview Sheet


The nameplate on the dynamotor made by Robbins & Myers indicates an output voltage of 350 VDC at 225 ma.

Contributors and Credits:

1) Meir Ben-Dror, WF2U <wf2u(at)>
2) Marc-André Morin <marc-andre.morin(at)>
3) Tom Brent <navyradiocom(at)>

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Dec 15/16