CM11 Transmitter-Receiver
First built in 1942,
the CM11 was a transmitter/receiver that was capable of operation in the
375 KHz to 13.5 MHz range. There were two distinct bands of operation:
375 to 515 KHz on low frequency and 1.5 to 13.5 MHz on high frequency.
In the high frequency band, the CM11 could be used with crystal or master
oscillator frequency control. For low band operation, only the master oscillator
could be used. The RCN labelled CM11 crystals with two additional frequencies
besides the fundamental - the second harmonic and the third harmonic. On
HF, the transmitter could be tuned to operate on any of the three frequencies.
Modes and power levels were: CW - 100 watts; MCW - 70 watts; AM - 30 watts.
The Signal Electric R63 was the key provided with the CM11 - RCN
pattern number 3M/103.
The transmitter chassis
is called a TM-11 and the receiver is the familiar CSR-5 . When packaged
together as a system, the receiver, transmitter and antenna tuner become
the CM-11. If the transmitter and the antenna tuner were sold without the
CSR-5 receiver, it would be called a TM-11.
CM11's in service
with the RCN were modified to operate with a "Man Aloft" key. This safety
feature prevents the final RF stage in the transmitter from being energized
in case f someone has to climb the mast to work on the antenna. Generally,
the lock was fitted to the cabinet of the CM-11 at the left side near the
top. In the example below, it was fitted on the CSR-5 receiver of the leftmost
CM11.
Inter-connection
between the transmitter, receiver and antenna tuner was provided by snatch
plugs and electrical bus. These connectors operate on the same principle
as knife switches. Each of the three slide out assemblies in the CM11 are
equipped with female snatch plugs. When slid into place, the antenna tuner,
transmitter and receiver interconnect through a wiring bus that is fitted
with male snatch plugs. The CM11 antenna tuner was a very versatile
device, since it could match antennas that were 5 to 750 ohms resistive
and supported operation in the range of 375 KHz to 13.8 MHz.
Keith Kennedy ex-C2NET(s)
of Surrey BC notes that "the CM11 was notorious for generating harmonics
and spurious emissions and HMC Ships would routinely receive harmful interference
reports from the Department of Transport monitoring station located at
Wetawaskin Alberta. We had little in the way of test equipment and certainly
nothing as fancy as a spectrum analyzer so we just followed the CM11 tuning
instructions and filed the reports away. The CM11 was also known for its
chirpy CW signal when controlled by the master oscillator but it behaved
properly under crystal control. CM11's also had a bad habit becoming detuned
as the ship rolled. It was the result of changing capacitance between the
antenna and the surface of the sea".
Eventually, the CM11
was superseded by the AN/URC32 transceiver in the Royal Canadian Navy.
Frequency
Range: LF - 375 to 515 KHz
HF - 1.5 to 13.5 MHz
Modes: CW/MCW/AM
. On MCW the note is fixed at 1,000 Hz.
Frequency Control:
Crystal or Master oscillator.
RF Power: 100 watts
on CW; 70 watts on MCW and 30 watts on voice.
Antenna Impedance:
Will match antennas that are 5 to 15 ohms resistive on LF or
15 to 750 ohms resistive
on HF.
Primary Power: 115
VAC @ 5.4 amps, 60 Hz or 24 VDC @45 amps.
Weight: 478 pounds
including power supply.
Colours: The CM11
is known to have been painted in:
a) a tan , mat finish
b) light, smooth
gray enamel.
c) Medium dark,
blue-gray crackle finish.
d) light green
The ZM-11
power supply consists of three separate assemblies. From left to right:
1) Transmitter low
voltage power supply. #102-902
2) Transmitter high
voltage power supply. #102-900
3) Receiver power
supply. #102-903
The ZM-11 power supply
can operate on 120 VAC or 24 VDC power sources. A 20 second time delay
circuit prevents power from being applied to the transmitter in order to
protect the mercury vapour rectifiers. There was an emergency mode which
decreased the time delay to 4 seconds but at the expense of shorter mercury
rectifier life.
CM11-A
This documentation
has scanned from BRCN 2769 which is the RCN version of the Canadian Marconi
CM11 manual. Because some of the Figure drawings in Section 8 are larger
that the bed of a normal scanner, they have been scanned separately and
some have been split into left and right sections in the interest of printing
convenience. After printing, these documents can be taped together
and trimmed to reconstitute the original information.
