Army radio communication
during the Great War
Keith Thrower
Circuits developed before 1914
• Diode detector, patented by J A Fleming in October 1904
• Soon superseded by the carborundum crystal detector, patented
by Dunwoody in 1906
• The Audion triode, patented by Lee de Forest in January 1907,
and used initially as a detector. Its amplifying properties were not
realised for several years
• Valve oscillator, patented by Meissner in April 1913
• The heterodyne receiver, conceived by Fessenden in 1901. In its
later form a valve oscillator was used to mix with an incoming
ICW wave and beat it down to an audible tone
• Regenerative feedback from the output of the detector to its
input to improve selectivity and increase amplification
Early radio valves (not to scale)
Fleming diode & BT-H Audion
Round C & T (‘soft’ triodes)
Marconi Short Distance Wireless
Telephone Transmitter & Receiver
• This wireless set used a T.N. valve as
an oscillator, directly coupled to he
aerial circuit
• The C valve is connected as an RF
amplifier with regenerative feedback
to increase its gain and provide
greater selectivity
• The output from the C valve goes to
a carborundum crystal detector in
series with the headphones
The Marconi 1.5 KW spark set
At the start of the war the only radio equipment available to
the army were a 500-watt set and, as shown here, a 1.5kW
set mounted on two wagons each drawn be a team of 4
horses
Spark, CW & ICW Waveforms
• The top waveform shows a typical spark signal repeated every
millisecond
• Below this is a continuous wave (CW) of 200 kHz generated by a
valve oscillator
• The third waveform is that produced when the continuous wave
is switched on and off by a Morse key. This is known as
interrupted continuous wave (ICW)
• Spark transmitters were used throughout WW1 but ICW radios
began to come into service from late 1916
No 1 Aircraft Spark transmitter
• The Royal Flying Corps (RFC) was first to use tactical radios
• 600 of these transmitters came into service during 1915
• Transmitter box measured 8in x8in x5in. However, a heavy
6-volt accumulator was required to power it
Damped oscillations from spark generator
• It should be noted that the oscillations will be further
apart than shown here
• Typically there will be between 100 and 1000 damped
oscillations per second
W/T Trench Set 50 Watt D.C. (BF Set)
• Transmitter derived from the
No 1 Aircraft Spark
• Simple receiver with
carborundum crystal
• Came into service in 1915
• Transmitter operated on
350, 450 & 550 metres
• Powered from 10V battery
• Total weight: 112lb
• Range 4000yd (2.3 miles)
• 1200 produced
W/T Trench Set 130 Watt Wilson Transmitter
• Division to Corps
communication & Corp
Directing Station
• Fixed spark gap with motordriven high-speed interrupter
• Same wavelengths as BF Set:
350, 450 & 550 metres
• Range 9000yd (5.1 miles) with
aerial supported on 30ft
masts
• Powered by 26V or 28V
accumulator
Crystal detectors
• Two types of crystal detectors were used in the receivers:
1. Carborundum, composed of silica and carbon, invented
by Dunwoody in 1906
2. The Perikon, a combination of zincite & chalcopyrites,
invented by Pickard in 1909
• Carborundum was more robust but required a bias of 1½ to 3½
volts, adjusted by a potentiometer
• Perikon was more sensitive and did not require a bias battery, but
was also more delicate in use and easily knocked out of
adjustment
• Several army radios had both types fitted, with selection by a
changeover switch
• A test buzzer was usually included in the radios
Tuner Short Wave Mk. III*
• Mk. III version introduced in
1916. Mk III* in 1918
• Covered band 100–700m
• Used with Wilson 130-watt
transmitter & for aircraft
flying over trenches
• Carborundum & Perikon
crystals in receiver
• Aerial 125ft wire laid along
the ground as inverted L
Later valve developments (not to scale)
Left) French TM of 1915
Manufactured in UK as
R-valve in 1916
(Right) Type F transmitting
valve. Derived from R-valve
(Top) Marconi Q detector
valve: 1916
(Bottom) Marconi V24
amplifying valve: 1918?
W/T Forward Spark 20 watt “B”.
The Loop Set
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Used for forward communication
There we both Rear & Front Stations & two versions of each
They had a fixed wavelengths of 65m & 80m (5MHz & 3.75MHz)
Transmitter had a fixed spark gap similar to the BF Trench Set
Receiver had two valves, either the French TM or British R
W/T Set Trench CW Mk III*
• The transmitter & receiver were mounted in separate boxes
• Entered service in 1917
• Transmission was by interrupted continuous waves (ICW), which
required a heterodyne receiver
• Apart from the transmitter and receiver the complete station
included a Selector Unit, a heterodyne wavemeter, an AC power
unit and an associated rectifier unit
W/T Set Trench CW Mk III*: Transmitter
• Used for Forward area comms
• Transmitter rated at 30 watts
• Band covered: 450–1450m
(207 kHz–667 kHz)
• Earlier Mk III version had
single B or AT25 valve. This
version had two valves
• Aerial 20 to 150ft depending
on wavelength, supported by
masts. Also 14ft earth mat
• Range 3.7 miles
• Approx. 3000 manufactured
W/T Set Trench CW Mk III: Receiver
• This is the Mk. III receiver and
has two R valves
• One is used as an oscillator to
mix with the incoming ICW
signal and beat it down to an
audible frequency
• The other an AF amplifier
connected to the headphones
• Approx. 3000 manufactured
• There were also approx. 400
Selector Units manufactured
Telephone Wireless Aircraft Mk. II
• Special helmet produced with
in-built microphone &
headphones
• Wireless telephony from
aircraft started in mid-1917
• This set covered the band
350–450m (667 kHz–857 kHz)
• It had two B or AT25 valves
• Powered rom a 6-volt battery
& a wind-driven 600-volt
generator
• Aerial a trailing wire 100-150ft
Concluding remarks
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Army was slow to adopt wireless and relied too much on cable
Genuine fear that wireless would be intercepted by enemy
But this was equally true with communication by cable
Cable was being constantly severed by shell fire and passage of tanks
The first tactical radios to be used were those fitted in aircraft from
1915 to communicate with crystal receivers on the ground
First trench sets came into service in the towards the end of 1915
After this the army slowly began to realize that wireless was a more
reliable way to communicate than cable
Only in last year of the war was wireless sets readily adopted by the
army
One wonders how much shorter the war may have been and lives
saved if wireless had been adopted in large numbers from 1916
onwards when improved valves became available, making possible
communication by continuous waves
Modulation of oscillator to produce ICW