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Army radio communication during the Great War

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1 Army radio communication during the Great War
Keith Thrower In this talk I am going to describe some of the radios used by the British army on the Western Front during the Great War. There are more details in the written paper I will show that there was a great reluctance by the army to adopt wireless, particularly during the first two years of the war. Instead, the army relied too much on use of cable for sending messages and the cables were constantly being broken by shell fire and the passage of tanks, so that reliable communication was always difficult and, often, impossible. If wireless had been adopted more speedily during the war it could have made a great difference to its outcome and probably saved many thousand of lives I will start my talk by outlining the state of wireless progress prior to the outbreak of war in August 1914.

2 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Diode detector, patented by J A Fleming in October 1904 Soon superseded by the carborundum crystal detector, patented by Dunwoody in 1906 The Audion triode, patented by Lee de Forest in January 1907, and used initially as a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 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 On this slide I have listed the most important circuits that had been developed before Most of these were not used in army wireless sets until 1916 The first valve to be used as a detector of telegraphy signals was the diode which was patented by John Ambrose Fleming in October 1904 By adding a control element to the Flemings diode Lee de Forest produced the Audion, an improved detector which he patented in January This valve had hidden amplifying properties that were not realised for another five years. The valve later became known as a triode The German, Alexander Meissner, produced the valve oscillator by feeding back some of the output from the triode to its input. He patented this invention in April 1913 The heterodyne was one of the most important circuits to be developed. Its origin goes back to a patent by Fessenden in In its later form a valve oscillator in the receiver was made to mix with an incoming telegraphy signals and to beat it down to an audible tone Another important circuit was regenerative feedback from the output of a detector to its input, not sufficient to cause oscillation, but it improved the selectivity and significantly increased the amplification.

3 Early radio valves (not to scale)
Fleming diode & BT-H Audion Round C & T (‘soft’ triodes) Shown here are: A commercial version of the Fleming diode which was used in some of the early Marconi radios but soon superseded by a crystal detector An Audion triode of BT-H manufacture. This was used in the Mk. III amplifier but the valve was not reliable and had poor performance At the right are two ‘soft’ valves designed by Henry Round of the Marconi Company in 1913 and manufactured by the Edison Swan Company The smaller of these is the type C which was a receiver valve used as an RF amplifier or detector The other is the type T transmitter valve. This was fitted with two or three filaments allowing the valve to be used when one or more had burned out

4 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 Many of the circuits developed before 1914 were incorporated into the Marconi Short Distance Wireless Telephone Transmitter & Receiver shown here This used the two Marconi valves shown on the previous slide. The T was used as an oscillator in the transmitter (actually a T.N.) and the C as an RF amplifier in the receiver. There was also regenerative feedback. Detection was by a carborundum crystal It might have been possible to adapt this radio for use in the trenches but this was not to be Consequently all the early army transmitters used spark generators and these continued to be used throughout the war Also all the early receivers used crystal detectors. More of this later

5 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 At the start of the war the only radio equipment available to the army were a 500-watt pack set carried by four horses and a 1.5 kW set which required two wagons each drawn by a team of four horses These transportable stations were used at Division and General Headquarters level The transmitters were spark generators and the receivers crystal sets. However, the earlier version of the 500-watt set used a Fleming diode for the detector The design of these two sets go back to about 1911

6 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 Before describing some of the wireless equipment used by the army I want to say a few introductory words about the waveforms from spark sets and continuous wave sets For this I have assumed that the transmitted frequency is 200 kHz The output from a spark set, shown at the top, is a highly damped oscillation occurring at the spark rate, assumed to be 1000 times a second This waveform is noisy and rich in harmonics. It is also a very inefficient way to transmit a signal because of the long gap between each burst of signal The second waveform is a continuous wave, shown unmodulated The third waveform is known as interrupted continuous wave (ICW) where the oscillator is switched on and off as the Morse key is pressed and released ICW radios using valve oscillators began to come into service from late 1916 Continuous waves were also used for speech transmission but this was much later in the war

7 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 The army was slow to adopt wireless sets, but not so the Royal Flying Corp One of their principal tasks was to fly over enemy territory to locate suitable targets for the artillery and for this the crew needed to communicate to the ground Shown here is a small spark transmitter of 30 watts powered from a 6-volt accumulator 600 of these were fitted to aircraft in 1915 The spark gap can be seen inside the open door and the gap was adjusted by the control seen on the right at the top of the box The basic circuit used is shown at the left. The induction coil is a transformer with few turns on its primary winding a large number of turns on its secondary winding The primary circuit has a battery, Morse key and magnetic interrupter. As the key is pressed the interrupter rapidly makes and breaks the current flow to the primary winding This induces several thousand volts into the secondary winding and at their peak causes the spark gap to flash over as the air becomes ionized and providing a low resistance path. This allows a tuned circuit to generate a burst of oscillation which is transferred by the tuning coil to the aerial-earth for transmission The tuning coil can be seen at the front of the set and adjustment for the required wavelength was by wires that clipped on the coil at the required tapping

8 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 Shown here are the waveforms from a spark generator and receiver At the top is the highly damped oscillation produced in the tuned circuit connected to the spark gap This gets stretched out in the aerial circuit as the oscillatory current flow backwards and forwards between the capacitance and inductance The third waveform is that in the receiving aerial The last waveform shows the output from the crystal detector which will be heard as a buzz or tone in the headphones Typically there will be somewhere between 100 and damped oscillations per second

9 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 Shown here is the first set to be used in the trenches and became known as the BF Set It came into service in 1915 and went into action in the Battle of Loos in September 1915 and the battle of the Somme on July 1st 1916 The design of the transmitter was based on that of the No 1 Aircraft Spark set just described The receiver used a carborundum crystal and there were no valves The complete set was powered from a 10-volt accumulator. The total weight, including the aerial with its mast and earth mat, weighed 112 lb (51 kg) and required three people to man it The set transmitted on one of three wavelengths, 350, 450 & 550 metres, but the receiver covered a wider band of 300–600 metres (500 kHz–1MHz) With aerials mounted on masts the range was 4000yd (2.3 miles) but this reduced to 1200yd when the aerial was run close to the ground

10 W/T Trench Set 130 Watt Wilson Transmitter
Division to Corps communication & Corp Directing Station Fixed spark gap with motor- driven 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 This 130-wat transmitter was a ‘big-brother’ of the BF set just described and came into service about the same time in 1915 It was used for communication between Division and Corp and as a Corp Directing Station It had fixed spark gap and a high-speed, motor-driven interrupter to produce a more musical note in the receiver It had the same three wavelengths as the BF Set The communication range was 9000yd, or a little over 5 miles, with the aerial supported on 30ft masts The set was powered from either a 26-volt or 28-volt accumulator In spite of the success of both the Wilson and BF set there were problems of security, enabling the enemy to locate the British army positions There we also equipment failure problems, almost inevitable when new equipment is first introduced

11 Crystal detectors Two types of crystal detectors were used in the receivers: 1. Carborundum, composed of silica and carbon, invented by Dunwoody in 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 Before going on further I want to say a few words about the two types of crystal detectors used in the army radio receivers The carborundum, patented by Dunwoody in 1906, was composed of silica and carbon The Perikon, invented by Pickard in 1909, was a combination of zincite and chalcopyrites Carborundum was more robust but required a bias of 1½ to 3½ volts to provide optimum sensitivity Perikon was more sensitive and had the advantage of not requiring a bias voltage. However, it was more delicate in operation and easily knocked out of adjustment Several army radios had both types fitted with selection by a changeover switch A test buzzer was often included in the radios and used to adjust the crystals and test the headphones

12 Tuner Short Wave Mk. III*
Mk. III version introduced in 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 This tuner was introduced in 1916, although the picture is of the later, 1918 version It covered a wide band of 100–700 metres (429 kHz–3MHz) It was used as a receiver for the Wilson set just described and also for receiving Morse messages from aircraft flying over the trenches It was fitted with both types of crystal detectors The aerial was a 125ft wire laid close to the ground as an inverted L It is believed that 766 of the Wilson transmitter were produced and about 6600 of this receiver

13 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? Continuous wave radios became possible when new and improved valves were developed. The starting point for these was a remarkable valve developed at the French Military Telegraphic Service under the direction of Colonel (later General) Gustav Ferrié A patent application for the valve was made in October 1915 Its construction was very simple; it had a straight tungsten filament, a spiral grid and a cylindrical anode. It was pumped to a low pressure producing a ‘hard’ valve. Known as the French Valve or the TM, it was immensely successful and over 1000,000 were made by the two French companies, Fotos and Métal during the war By 1916 the valve was being manufactured in England by, amongst others, BT-H, the Osram Lamp works of GEC and Edison Swan and was designated the R-valve The basic design was adopted for transmitting valves such as the F, B and AT25. Many variants were also developed for the Navy. One problem with the TM & R valve was the high capacitance between the anode and grid making it unsuitable as an RF amplifier. This led to the low-capacitance Q valve designed by Henry Round, where the connections to the anode and grid were brought out to widely spaced metal caps near one end of the glass bulb The Q valve was intended as a detector but was also used as an RF and AF amplifier The V24, shown below the Q valve, was a later development and intended as an amplifier and played a key role in DF equipment, particularly by the Navy

14 W/T Forward Spark 20 watt “B”. The Loop Set
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 These sets came into service during 1917 and were used for Forward communication There were both Rear and Front Stations and two versions of each one operating on 65 metres (5MHz) and the other on 80 metres (3.75MHz) The transmitter (shown at the left) had a single spark gap, similar the BF Trench Set The receiver had two valves which were either the French TM or the British R They were powered by a 6-volt accumulator and a 32-volt HT battery The Rear Station transmitter and receiver had aerials mounted on 4ft folding tripod supports and an earth mat The Front Station transmitter had collapsible loop aerial 1 metre square and the receiver had a ground aerial consisting of two 35ft insulated wires The communication range was 2000yd Total production quantities was approx each of the transmitters & receivers

15 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 This CW Trench Set, which entered service in 1917, is described in the next two slides The transmitter and receiver were mounted in separate boxes. Transmission was by interrupted continuous waves, which required a heterodyne receiver. Apart from the transmitter and receiver the complete station included a heterodyne wavemeter, a Selector Unit and a 30-watt high tension unit producing alternating current, together with an associated rectifier unit and batteries The complete station weighed 176lb (80kg) in six loads

16 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 manufactured Returning now to the transmitter It came into service in 1917 and was used for Forward Area communication Its rated power was 30 watts and the band covered 450–1450 metres (207 kHz–667 kHz) The earlier Mk III version of the transmitter had a single type B or AT25 valve but this later version, shown here, had two of these valves The aerial had a length of 20 to150ft, depending on the wavelength, supported on masts a few feet above the ground and there was the usual earth mat The minimum range was 4000yd (3.7 miles) The power was supplied by a 10-volt accumulator and dry batteries for the HT. Alternatively the HT could be supplied from an AC unit powered from the accumulator Recorded production was a little under 3000

17 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 manufactured There were also approx Selector Units manufactured Shown here is the companion receiver This has two R valves: The first of these is connected as an oscillator whose frequency is adjusted close to that of the incoming signal These two frequencies are mixed together in the first valve and the output is a low frequency difference signal which is amplified by the second valve before connection to the headphones Approximately 3000 of the receivers were manufactured and there were about 400 of the associated Selector Units

18 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 ft The last set which I am covering today is a radio telephone used in aircraft which was installed in a Bristol Fighter To alleviate the noise from the aircraft engine a special helmet was produced with in-built microphone and headphones One of the objections to speech communication had been the real fear that the enemy could listen in and, for this reason, it was never used for battlefield communication However, using a radio telephone in the plane is more convenient than sending Morse signals, and coded phrases could be used to make it more difficult for the interceptor to understand what was being said This set was fitted to aircraft from mid-1917 It covered the band 350–450 metres (667–857 kHz) and used a trailing wire aerial of length 100–150ft with a lead weight at the end It had a range of 2 miles to other aircraft 15 miles to the ground The receiver had two valves, which were either the B or F. The filament was powered by a 6-volt accumulator and the HT was from a wind-driven generator producing 600 volts

19 Concluding remarks 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 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 onwards when improved valves became available, making possible communication by continuous waves The army was very slow to adopt wireless for communication on the battlefield and relied too much on communication by cable. There was a genuine fear that wireless would be intercepted by the enemy but this was equally true with cable The cable used was being constantly severed by shell fire and the passage of tanks across the battlefield. This meant that important messages could often not be sent Apart from a few high-powered transmitters that played a minor role in the war, the first wireless transmitters were fitted in aircraft during These were used to communicate with crystal receivers on the ground to direct artillery fire The first trench sets went into service in the towards the end of From this time onward the army came slowly round to realizing that wireless communication was a more reliable way to communicate than by cable, particularly when troops are moving rapidly forwards or backwards It was only in the last year of the war that radio communication was universally adopted by the army One is left to wonder how much shorter the war might have been and how many lives not lost if wireless had been adopted in large numbers on the battlefield from 1916 onwards, when improved valves became available, making possible communication by continuous waves

20 Modulation of oscillator to produce ICW
Although probably not the circuit used in the Trench CW set this gives some idea of how modulation would be accomplished if an external alternating voltage source were available At the left is a transformer which applies an alternating voltage between the anode and cathode of the oscillator valve The waveforms below shows what happens When the alternating voltage is positive the high frequency wave builds up to a maximum and continues to oscillate in the tuned circuit when the HT is negative, although its amplitude falls as energy is transmitted by the aerial This repeats on successive cycles of the alternating voltage

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