WIRELESS SET No. 1


INTRODUCTION
The Wireless Set Number 1, is a transmitter and receiver, intended for portable field station or vehicle operation. It was developed in 1933, for short range Infantry communication, and made by Marconi’s Wireless Telegraph Co. Ltd. The frequency coverage is 4.28 to 6.66 mc/S (70 to 45 meters) in one band, although the knobs are actually engraved 4.2 to 4.8 mc/S. It does not use crystals, but uses a variable oscillator or MO control (Master Oscillator). It can receive and transmit W/T (Wireless Telegraphy) and R/T (Radio Telephony). The W/T mode is now known as CW (Continuous Wave or morse code) and R/T is known as AM (Amplitude Modulation or speech). The manual states that RF (Radio Frequency) output is 0.5 watts W/T. The range is stated as 5 miles W/T and 3 miles R/T, but also says that WS No.1 tests in 1930 showed W/T communication between 215 to 420 miles in daylight. The radio uses external batteries. Contemporary photographs show it on the ground with a top loaded whip aerial, or in an “Austin 7 car”, or a “Truck, 8 CWT, 4 Wheeled Wireless”. This example is dated 1936 and has serial number 751. The WS No.1 was replaced by the WS No. 11.

Figure 1: Front View

LANGUAGE
The manual contains some interesting use of older terms. The control knobs are called “handles” as is the body of the plug used for the headphones and microphone. When the radio requires adjustment or repair, the “Instrument Mechanic” is needed. The circuit has several references which are unusual. Capacitors use the normal symbol “C” unless they are used for bypass, in which case they use the symbol “X”. All the grid resistors are referred to as a “grid leak”. When referring to the aerial, it uses normal spelling in the text, but the drawings use the combined “AE” character, and on the circuit it is “Te” presumably meaning aerial terminal. However the Earth terminals are labeled “EARTH”. The remote control plug for the remote morse key is labeled “S0” probably for socket. Several screws used in the circuit are identified using the character “P” and a number.

The circuit shows some interesting features. The triodes are drawn as expected. The tetrodes are drawn showing the grid as a dotted line, but with the screen grid is drawn as a sawtooth line, similar to the resistor symbol. Perhaps in the 1930s, it was regarded as a true “screen” to stop feedback in this high gain valve (high gain of 111 compared to the triodes gain of 15).

The manual has many paragraphs and some tables devoted to maintenance and fault finding. They mainly deal with a search for loose connections, broken wires, cleaning sockets, and flat batteries. There is little help with actual faulty component identification. The valve testing is covered by substituting valves into the transmitter, and comparing aerial currents to a known good valve.

Figure 2: Circuit

CONTROLS
The front panel is neatly separated into four sections, the receiver on the right, the aerial section in the middle, and the oscillator on the left. Along the bottom is an opening door, that allows access to the valves and the morse key.

The receiver has three control knobs, each with a LOCK and slow motion thumb wheel. Above the two LR PHONES jacks, is the REACTION control which sets the amount of feedback and therefore the receiver gain. This has a 64:1 reduction drive. At the top right hand corner is an EARTH terminal. The knob second from the right, is the DETECTOR TUNING control, which is engraved 4.2 to 6.8 kc/S. This has a 215:1 reduction drive, and is the main station tuning knob. There is also a watch holder on this panel, and it is unusual because it is made of metal.

On the central panel, is the other receiver tuning control which is labeled AE. REC. TUNING and has a 64:1 reduction drive. This is the receiver aerial tuning knob. Above this is the main switch, which turns the radio from SEND to OFF to RECEIVE. Above this is the AERIAL terminal. Next to this is the ammeter which shows the aerial current when transmitting. This is calibrated 0 to 350 mA, and has a weather proof cover. Below this is the TRANS. AE. TUNING control which is for tuning the PA (power amplifier) to the aerial. There is a switch here that selects 2 taps on the aerial coil.

The oscillator section has one main knob labeled MASTER OSCILLATOR and it is spring loaded to prevent backlash. It has a 4:1 reduction gear to drive the tuning capacitor. It sets the transmitter frequency, and has two scales, which cover two revolutions of the knob. Each scale has its own pointer, a RED pointer and a WHITE pointer. Behind the panel is a moving coloured “xylonite”plate. When RED is showing though the indicator hole, the RED pointer is used. Similarly for the WHITE pointer. If BLACK is showing, you are outside of the band. There is a LOCK control, which enables a fine tune knob. Note that it is calibrated in kc/S, rather than METERS. Before accurate frequency calibration, just a 0 to 100 engraved knob was provided, and a chart was used to convert this reading to frequency. Near this is the MICROPHONE jack for a microphone type 3. There is also a switch to select SPEECH or KEY operation.

Figure 3: Back View

MECHANICAL DESIGN
The radio is built in a manner reminiscent of the 1920s era. The central chassis is actually a sheet of black “ebonite” similar to a breadboard or panel radio. The valves and controls are mounted on the front, and the other components and wiring are on the back. There is some progress towards modern practices, in that a sheet aluminium cover acts as the front panel, and protects some components mounted on the front of the ebonite panel. This will also reduce any hand capacity affecting the reaction in the receiver. The ebonite panel is mounted in a metal box, with a removable front lid and back cover. The back cover can be removed to allow access to the wiring and parts. It also has a paper label inside showing the wiring diagram. The front lid is for protection during transit, and is held on by two hooks. It also contains the headphones and microphone. There is a brass plate inside the lid with the circuit engraved on it, and another brass plate has the Operators Instructions engraved on it. The case is made from “copper-iron plymax” material, with iron on the outside, copper on the inside, and brass angle and straps on the edges. It is all soldered together. There are brass internal partitions, between the sections. The case is very heavy, and the whole radio weighs 45 pounds.

Figure 4: Lid

The receiver uses three knobs, and each has a LOCK control. The knob can be turned normally, until the LOCK is tightened. This engages a worm gear behind the panel, and a thumb wheel can be used for fine tuning. The transmitter oscillator uses a different method. It also can be turned normally, until the LOCK is tightened. There are two fingers on the front of the panel, and they engage with an eccentric knob, which uses a cam to rock the knob in either direction to allow a small range of fine tuning. This is mentioned in the manual as being fitted to the “latest Wireless Sets, No.1” so it appears to be an addition the original design.

The wiring is of the old style tinned copper wire covered with spaghetti, and it is all bolted together. You really need a screwdriver, nut driver, and BA spanners to do any wiring changes, or remove a component. The screws are countersunk into the ebonite, and sealed with red paint. Other screws that allow disassembly are cheese head, to differentiate them.

The low value resistors are made from bakelite or fibre bobbins and wound with resistance wire. The RFC (radio frequency chokes) are made the same way, but with normal cotton covered wire. The high value resistors are early carbon types. Before the modern colour coding stripes on resistors, they had a “body tip dot” style, made from a carbon rod with wire pigtails wound on each end. Before this type, each end had a cast solder end, with the pigtails coming from the solder, and a paper label showing the value. Before this style, the solder ends were pointed, and there were no pigtails. The resistor clipped into spring side clips like a fuse, or clipped into end clips like a festoon bulb. There are six of them on the front panel, and it would seem that they were mounted so that they could easily be replaced. Perhaps they were unreliable. The wire wound resistors are on the back of the ebonite panel, and inaccessible without unscrewing the back cover.

Figure 5: Wiring Diagram

The transformers are in closed bakelite cases, as are the tuning capacitors. The fixed capacitors are in sealed metal cases, like oil filled capacitors. The connectors are made of brass pins, in ebonite holders. The two pin 6 VDC plugs are simple round split pins in a square block. The six pin battery plug is clever in that it uses the same ebonite body for the male and female cable plugs, but just uses a different shaped pin. The male pin is a blade. The female pin is a side contact and spring wiper. The sockets on the top of the radio are simple ebonite blocks and protected by a metal cover. The headphone plug is a type No.9 and has a protruding boss, so that only they can be plugged into the headphones jack with corresponding large hole. The microphone plug is a type No.10 with a straight shaft, so only the microphone can be plugged into the microphone jack. Every internal part has the military Broad Arrow stamped or engraved on it.

Figure 6: Front Open

ARS6 VALVE
The radio uses 4 triodes, and 2 tetrodes. The triodes are dull emitter valves, but the tetrode is a bright emitter, using a thoriated tungsten filament. They were first produced in 1927, as the S625, designed specifically for Marconi RF amplifiers. Captain Round designed them by using the filament and grid structure from a DE5 triode, which had a mesh grid. They were manufactured by MOV (Marconi Osram Valve) and originally had a 5 volt filament. Cossor made a look alike version, using an oxide 2 volt filament and called it the SG210. During the 1930s, it was updated with an upright structure from their SG valves, using a spiral wire grid, also using a 6 volt filament. It was called the ARS6 or CV1317. They have a valve socket on each end, and are meant to installed lying down, with the filament and grid at one end of the valve, and the screen and plate at the other of the valve. This reduces the possibility of feedback, and so a high gm i s possible without oscillation. The valve characteristic does have a “tetrode kink” (negative resistance region) so it was possible to break into oscillation at low anode voltages. The 2 valves in this set are Cossor ARS6 valves, acquired brand new in DOD cartons.

For signal isolation, the valves are placed with their filament and grid pins in one section, and their plate and screen pins in another section. An earthed metal partition meets the valve at exactly the point of the inside metal ring structure. The original valve design using the DE5 mesh grid, was across the axial electron stream, and so the “screen grid” could be aligned neatly with a separating partition. The later version using the axial structure from the SG valves, had a radial electron stream, and so the “screen grid” was no longer in alignment. The partition could now only isolate the ends of the valve.

Figure 7: ARS6 valve

ELECTRICAL DESIGN
The radio has a completely independent transmitter and receiver, which requires the separate setting of transmit and receive frequencies. The main switch, turns on the filaments and the HT negative for the receiver or the transmitter. It also turns on the bias for the receiver, and connects the aerial to the transmitter or receiver.

The receiver is powered from the 150 volt supply. It has one RF amplifier using the ARS6 double ended valve, and there is a tuned circuit connected to the aerial by the main switch. On SEND the main switch opens this tuned circuit so that the transmitter does not loose any power into it. This valve has grid bias on it developed from the negative 6 volt supply. The screen has a physically large dropping resistor, and the bypass capacitor is labeled “X6” rather than using the “C” character. The plate goes through an RFC to the supply.

There is a coupling capacitor from the RF amplifier to the grid of the detector. This has grid bias from a tapped resistor across the filament. The detector has a tuned circuit to select the desired station. There is also a feedback winding to the plate. This results in positive feedback which increases the gain. This can be adjusted with the REACTION capacitor, and so control the gain, but too much will cause oscillation. The plate goes through an RFC to an audio transformer.

There are two audio amplifiers, with two inter stage audio transformers and one output transformer. Note that the first transformer has a resistor across the secondary. Also note that the bypass capacitors go to the valve filament, rather than to earth. There is a capacitor across the secondary of the first two, but this is not shown on the circuit. The output transformer is connected to the headphone jacks.

In the transmitter, the oscillator is contained entirely in the left section, separated from the other sections, at the front and the back, by a brass partition. The 2 volt filament in the oscillator valve uses a dropping resistor so it can run from 6 volts. The oscillator is a Hartley type, and the HT is fed into the centre of the coil. The tuning capacitor and trimmer are high quality, and this results in very good frequency stability.

When switched to KEY (for W/T operation), the grid resistor is earthed through the morse key, enabling oscillation. When switched to SPEECH (for R/T operation), the grid resistor is earthed, and the oscillator runs continuously. At the same time, the 6 volt filament voltage is connected through a 20 ohm resistor, to the microphone transformer, and to the microphone jack.

The PA has its filament and grid end of the ARS6 double ended valve in the oscillator section. The filament uses 6 volts. The PA grid is fed by a capacitor from the oscillator grid, not the oscillator plate as I would have expected. There is no intermediate tuned circuit, as it comes directly from the oscillator. The PA grid is connected to an RFC and then to ground through the morse key. The PA is therefore turned ON and OFF by the morse key. When switched to SPEECH, the grid RFC is connected to the secondary of the microphone transformer, and then to the negative 18 volt bias. The bias reduces the PA current to about 70%, and the audio voltage from the microphone transformer adds to the bias and produces AM grid modulation.

The plate of the PA passes through an RFC to the 210 volt battery terminal. A capacitor takes the RF from the PA plate to a variometer which is connected to earth. The variometer is arranged so that for half a turn, the rotor winding is in series with the stator winding. For the other half turn, they are in parallel. This produces an inductance range from 12 to 32 micro henries. The knob is engraved 0-180 then 180-360 to show the position in degrees, and the point of changeover. The aerial is connected through a thermo ammeter, to the top of the variometer, or to a tap on the stator winding. Position 1 (medium tap) is for vehicle operation which corresponds to a “low” resistance aerial. Position 2 (top tap) is for ground operation where there is a “higher” aerial resistance.

The operators instructions state that the aerial current should slightly increase when speaking. If it decreases, then the PA should be adjusted in two ways. The screen voltage can be changed by moving a “wander plug” in the battery box. This can set the screen voltage to four different values, so adjust this voltage so that the aerial current increases when speaking. Also, when the aerial tap is selected and the variometer adjusted, if the aerial current is too high, downward modulation may occur. The manual advises to try retuning and/or using the other tap.

POWER SUPPLY
The radio is designed for battery operation. The LT (low tension) supply is 6 volts. It was made from accumulators and consisted of three 2 volt 16 AH (ampere hour) cells in series, in a wooden carrying case weighing 17 pounds. The manual states that it will last 40 hours. The filament current is 0.35 amps, and is the same when switched to SEND or RECEIVE. When the sender is switched to SPEECH, the microphone draws another 0.1 A.

The HT (high tension) supply is 210 volts. It was made from dry batteries and consisted of nineteen 12 volt units (battery, dry, refill, 8 cell, No.1) in series, in a wooden carrying case weighing 26 pounds. There was a spare battery so there were actually 20 units. The batteries were tapped in several places, and thus provided 210, 150, 90, 0, -6, -18 volts. The negative 18 volt bias uses one and a half units. In addition, the 90 volt tap had a “wander plug” and could be moved, to provide 66, 78, 90, or 102 volts. The manual states that it will last 200 hours. When sending, the radio draws approximately 10 mA at 210 volts, and approximately 2 mA at 90 volts. When receiving, the radio draws approximately 5 mA at 150 volts, and approximately 5 mA at negative 6 volts. The manual spends a great deal of time describing the battery, its layout, its connections, and how to maintain it. The manual also states that the voltages are not critical, and that the radio will still work, when the voltages reduce to 70%.

To operate the radio, the battery must be duplicated, or a suitable power supply designed and built. An alternative, is to use the power supply for the WS No.101. This radio is a copy of the WS No.1 and thus requires the same voltages. It has a vibrator power supply in a similar case, and is powered from 6 volts DC. It develops the same voltages, and even has the same connectors and the same pin connections.

Figure 8: Plugs

AERIAL
The photographs in the manual show a top loaded whip. There are 2 graphs in the back of the manual (Fig 6 and Fig 7) that show the "Field Strength at a Distant Point" verses the type of aerial. The reference on both graphs is a 3 section whip, and this is refered to as 0 dB. Using Fig 7, it shows that reducing the whip to 1 section, produces a -18 dB change. Conversely, increasing the whip to 7 sections, gives a change of +11 dB at the "Distant Point". Figure 6, is for the top hat configuration, and shows progressive increases for a 3 section whip with a 1,2,3 and 4 spoked top hat, giving a maxium increase of +7 dB at the "Distant Point". The top hat is therefore roughly equivalent to a 5 section whip.

REMOTE OPERATION
There is provision for operating the set under remote conditions. One method is having a remote aerial. This is achieved with a remote aerial coupler, type AERIAL COUPLING EQUIPMENT "A" and long wire called CONNECTOR, TWIN, No.15 (15 feet long), with a SET UNIT "A" to match the feeder cable. The set unit only contains a capacitor. The aerial coupling unit contains a variometer and an ammeter. Another method is having a remote operator. This is achieved with two operators and two WIRELESS REMOTE CONTROL UNIT TYPE "A". This is essentially a pair of Field Phones, that allows operator to operator speech, and in addition allows either operator to send CW or speech on the WSNo.1 radio, but the local operator must manually switch from receive to send. It can be connected to a telephone exchange as well.

RESTORATION
The radio was dirty, but otherwise, in good condition. It was missing all its valves. The case needed repainting, but the front panel and inside of the case was in good condition. The components in the back were almost perfect. Everything was cleaned, and the front panel was so good, it was not repainted. Notice that it looks like black wrinkle paint, but it is actually a black “crystal” finish.

Figure 9: Crystal Finish Paint

The missing valves were sourced. The four AR4 triodes were easy to buy, and had an equivalent, which is type 210. The two ASR6 was harder to find, and more expensive. The wiring was checked wire by wire, and was marked off the circuit in red pen. The resistors are of two types. The resistors with values less than 10k ohms are wire wound on bobbins, are mounted on the back of the panel, and were all good. The higher value resistors are carbon type, and are mounted on the front panel in spring clips, which allows easy changing. There are three grid resistors, next to their valve. I went through my box of “ancient” resistors, and found three of the correct physical size (1.5 inches long), shape, and correct measured value. The HT resistors were large (3 inches long), and looked like gigantic fuses. The junk box also yeilded some of those, in the correct physical size and value. These were on the front of the ebonite panel, but under the aluminium front panel. I did not check any of the capacitors, as they were in oil filled metal cases.

Figure 10: Receiver Section

One of the transformers had broken loose, probably due to the radio being dropped at some time. It was removed and the Bakelite case was repaired with epoxy glue. Of the three audio transformers, the two IGRANIC brands had open circuit secondaries, and so I rewound them. They were then bolted back in place. There is actually a capacitor inside each transformer, that is not shown on the circuit. It is probably to modify the frequency response to increase stability.

I checked the filament wiring of the receiver valves, and plugged in three, which are in series. I then slowly brought up the voltage, till I could see the three valves equally sharing the voltage. At 6 volts, I could see the filaments gently glowing. I then applied the HT and brought it up slowly to 150 volts, checking the anode resistors continuously, and the capacitors as well. It all seemed to be working. I fed an aerial through a capacitor to the RF amplifier plate clip, and could actually tune in weak signals. I powered it down, and now plugged in a new ARS6. I then slowly brought up the filament volts again. At 2 volts, it was glowing brighter than the other 2 volt triodes, so I stopped. I went and checked my valve data from 3 sources, and they all said that 6 volts was correct. I insulated the ARS6 filament pin and powered this separately, the other valves were connected to 6 volts. I reluctantly brought up the ARS6 filament to 2 volts again, it was bright, then 3, it got brighter, then 4, it hadn’t burnt out yet, then 5, I could hear signals, and the radio tuned them in well. The reaction worked, there were microphonics, and the sensitivity was about 100 micro volts. The ARS6 valve was still working, so I took it up to 6 volts, it got much brighter and the signals increased dramatically, so it appeared to be the correct voltage!

Figure 11: Receiver Valve Glowing

The radio tuned across the band, the DETECTOR calibration was good, and the REACTION was smooth. The REC AE tuning calibration was off by 200 kc/S, but the manual says that it is affected by the aerial, so different aerials would cause different readings. The dial actually tunes beyond its engraved calibrations, and goes to 7.3 mHz at the high end. I checked the sensitivity for a 10 dB S/N, and it was 5 microvolts on average.

DETECTOR DIAL
FREQUENCY (kHz)		 FREQUENCY (kHz) SENSITIVITY (uV)
end stop 4100 .
4200 4200 8
4500 4500 .
5000 5000 6
5200 5200 .
5500 5500 4.5
5700 5700 .
6000 6000 5.5
6200 6200 .
6400 6400 .
6600 6600 .
6800 6800 5
. 7000 .
end stop 7200 .

I noticed some interaction at 6.8 mHz, when I turned the transmitter tuning knob, it a slight peaking effect, but it was not evident below 6 mHz.

Figure 12: Aerial Section

I now started on the transmitter. The oscillator knob was very stiff, so I disassembled it and applied lubrication until it moved easily but was still firm. The pointers and clamp were adjusted, as they were also rubbing. I plugged in the oscillator valve, and switched to SEND, then slowly brought up the filament volts. The dropping resistor worked, and at 6 volts, there was 2 volts across the valve. I applied HT and brought it slowly up to 210 volts. There was nothing. The morse key contacts were dirty, and after cleaning, the oscillator worked. I checked the frequency with a counter, and it was very stable, and not influenced very much by the oscillator HT voltage. The oscillator starts at 70 volts.

OSCILLATOR
VOLTS		 OSCILLATOR
FREQUENCY (kHz)
70 5008
100 5000
150 5001
200 5001

I checked the dial calibration, but it varied across the band. So I adjusted the trimmer to give a slight positive error across the whole band, and so that at the end stop, it was just above 7.0 mHz, which is inside the 40 meter Amateur band.

OSCILLATOR DIAL
READING (kc/S)		 ACTUAL
FREQUENCY (mHz)
end stop 4020
4200 4201
4500 4508
5000 5024
5200 5223
5500 5532
5700 5729
6000 6026
6200 6220
6400 6418
6600 6612
6800 6806
end stop 7010

The aerial thermo ammeter was open circuit, so I replaced it with a 350 mA meter that I had previously repaired. The glass cover was discoloured, but attempts to clean it failed. I now plugged in the PA valve, another expensive ARS6. I brought up the filament volts slowly, and it glowed brightly as well, but with no ill effects. I slowly applied the 210 volts HT and the 90 volts to the screen. It all seemed well. I added a dummy load and a watt meter, and tuned up. This gave a reading on the aerial current ammeter, and showed 0.3 watts on the watt meter. After testing several components, measuring voltages, checking the drive with the oscilloscope, I could not get the stated power of 0.5 watts. So I substituted some valves. The ARS6 made no difference. Replacing the AR4 triode oscillator brought the aerial ammeter current up to 220 mA, and the power to 0.7 watts. The tuning was quite sharp, and it exceeded the 0.5 watts quoted in the manual.

I switched to SPEECH and the power dropped to 0.35 watts. The modulation envelope on an oscilloscope looked a little distorted, so I followed the manuals recommendations. I changed the screen voltage from 70 to 110 volts, but while this changed the power output by about 0.1 watt, it made little difference to the distortion. I then changed the PA grid bias from -20 to -10 volts.

PA GRID
BIAS (V)		 PA
OUTPUT (W)		 MODULATION
DEPTH (%)
-20 0.3 60
-18 0.34 .
-16 0.38 .
-14 0.4 .
-12 0.45 .
-10 0.5 30

While this changed the power output and modulation depth, the distortion only got worse at -10 volts. I tried detuning the plate circuit as the manual suggested, and this lowered the power output, and vastly reduced the distortion. So this was the answer.

Figure 13: Transmitter Section

PERFORMANCE
The receiver works quite well, producing a sensitivity of about 5 micro volts for a 10 dB signal to noise. It reaches the 40 meter band. It can easily receive AM signals, and can also receive morse and SSB signals, by using the REACTION as a beat note generator. SSB can be resolved by setting the REACTION to oscillate, and then using the thumb wheels to tune the station. There is a slight drift up and down.

The controls are easy to use, but suffer from the older tuning method, where two knobs have to be set to the same frequency, because they are not ganged. The AERIAL tuning is first set to the required frequency, then the DETECTOR tuning selects the station, and then the AERIAL is readjusted for maximum volume. The set may break into oscillation at this point so the REACTION needs to be adjusted again. After a while you get used to tuning the frequency with two knobs, then slightly adjusting the REACTION for more volume, or to reduce oscillation. The three controls can be locked with the LOCK screws, and then fine tuning can be done with the thumb wheels. There is operator fatigue, because static crashes, sudden oscillation, and some spontaneous clicks, are very loud and seem to go straight through your head. The microphonics from the valves are not a problem. Detuning the receiver frequency by proximity of the operators hands, is minimal, as all the components are under the aluminium front panel. There is a slight frequency pulling, as you adjust the REACTION when near oscillation.

When the REACTION is close to oscillation, the frequency bandwidth is quite narrow, but it broadens as you reduce the reaction. The bandwidth was measured and a graph was drawn. This is the method used. The receiver was tuned to a signal, adjusted for maximum sensitivity, and the audio output measured. Then the input signal was increased, which required the REACTION to be reduced to provide the same audio output. The graph shows how the bandwidth gets broader as the REACTION is reduced. For three sensitivities of 5, 15, and 25 micro volts, the -3db points show a corresponding bandwidth of 2, 6, and 10 kHz.

Figure 14: Bandwidth Graph

The transmitter is simple to tune, is stable, and can give good CW and AM transmission. The tuning has to adjusted, for good AM modulation. The SEND/RECEIVE switch only powers up the transmitter or the receiver, so it is difficult to set the transmitter to the same frequency as the receiver (netting). However, the calibration is very good, and the receiver broad enough to enable hearing the remote transmitter, and then adjusting the receiver to the remote sender frequency. This is acceptable for working between two stations, but may be difficult for multiple stations.

IMPROVEMENTS
The radio could be improved. A switch position or a button could be added to enable only the oscillator, to allow netting. The oscillator LOCK and fine tune could be made the same as the receiver controls and use a thumb wheel. There is a bakelite plate for the headphones, which will prevent marking the panel. The microphone does not have this, it just has a hole, so it could be improved by adding a plate which will protect the front panel. The multiple earth screws, lugs and tags, could be grouped or joined with an earth wire. This would improve earth resistance and remove possible high resistance joints. A power supply could be made which runs from 6 volts DC and provide the multiple voltages required. This would make vehicle use and ground use much easier and simpler, and do away with the HT battery.

REFERENCES

SIGNAL TRAINING, VOLUME III, PAMPHLET No. 15, WIRELESS SET, No.1, 1938

Copyright by Ray Robinson VK2NO

INDEX