Interesting Radios of World War 2 – Eric Vast

ITALIAN

The Italians had a most unusual pack set by the thousand in Abyssinia. With it’s batteries it was a somewhat bulky and heavy device giving about one and a half watts in the HF range, each back pack kit being supplied with a box full of quartz crystal resonators. These took the form of a small X cut bar mounted in a glass envelope of the shape of a standard valve, the envelope having a quantity of low pressure neon gas in it. When the TX was switched on and tuned to the frequency marked on the crystal the whole envelope lit up quite brightly. This enabled the not very accurate tuning dial to be set to the exact crystal frequency. Somebody in Abyssinia, after the Italians gave up, decided that these tens of thousands of crystals could be used, and somehow they finished up with me ! Soon I had hardly enough space under cover for them.

Most X cut bars are of high impedance between the usual electrodes and difficult to oscillate. These appeared to be impossible. Normally in its first mode a bar in flexure is mounted at two points each about 0.23 of its length from each end. Such a mounting if the crystal had no electrodes and somehow had been caused to vibrate, would obtain maximum stress in the middle and zero stress near each end. Thus if you apply volts on two small patches near the ends, enough to get it going well, it will act as a voltage amplifier. I suppose these were given to about 10 volts and developed about ten times as much at the maximum points. Neon also lights up much better on HF than on 50 Hz AC as extra ionization occurs. All this adds up to quite a bright light when correctly tuned, for a relatively few milliwatts.

Another curious pack set they had used was very like a meter movement driving a very light variable condenser, which was inside the pack; this was controlled by a little box with a variable resistance which dangled on the operator’s chest. There was calibration on the box and a knob and pointer thing which was rotated to the appropriate mark. It was all rather delicate and must have given a lot of trouble.

UNITED KINGDOM

During the middle of the war our establishment at Cairo was honored by a long visit of the first number 29 sets, under the care of a young man from one of the Army Research Groups. This set was destined to take over from the ubiquitous 19 set of evil memory. Its HF range was the same as the 19 set and the power was roughly the same, but it was FM ! Greatly increased range was hoped for but not achieved. It also had a design fault; on receiving a nearby signal the discriminator de-tuned producing some very curious results. The young man who came with the sets liked our place very much and did his best to stay in Egypt ( from which most of us were trying to get away !) His masters however demanded his return to Blighty. I never heard of him again, perhaps they shot him for not convincing us of the virtues of their design.

GERMANY

The Germans had some very nice numbers indeed, although they were driven in the main by rather inefficient valves. My favorite was a series of roughly 10 by 6 by 8 inch boxes covering a range of 500 kHz to 30 MHz which were of all things TRF and had quite a good sensitivity, certainly as good as a lot of their more usual suprhets. TRf had disappeared years before over the rest of the world, but here were receivers holding their own with the best by sheer good design and attention to detail. The kit one found in the average German tank was also of splendid design. It operated at 30 MHz plus or minus a few kHz and gave out 25 watts. It was full of well made coils of silver deposited on ceramic formers and was more stable in its frequencies than anything I had got in the way of signal generators.

Alas they slipped up the same as we did with the number 9 set used in our tanks. You could not separate the transmitter and receiver frequencies and hence on listening watch both we and the enemy had a battery drain of 15 to 20 amps, which soon flattened the batteries, so much so that the tanks could not be re-started ! At first we just ran out of communications and may well have lost some of the early battles through this. Later converted Bren carriers used to cruise the round with big batteries and a charger, to assist. Still later we did a mod and reduced the listening watch battery drain to about three and a half amps. I often wondered how the enemy coped. I never saw them with any chargers.

We had a very interesting first, although it was not quite a radio but a iFF. These indicators, you may recall, gave out an interrogatory pulse and received a coded answer from a “Friend” and hopefully not a “Foe”. However whenever I flew with RAY Transport Command, they always turned them off as they were very easy to get going enabling the Germans to DF them. One day we received a small box of tricks which had been recovered from by the RAF from the German operated airfield at El Daba.

It had been packed up in a parcel addressed to the Dear Homeland with a covering letter which, when translated said that this highly secret piece equipment had come to them on a Heinkel Night Flier and should never have left home territory. However, when they fled from our lot they left it on the shelf. It seems it was a special design used over the Rhur, when they sometimes put up 500 to 1000 night fighters against a similar number of our bombers. It was full of acorn valves and worked in the 500 to 600 MHz range. It was very particular as to the pulse it responded to and what it answered back. It had a very sophisticated design and I heard later that the Research Group at home were pleased to see it.

A few years ago whilst visiting my son in Australia, I found a translation of a German book on the development of German Night Fighters in the two big wars. A lot of the book was given over to complaints that their very clever development section never got its designs into service. The little device from El Daba got a chapter to itself as one of Germany’s most pressing needs. It seems Hitler himself had to approve all design work, he at first said yes to this device then changed his mind and said,”Try out half a dozen”. Apparently by the time these six were tested facilities for bulk manufacture were not available…. Curious how the answer turned up in a Public Library in a little town in Australia after all these years.

Eric Vast – June 1989

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