Unbelievably Simple Set Actually Works Well for Local Stations
One of the war's wonderful gadgets undoubtedly was the "foxhole radio receiver" designed by Lieut. M. L. Rupert while he was attached to an infantry outfit serving on the Anzio beachhead in Italy.
If you want to make a set that is so simple as to be almost unbelievable, and that costs virtually nothing beyind the price of a set of earphones, here's your dish.
ALL you need for the set is a razor blade of the "blue" type, a safety pin, a cardboard or wood cylinder two inches or more in diameter and any small cotton-covered wire, such as No. 28 or 30, for the 120 turns on the coil. Such a coil has sufficient turns of wire to pick up a station without other tuning aid. Ordinary nails, provided they are not rusty, can be used as binding posts for wrapping the connections.
In the Lieutenant's own words, here's how it works:
"The razor blade is tacked down with a wire tapped to it and going to one side of the coil and onto the aerial. The other side of the coil goes to the ground and to one side of the head set. From the other side of the head set a wire goes to the safety pin, whieh is driven into some wood at one end so the pin may be turned. Then the free end of the pin is moved across the unground part of the blade and in that way you can find your station."
Engineers of one of this country's major broadcasting companies promptly constructed a set according to the Lieutenant's specifications, and found that it worked! They did, however, make one improvement, by breaking off the end of a lead pencil and wiring it to the movable end of the safety pin, where it is used for contact with the blade. This was found to result in a decided increase in volume.
You will find that considerable patience is required in finding the most sensitive part of the blade for the pin point or pencil point. Avoid the portions where the trade name of the blade is printed. A couple of light scratches made on the blade with a nail file will be found helpful. And the longer the aerial, the better the reception, with best results, of course, being secured at night.
The circuit is similar in principle to the ordinary crystal set, the suggested combination fulfilling the function of the galena rock and cat's whisker.
Lt. M. L. Rupert's "foxhole rodio," used on the Italian front, gets reception on a raior blade. The chief engineer of a major broadcasting company improved it by tying pencil lead to the pin point. Wire gauge is not critical, but good headphones, a long aerial, and patience in locating a sensitive spot on the razor blade are all requisite