Page:January 1916 QST.djvu/4

 from 18 to 20 inches in length will be found satisfactory. This little effect shows the remarkable sensitiveness of the Audion when used as an oscillator.

In the sketch, “A” is a tuning condenser of very small capacity. Too much capacity in this place will prevent the system from oscillating properly. A small Murdock variable can be used at “B” and “D,” provided they are well insulated. “C” is another small variable about the same size as “A.” The operator will find “A” and “G” never need a large capacity. The whole secret of getting effective results from this connection is to tune the condenser combination properly. That is, to vary the capacity of the various condensers so that the Audion will oscillate. Once the Audion is generating undamped waves, the set is tuned with the loose coupler and the signals heterodyned. This merely means “beats” are produced. The operator can vary the frequency of the signals at will, as the “beat” frequency depends upon the capacity of the condensers.

OPERATION

The most sensitive Audion bulbs for this work are those which "turn blue" at a telephone voltage of about 30. Bulbs which have this property of using a low telephone voltage, will work well without burning the filament brighter than a cherry red. It is difficult to give precise directions for operating the oscillating valve, but the majority of amateurs will have no trouble with it. In five or ten minutes they will stumble on the proper combination and get far better results than the writer could suggest. IMPORTANT–If the Audion is oscillating properly, a sharp click can be heard in the telephone when the point marked “X” in the diagram, is touched.

RECEIVING

One of the writer’s friends used the instruments described. His station was located on the Atlantic Seaboard. The antenna used was two wires, 200 feet long, and not over 50 feet high at any point. In a series of experiments, no difficulty was found in copying arc stations located at Nauen, Hanover, and Elvese, Germany. Signals sent with the Goldschmidt alternator from Tuckerton, N. J. were also heard. The longest receiving was done when the signals of the Federal Telephone Company’s station at Honolulu, were copied.

Any amateur who carefully reads the suggestion given, should have no trouble operating an oscillating Audion with an aerial of fair length. Amateurs throughout the country are now in a position to receive signals from distances of several thousand miles. The writer hopes the amateurs will write of their experiences as he knows their fellow amateurs will be glad to hear about the results obtained.