Page:Popular Science Monthly Volume 88.djvu/325

 Popular Science Monthly

��297

��weighs between 75 and 100 pounds. An installation which I have been supply- ing the United States Government for aeroplane work, weighs 60 pounds. Yet here we have a complete apparatus weighing but 2y pounds.

It would be practically impossible for one to build such a set in this country for government use because the govern- ment tests would automatically elimin- ate the instrument itself. For example, the generator if run under ordinary con- ditions in a room would not stand up under fifteen minutes' continuous use. The United States Government insists on a test of eight hours' duration in a closed room. The French and English have wisely concluded that since the generators are used in an aeroplane travelling through air at the rate of sixty miles an hour, a cooling effect is obtained which may be utilized and which will simplify the task of the radio designer. This generator seems to work most satisfactorily and ought, it appears, to be employed by our own navy for aeroplane work. On one end of the shaft of the motor is attached a rotary synchronized spark gap. A small closed-core transformer mounted in a fibre tank full of oil and generating about 20,000 volts is included in the secondary. The condenser used is of the Dubilier type. This is the standard for aeroplane installations in Europe for the Allies.

The condenser is the most important element of the aeroplane wireless in-

����Fig. 4. The small apparatus used mainly by the French for directing artil- lery over trenches. This apparatus weighs about 12 lbs. and is capable of utilizing about 40 watts

��Fig. 5. A 750 watt equipment on aeroplane using the resonance alterna- tor of J. Bethenod. This alternator generates an alternating current of 1500 cycles, 750 watts, at a speed of 4500 R.P.M. The outfit consists of a gen- erator, a transformer, oscillating circuit and a system of manipulation. The generator complete weighs but 42 lbs., and is built for an overload of 20^,^. It is driven by the motor of the aeroplane. The transformer has a closed core, and is air cooled without magnetic leakage. The oscillating circuit provides for op- erating on a wave length up to 600 m., and is self-excited by a condenser with 0.01 M. F. capacity

stallation ; for it is obviously impossible to use fragile Leyden jars. The con- denser must be unbreakable, have high efficiency, and occupy very little space. Figure 2 shows such an installation.

By means of a small aeroplane aerial it is possible to radiate one ampere with this installation. Communication can be held over distances of fifty miles. The English government is building its own installations along these lines.

Duplex Wireless Telegraphy.

DUPLEX wireless telegraphy, in which two messages are simul- taneously sent in opposite directions between two radio stations, is entirely practical. The system is used between Glace Bay and Clifden, and in the trans-Pacific stations. This arrange- ment makes it possible to handle twice as mn.ny radio messages between two stations in a given time.

�� �