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. 



