WIRELESS TELEPHONY — SLAUGHTER. 183 
AIRPLANE SETS. 
At the outset of the war-time development work on the airplane 
wireless telephone apparatus the requirements which the apparatus 
would have to meet and the particular conditions under which it 
would operate were largely unknown; this information became ap- 
parent more or less gradually during the progress of the development 
work, which fortunately proceeded along such lines as to substan- 
tially comply with the requirements as they developed. As originally 
conceived, these requirements may be briefly stated as follows : 
The apparatus should be capable of effecting reliable 
telephone communication between two airplanes at distances 
up to 2,000 yards. 
The weight of the apparatus should be the minimum pos- 
sible consistent with meeting the range requirements and 
other conditions imposed on the operation. 
The apparatus should be of the simplest possible construc- 
tion and should require the minimum amount of adjustment 
or manipulation by the aviator. 
It was realized that special conditions would be encountered on the 
airplane which would make the development work extremely difficult 
and would require radical departures from any previous practice. 
Among these special conditions may be mentioned the tremendous 
noise and vibration created by the engine and wind, the necessity of 
reducing the fire hazard to a minimum, and, above all, the extremely 
essential condition that the wireless telephone apparatus must create 
the minimum possible interference with the various other functions 
of the aviator. 
The various elements comprising the complete Avireless telephone 
set may be grouped into the following units: Power plant, trans- 
mitting unit, receiving unit, antenna system. 
The details of these various units and the problems encountered 
in their development are briefly described in the following para- 
graphs : 
POWER PLANT. 
The preliminary experiments with various types of apparatus soon 
determined the power requirements of the apparatus which included 
power supply for the filament and plate circuits of the vacuum tubes 
for both transmitting and receiving circuits and power for the tele- 
phone transmitters. The filament power required was determined 
to be 1.35 amperes at 24 volts and the plate circuit power for the 
transmitting set 0.070 amperes at 275 volts. The plate current for 
the receiving tubes was extremely small, namely, less than 0.004 
amperes, and it was decided to furnish this power from dry batteries. 
