TRANSOCEANIC TELEPHONE SERVICE 283 



cycles then passes through a combination of amplifiers and filters which 

 further exclude the unwanted interference. The wanted signal reaches 

 the second detector where it is demodulated and the voice currents 

 reproduced. The latter are then amplified and applied to the telephone 

 lines. 



A portion of the output from the intermediate amplifier which would 

 normally go to the second detector grid, is diverted and further am- 

 plified. It is then supplied to a device which automatically tends to 

 maintain the receiver output volume constant by controlling the bias 

 potential of the first detector grid circuit. The time constants are 

 adjusted so that this gain control does not respond to the normal varia- 

 tion in signal power corresponding to speech modulation. Otherwise 

 of course, there would be serious distortion effects. This device 

 partially offsets the ill effects of wide fluctuations in signal intensity 

 but it does not overcome the deterioration in signal quality which 

 usually accompanies the low field strengths during such fluctuations. 



Receiving Equipment 



At the receiving station the apparatus for each channel comprises (1) 

 the radio receiving set, (2) a power plant for the receiver, (3) wire 

 terminating equipment and repeaters. The latter are located at a 

 central point in the station along with certain voice frequency testing 

 apparatus used in common by all channels and supplied with power 

 from a common source. 



A radio receiving set which embodies the above described system and 

 of the type installed at Netcong is shown in Fig. 8. It consists of a 

 large number of individually shielded units mounted on panels and 

 assembled on three self supporting racks of the type commonly em- 

 ployed in the telephone plant. This permits the use without modifica- 

 tion of certain standard pieces of equipment, such as jack strips, fuse 

 panels, meter panels, audio frequency filters, and the like. It also 

 permits the removal and repair or substitution of units with a minimum 

 of delay. The set is required to receive signals at three fixed frequen- 

 cies in the range 9000 to 21,000 kilocycles. This involves connections 

 with three antennas through three separate transmission lines. The 

 tuning of the antenna and transmission line terminations are rather 

 lengthy processes requiring precise adjustments. In order to facilitate 

 quick changes from one operating frequency to another without intri- 

 cate tuning operations, the first stage of radio amplification is provided 

 in triplicate and the switching is done between the first and second 

 stage. Thus the antennas are permanently connected to the set and 

 their adjustments remain undisturbed. The circuits of the second 



