STUDIES IN RADIO BROADCAST TRANSMISSION 



151 



its carrier frequency by amplification of the output of a OlO-kc. {piezo- 

 electric crystal oscillator. 



When desired some of the antenna current from the output of the 

 transmitter was rectified and the resulting current was sent over a 

 telephone line to the receiving station so that the frequency and wave 



Fig. 5 — Receiving test station near Riverhead, L. I. showing vertical antenna pro- 

 jecting through roof of building 



form of the modulating signal could be seen and photographed at that 

 point, thus guarding against any possible distortion in the trans- 

 mitter and enabling a direct "before and after" comparison to be 

 made. The telephone circuit was also used for communication 

 between engineers at the two terminal stations. 



At the receiving station double detection receivers and audio fre- 

 quency amplifiers were employed. These did not have entirely 

 "flat" transmission characteristics over the audio frequency band, 

 but in most of the tests this was of no importance. In cases where 

 it affected the results the making of necessary corrections was a simple 

 matter. In tests involving beating the received signals down to audio 

 frequencies through the agency of a local heterodyning frequency, 



