UL TRA -SIIOR r- WA VE PROP A GA 7 'ION 



271 



When the receiver was at Berkeley and Stuart Streets it was possible 

 to employ the usual method of calibration ^^ because the roof was flat. 

 With the receiver at the Seaverns Street location, however, the gabled 

 roof made it impractical to support the standard field generator 

 opposite the midpoint of the antenna. In the latter case, accordingly, 

 the constancy of the gain of the receiving equipment was depended 

 upon in reducing the measurements to field strengths in absolute 

 units. This lack of calibration did not introduce a large uncertainty, 

 since the receiving equipment has been used over a period of years 

 during which time its gain has remained constant within a few decibels. 



Two-Way Tests 



At the conclusion of this survey, actual two-way tests were made 

 between a cruising car and fixed locations. For this purpose a car 

 was equipped by E. B. Ferrell and R. C. Shaw ^^ with an ultra-short- 



Fig. 13 — Fixed terminal transmitting equipment located at Berkeley Street. 



wave transmitter and receiver arranged for simultaneous two-way 

 communication. A distinctive feature of this equipment was the use 

 of a single antenna for simultaneously transmitting and receiving. 

 This was made possible by the use of a suppressor circuit in the re- 

 ceiver to prevent overloading of the first detector by the outgoing 

 signal. With this suppressor circuit, which consisted of only a half 

 '-' Both of Bell Telephone Laboratories, Deal, New Jersey. 



