166 



BELL SYSTEM TECHNICAL JOURNAL 



loss (it was actually in miles of standard cable) until the indicator 

 reading is the same as that obtained from the radio receiver. The 

 setting of the variable network then indicates the transmission loss 

 of the circuit. The method is similar to that developed for measuring 

 the transmission loss of telephone circuits. 



These measurements were used for the purpose of enabling the 

 radio link to be worked to a contsant transmission equivalent — in 

 this case, of about six units. The procedure for so doing was as 

 follows: When the vessel was first picked up, the receiving amplifica- 

 tions in both east and west channels were adjusted until the measure- 

 ments showed a transmission equivalent of 6 units. Then as the 

 vessel proceeded on her course the transmission equivalent was 



MEASUREMENTS OF TELEPHONE TRANSMISSION OF RADIO CIRCUITS 



| Transmission MeasuringUnitI 



Loss Y~ 



IQ OCPGen erator Net 



-J~ H — I I — | | — I 



Transmitter ■"t 



om 



Measuring Net 



I *c 



DEAL BEACH. N.J 



Repeater LossNet RadiL 

 Receiver 



Fig. 13 



I I 



SS GLOUCESTER 



measured at intervals of an hour or less and the receiving amplifica- 

 tion readjusted to hold the desired six-unit equivalent. In this 

 way the talking efficiency of the radio link was kept constant. 



The total amplification change which had been made from the 

 beginning of a run up to any one time gives a measure of the change 

 which has occurred in the transmission loss of the radio circuit. By 

 plotting this change in relation to the time of day and in turn to the 

 varying distance between the two stations, an interesting curve 

 results which shows the manner in which the progress of the vessel 

 affects the transmission of the radio circuit. In Fig. 14, the time of 

 day is plotted horizontally, distance is plotted vertically on the right 

 and amplification vertically on the left. The zero amplification 

 reference is the amplification in the circuit which gives a six-unit 

 equivalent at the time the vessel is first picked up. 



