APPLICATION or WIRE TRANSMISSION TO RADIO 133 



Transmission Levels on Combination Wire and Radio 

 Telephone Systems 



It will be of interest to trace thru the approximate transmission 

 levels which obtain for a radio system linked up with a long repeat- 

 ered land line system. 



In Fig. 6, there is taken a rather striking example of this case in 

 the transcontinental telephone line as connected up to radio ex- 

 tensions at its termini — to Catalina Island on the Pacific and to a 

 vessel at sea on the Atlantic. The transmission illustrated is that 

 occurring from east to west. The voice currents start out from the 

 vessel at zero level, are amplified to a relatively high level and upon 

 being transmitted to the shore 150 miles (240 km.) away, drop to a 

 very low level. At the shore radio station they are boosted up, at 

 New York amplified again, and put upon the transcontinental circuit. 

 Regularly at about 300 miles (480 km.) the telephone repeaters pull 

 back the transmission level to about its original value. In the radio 

 link at the w-estern end the currents are again amplified to a high level 

 at the transmitting station, drop down to a very low level at the re- 

 ceiver and are brought back to a level at which they can be heard. 

 Actually in the receiving telephone the transmission is about logio 



— = 1.2 below zero level, or roughly 25 miles of standard cable 



" down." The total loss and the total gain in the circuit is enormous, 

 as is shown by the figures given in the diagram. This is a rather 

 striking illustration of the extent to which amplification properly dis- 

 tributed and maintained can be used to overcome attenuations enor- 

 mous in the aggregate. Just to give a better idea of what these values 

 of attenuation and amplification mean, it may be noted that were it 

 necessary to supply at the transmitting end all of the amplification re- 

 quired for delivering this volume of transmission to the receiving end 

 thru the combination circuit, the kilowatts required would be measured 

 by a twenty-nine place figure, an amount of power unavailable in 

 the world. The importance of correctly distributing the amplifica- 

 tion along the system is well illustrated by this figure by comparing 

 it with the signaling power actually represented in the system, which 

 sums up to something less than 1 kilowatt. The difference is simply 

 a question of the transmission level at which the amplification is 

 worked. 



Fig. 7 gives a view of the interior of one of these radio telephone 

 stations of the American Telephone and Telegraph Company and 

 Western Electric Company. It is located at Deal Beach, New Jersey. 



