574 BELL SYSTEM TECHNICAL JOURNAL 



Studies are now under way looking toward systems which will 

 compress the volume range transmitted over the line and expand it 

 at the far terminal, but possible applications to radio systems may be 

 difficult since receiver characteristics need to be considered. 



If some volume range compression and expansion system is not 

 employed, ability to handle a materially wider volume range can only 

 be obtained with considerable difficulty. In the radio part of systems 

 it will require reductions in radio transmitter noises and involve loss in 

 the effective range of radio stations, unless higher powered transmitters 

 are employed. In the wire part of systems it may involve the use 

 of amplifiers and loading coils capable of handling more power, means 

 for materially reducing the crosstalk coupling between circuits and also 

 means for making the program transmission circuits more quiet. 



Description of New Cable System 



In this program transmission system the nominal telephone re- 

 peater spacing of 50 miles, common with message telephone circuits, 

 is retained. The pilot-wire regulator system which compensates for 

 changes in transmission caused by temperature changes in message 

 circuits is also used for the program circuits.* The diagram in the 

 top part of Fig. 3 shows several hundred miles of program transmission 

 circuit, illustrating how it is divided up into repeater sections and 

 pilot-wire regulator sections and also indicating the principal pieces of 

 equipment located at the repeater stations. 



As indicated on the diagram of Fig. 3, there are two classes of 

 repeater stations, known as regulator stations and non-regulator sta- 

 tions. At the non-regulator stations the repeater gains are maintained 

 at fixed values while at the regulator stations they are varied under 

 control of the master pilot-wire regulating mechanism in such a way 

 as to compensate for the transmission variations of the cable con- 

 ductors caused by temperature changes. 



At each non-regulating repeater station are placed: 



1. An attenuation equalizer which corrects for the attenuation differ- 



ences at different frequencies (at average temperature) intro- 

 duced by the preceding repeater section. 



2. A delay equalizer which corrects for the difference in delay at 



different frequencies introduced by the preceding cable section. 



3. A one-way amplifier introducing sufficient gain to overcome the 



line loss, together with the added losses introduced by the 

 attenuation and delay equalizers. 



^ A. B. Clark, "Telephone Transmission Over Long Cable Circuits," A. I. E. 

 E. Transactions, Vol. 42, Feruary, 1923. 



