CA RRIER S YSTEM FOR PROGR.I if TR.I NS MISS ION 1 7 5 



figurations to minimize transmission distortion and to give some directional 

 discrimination. 



Frequency translation from the 32-40 kilocycle range of the program on 

 the line to the 80-88-kilocycle range of the program terminal is provided by 

 modulating and demodulating circuits having 120-kilocycle carrier. It is 

 of interest to note that the transmitting 120-kilocycle carrier is supplied 

 through relay contacts which are normally open so that spurious noise and 

 transmission will not interfere with the through program. The relay con- 

 tacts are closed when the blocking filter is in circuit, thus permitting a local 

 program origination only when the through circuit is cut off. 



Relay control circuits have been arranged to coordinate with existing 

 control practices and circuits so that reversibility may be under studio 

 control and network splitting under local control. 



Gain to offset circuit losses is supplied at the output by a transmitting 

 amplifier so that the over-all loss of the through circuit is zero. Patching 

 to spare circuits is thus facilitated. 



In a K2 carrier system^* the transmitting ampUfier has unique properties 

 in that it is self-oscillating at 60 kilocycles at an amplitude which comple- 

 ments the signal amplitude to produce a constant total output power. This 

 feature is used as a carrier system line regulation control, and when a new 

 program originates at the branching point it is necessary to generate another 

 60-kilocycle signal to complement the new total signal output, and to ef- 

 fectively block all 60-kilocycle received from the previous line section. A 

 60-kilocycle BEF is provided for that purpose. 



These branching arrangements, developed for type K systems, have also 

 been adapted for use with type L groups. Blocking and bridging functions 

 are provided as they are for type K and in addition to the complete branch- 

 ing circuits, include simplified arrangements which make use of otherwise 

 idle groups for carrier program circuits without message channels. 



Branching Circuit Performance 



The performance characteristics of the blocking and by-passing circuits 

 are shown in Fig. 6, which represents transmission vs. frequency over the 

 type K range of line frequencies. The solid line gives the normal trans- 

 mission characteristic for through transmission of the program and the nine 

 message channels. The dotted line is the program blocking characteristic 

 indicating 80-decibel minimum suppression over most of the 32-44-kilocycle 

 frequency range. The dashed line is the characteristic effective during the 

 brief interval in the switching process when both branches of the circuit are 

 connected. Its similarity to the other two characteristics is a measure of 

 the effectiveness of the phase simulation over most of the message channel 

 spectrum. Its departure from the other characteristics in the channel 5 



