ADVANCES IN CARRIER TELEGRAPH TRANSMISSION 189 



As will be seen by reference to Fig. 13B there is a marked frequency 

 effect; the variations becoming greater for the higher frequency 

 channels. This is particularly noticeable where there is a large number 

 of channels operating simultaneously, as otherwise individual varia- 

 tions between channels tend to obscure the gradual trend. 



Figure 14:A shows the marking interference, expressed in db, due to 

 changing from one channel marking to all channels marking for various 

 changes in repeater output ranging from 2.2 to 22.2 dbm. and a fre- 

 quency range extending from 425 to 4335 cycles. 



-2 2 4 6 8 10 12 14 16 18 20 22 



NOMINAL POWER AT REPEATER OUTPUT (DUE TO 12 MARKING CHANNELS) IN dbm 



Fig. 15 — Spacing interference. H44 circuits. Interfering channels operating. 

 12 channel system. Channel No. 5 (1105 cycles per second). 



Figure 14JB shows the reduction in received current which results 

 on any given channel over the same range of conditions as Fig. 14^1 

 except that in this case the associated channels are transmitting 

 uncoordinated reversals. 



