628 BELL SYSTEM TECHNICAL JOURNAL 



additional networks which were, for convenience, of identical design. 

 The results obtained by using one, two or three of these networks were 

 made to correspond, respectively, to three assumed weather conditions 

 which may be designated semi-wet, wet, and extra-wet. These three 

 conditions were determined upon the basis of the range of leakage 

 conditions which exist on open-wire lines under different weather 

 conditions. 



The attenuation equalizing and phase correcting networks for one 

 of these steps are illustrated in Fig. 7, while the computed attenuation 

 and phase delay obtained by the use of the three different steps of 

 weather correction are shown in Figs. 3 and 4. 



The networks described above are of the "constant-resistance" 

 type, whose characteristic impedance is a pure resistance at all fre- 

 quencies.^ These networks are designed to be connected in series. 

 The methods used in the design of the networks involve a large amount 

 of mathematical theory, a discussion of which is not necessary for the 

 purposes of this paper. 



Synchronizing and Voice Circuits 



So far the discussion has dealt only with the problem of trans- 

 mitting the television currents. In addition to this, there is required 

 the transmission of voice currents and of synchronizing currents. 

 It is entirely feasible to transmit these currents together with the 

 television currents over a single circuit. However, for the purpose of 

 simplification, separate facilities were employed in the television 

 experiments for picture, voice and synchronizing currents. 



The diagram in Fig. 2 shows the circuits which were actually pro- 

 vided for the demonstrations. It will be seen that in addition to 

 the two picture or television circuits, there were provided a syn- 

 chronizing circuit, a four-wire "program" circuit, and an order 

 circuit. 



The method of synchronizing the sending and the receiving machines 

 has already been described in the paper by Mr. StoUer. It requires 

 two currents, one having a frequency of about 18 cycles and the 

 other about 2125 cycles. In order that an ordinary telephone circuit 

 might be used for this purpose, the lower frequency was made to 

 modulate by means of a telegraph relay, a carrier current having a 

 frequency of about 750 cycles per second. An amplifier-detector 

 at the receiving end of the synchronizing system demodulated the 

 750-cycle current, delivering 18 cycles to the television apparatus. 



The requirements for the synchronizing circuit were that it must 



3 Partially described in U. S. Patent No. 1,603,305 to O. J. Zobel. 



