RADIO EXTENSION LINKS TO TELEPHONE SYSTEM 645 



oceanic path at the lower angle. Beneath this row of phase shifters 

 is indicated a second set connected in parallel with the first set. The 

 second set is adjusted somewhat differently so that the receiver in 

 branch B will receive signals over the path with the higher angle as 

 indicated by the solid line directive pattern in the neighboring diagram. 

 The two separate signals may therefore be separately received. 

 Since, however, they do not arrive at identical times they cannot be 

 added without producing distortion. By interposing a delay in the 

 output branch of the one arriving earlier, which in this case is branch 

 A, they may be added directly into a single audio output. In this 

 case if one branch fades the other will continue to receive the signal, 

 and while both are receiving a better signal-to-noise ratio obtains. 



A cathode ray oscillograph is connected on the outputs of these 

 receivers as indicated in the diagram so as to indicate when the delay 

 is satisfactory for adding the two signals in phase. 



As mentioned previously the direction from which a signal comes 

 may change from time to time. In this case a fixed adjustment of 

 the phase shifters may allow the signal to disappear. The operator 

 needs to be ready to change the phase shifters when necessary but it 

 is also desirable that he change them in the desired direction without 

 interfering with the conversation arriving over the circuit, which 

 means he should be able to adjust them without using cut-and-try 

 methods of adjustment. To accomplish this a third set of phase 

 shifters is provided which are continually driven in rotation by a 

 motor so that as they rotate they cause the direction of the signal 

 received by a monitoring receiver to shift its angle of reception over 

 the entire angle range at which signals might arrive. The output of 

 this receiver is connected to two plates of a cathode ray oscillograph 

 Avhile to the other two plates are connected potentials from a rheostat 

 on the phase shifter drive shaft so that the potential will be indicative 

 of the position of the phase shifter. If the phase shifter continually 

 rotates the varying signals will cause the varying deflection in the 

 vertical direction and so draw a pattern as indicated in Fig. 23, which 

 will show immediately by suitable calibration the angle between the 

 two different signals. The operator may thereby adjust his phase 

 shifters by calibration and without cut-and-try tuning. 



Inasmuch as the rhombic antenna does not operate with standing 

 waves and may be used for a variety of frequencies it may be used 

 simultaneously for this variety of frequencies. The transmission lines 

 from the rhombic antennas to the phase shifters also operate without 

 standing waves so they likewise may operate simultaneously at a 

 variety of frequencies. It is thus possible by connecting other phase 

 shifters and other receivers to utilize a single row of rhombic antennas 



