EXPERIMENTAL TRANSVERSAL EQUALIZER FOR TD-2 1439 



The coupler in Fig. 5 represents any one of the taps on the line PQ 

 in Fig. 3. The signal emerging from Port 4 can be written as E£^"''^^^\ 

 where 5 is a time delay dependent on the location of the tap on the line 

 PQ. The signal emerging from Port 3 is then p£'f:"'"""'^*\ where p is the 

 voltage reflection coefficient at Z, and is given by 



_ R — Ra 

 ^ ~ R + R,- 



Here R is the value of resistance used to provide the impedance Z, and 

 Rq is the impedance seen looking into Port 4. An examination of the 

 signal from Port 3 shows that it is the same as the signals Ca or Cb in Fig. 

 3, with the reflection coefficient p substituted for variable Ka or Kh in 

 Fig. 3. Thus, it is seen that we may use the reflection at Z, variable by 

 controlling the value of /?, to perform the function of the box K in Fig. 

 3. Neglecting parasitic losses we may then write: 



jjr R — Ro 



K = p = 



R -\- Ro 



and 



^ = ^0 ^-^. (5) 



This gives us the value of R to use for any desired value of K for any of 

 the taps which derive echos, assuming the summing circuit has equal 

 attenuation in all paths. In the case of the main central tap, the signal 

 from Port 4 of the coupler is seen to be the same as the main signal eo in 

 Fig. 3, and is used as such directly. 



VII. METHOD OF ADJUSTMENT 



The detailed design of a manually adjustable eciualizer is materially 

 influenced by the method to be used in the field for determining the 

 setting of its controls. The present equalizer with 14 independent con- 

 trols would present a complex problem of field adjustment unless special 

 procedures were developed to simplify the adjustment. To adjust the 

 equalizer, the radio circuit being equalized must be taken out of com- 

 mercial service, so any reasonable measures to simplify the adjustment 

 or reduce the time reciuired are justified. 



Two methods appeared to be feasible at the time the de\elupment 

 was started. One would be to use existing gain and delay sweep test 

 circuits. These present a visual display of the circuit gain or delay dis- 



