EXPERIMENTAL TRANSVERSAL EQUALIZER FOR TD-2 1443 



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Fig. 9. — Summing network with cover removed. Main signal input is at right, 

 echo signal inputs on top, and output is at left.. 



stead, a resistance summing network was developed using deposited 

 carbon resistors. An L-pad is used in each echo path and a series resistor 

 is added to the main path to preserve the 75-ohin impedance level, intro- 

 ducing a main path loss of about 0.4 db per tap. A model with cover 

 removed is shown on Fig. 9. The main signal is introduced at one end 

 of the structure, the echo voltages are connected along the side and the 

 sum is taken off the other end. The return loss measured at any of the 

 connectors with the others terminated was of the order of 40 db over the 

 60- to 80-mc band. 



An attentuation equalizer is required to make the transmission through 

 the main path constant. This path consists of about 108 feet of 728 cable, 

 the straight -through loss of six couplers, and the coupling loss of the 

 main coupler. The net distortion over the band is a slope of about 1.5 

 db and is corrected for by a constant resistance ec^ualizer. Return losses 

 exceeding 34 db were obtained over the frequency band. 



X. ASSEMBLY 



All the components were mounted on the rear of a standard i-elay rack 

 panel. The rheostat controls are arranged on the front of the panel as 

 shown on Fig. 10. This is a front view of the completed eciualizer. The 

 controls for the leading echo terms are on the left and for the lagging 

 echo terms on the right. They are arranged vertically in numerical order 

 with the first terms (shortest time separation from the main signal) at 

 the top. 



The rear of the panel is shown on Fig. 11. The directional couplers 

 are mounted horizontally in two vertical columns. The cables forming 

 the delay line sections are terminated in a plug and a jack and these are 

 inserted in successive couplers, from the second port of one to the first 

 port of the next. The third port of each coupler is connected through a 

 short cable to its corresponding rheostat assembly. The fourth port of 

 each coupler is connected to the summing network. An exception is 



