DELAY EQUALIZATION OF CARRIER CIRCUITS 



187 



To equalize the low-frequency and high-frequency filter delay shown in 

 Fig. 1, a condenser plate of the form shown in Fig. 6 might be visualized. 

 Although the high-frequency delay approximates that desired, the low-fre- 

 quency delay shows insufficient shaping to be complementary to the filter 

 characteristic because of the contribution of the negative-frequency plates. 

 By bringing the plates closer to the frequency axis, that is by decreasing the 

 ratio y^n/oji , a sharper-breaking low-frequency characteristic could be 

 obtained. However, to achieve a sufficiently small delay ripple, the spacing, 

 a, as determined from equation (6) would then have to be decreased with the 

 result that the number of sections would be correspondingly increased. 



In attempting to reduce the total number of sections required, it was 

 observed that a carrier-frequency delay equalizer would not be subject to 



Fig. 7 — Condenser-plate design for a combined carrier and audio-frequency delay 

 equalizer. 



the same low-frequency limitation, since the negative-frequency plates would 

 be removed from the single-sideband signal by approximately twice the 

 carrier frequency of 88 kc. However, since high-frequency delay sections 

 are more expensive to construct than those operating at audio frequencies, 

 a compromise is made in which the first few sections are built to operate at 

 carrier frequencies and the remaining sections at audio frequencies. The 

 equivalent condenser plates, referred to the audio- frequency signal, are 

 shown in Fig. 7. 



A condenser-plate design has thus been achieved which allows the low- 

 frequency and high-frequency delay to be equalized at least approximately. 

 Further modifications must be made in the design, particularly in the 

 middle of the band, to shape the characteristic so that a more accurate 

 complement of the filter delay may be obtained. The delay in a condenser- 



