448 



REGULATORY CIRCUITS 



Nichols chart is shown in Fig. 8-33.^^ Note that if the corner frequency in 

 Fig. 8-32 had been a double corner, C03 would be doubled; if it had been a 

 triple-corner frequency or equivalent, cos would be tripled, etc. However, 

 Fig. 8-33 would be essentially the same in the crossover frequency region. 

 This example illustrates one method of synthesizing the search control loop 

 directly with a minimum of the usual cut and try effort. The procedure is 

 similar, even if other criteria are used to specify the search loop perform- 

 ance. 



8-29 SEARCH LOOP MECHANIZATION 



Actual circuit details of search loop mechanization cannot be discussed in 

 general terms because the control loop components vary with specifications, 

 with the nature of the power available, and with the antenna size. How- 

 ever, a few general considerations can be discussed. 



The basic components needed to mechanize each of the two search loops 

 are shown in Fig. 8-34. The coordinate converter needed to correct the 



Loop Input Signal Corrected 

 'for Aircraft Space Motion 



-r 



Power 

 Amplifier 

 Modulator 



Actuator 



I Possible 



I Tachonneter 



■E>- 



Fig. 8-34 General Block Diagram of Search Loop (One Channel). 



input signal for aircraft motion is not shown because it was discussed in 

 Paragraph 8-27 and illustrated in Fig. 8-28 or 8-29. The practical problems 

 involved in its construction are those of making proper resolver connections 

 with correct phasing of a-c signals. For the exact transformation, the 

 signals between the six resolvers must pass through isolating amplifiers or 

 phase-shifting devices. The loop-actuating signal, or error signal, is usually 

 an a-c voltage proportional to the difference between the input signal Xa 

 and the controlled antenna position /^a as shown in Fig. 8-34. It is obtained 

 in the exact coordinate transformation from the windings of resolvers, which 

 are mounted on the antenna. In the approximate transformation, the a-c 

 error signal is obtained from the sum of voltages from the vertical gyro roll 



29Note that the calculated maximum phase margin is about 2° greater than the desired 

 design value. This discrepancy, conservative but negligible in an actual system, occurs because 

 the locus was calculated exactly from the transfer function which was determined from 

 approximate equations. 



