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 (c)  
The output pulses from pulse former No. 2 and the output of the prf multivibrator are applied to an AND-circuit. The frequency of the prf multivibrator is controlled by the search/track switch in the logic circuits. When the interrogator is in search mode, the frequency is 146 pps, and when the interrogator is in track mode, the frequency is 21 pps. The pulses from pulse former No. 2, that are coincident with the pulses from prf multivibrator, trigger the countdown multivibrator. The on-time of the prf multivibrator is such that at least one of the pulses from pulse former No. 2 passes through the AND-circuit.

 (d)  
The output of countdown multivibrator and the pulses from pulse former No. 1 are applied to an AND-circuit. The pulses from pulse former No. 1 that fall within the pulses from countdown multivibrator are applied to the modulator as the No. 1 modulation pulse. The No. 1 modulation pulse also triggers the suppression multivibrator. The output of the suppression multivibrator is applied to the air traffic control system, the other DME system and to the suppression amplifier to disable the decoding circuits. The output from pulse former No. 2 is applied to an AND-circuit with the output of the suppressor multivibrator. The pulse from pulse former No. 2, immediately following the No. 1 modulation pulse, is passed by the AND-circuit and used as the No. 2 modulation pulse. The No. 2 modulation pulse is also applied to the computing circuits to provide a time reference.

 (e)  
The modulator applies a high voltage pulse to the plates of the cavity amplifiers in the power amplifier for every modulation pulse input.

 (6)  Distance Computation
 (a)  The sweep multivibrator is triggered by the No. 2 modulation pulse and the output is applied to the linear sweep generator. Linear sweep generator output is compared with a range potentiometer voltage to trigger the selector gate generator when the voltage from the linear sweep generator equals the voltage from the range potentiometer. The time delay between the No. 2 modulation pulse and the comparator output is then analogous to distance, since the potentiometer voltage is determined by the distance. Selector gate generator output and the output of pulse former No. 3 are applied to an AND-circuit. The output of pulse former No. 3 is a positive pulse derived from a phase-shifted sine wave originating in the timing circuits. The amount of phase-shift introduced into the signal from the timing circuits is determined by the position of the resolver.
 EFFECTIVITY
 LH 001-010,031-050,071-081;

 AF 101-120, 123-151;  AZ 201-219;  CONFIG 1 IB 405  01 Page 11
   Apr 25/95

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 (b)  
The output of the AND-circuit triggers the range gate generator and the generator output is applied both to a ramp voltage generator and to an AND-circuit with the decoded distance replies from the decoder. If the distance reply falls within the range gate, a pulse is applied to the error detector along with the output of the ramp voltage generator and to the search/track switch in the logic circuits.

 (c)  
The error detector determines whether the distance reply is in the positive or negative half of the ramp voltage generator output and applies a corresponding positive or negative voltage to the chopper. The output of the chopper, an ac signal whose phase is dependent on the polarity of the signal from the error detector, is applied to the servo drive control in the logic circuits. If the interrogator is in track, the chopper output is applied to the servomotor through the servo-amplifier. The servomotor then drives the resolver, the range potentiometer and the synchro transmitter. The change in position of the resolver produces a time change in the output of pulse former No. 3 which adjusts the range gate to center the distance reply in the range gate (zero the error signal). The synchro transmitter provides the output to the DME indicator for distance display.

 (d)  
If the interrogator is in search, a signal is applied to the servo-amplifier from the servo drive control. The servomotor drives the range potentiometer and the resolver to adjust the selector gate and the pulse former No. 3 output until the distance replies are within the range gate.

 (7)  Logic Circuits
 (a)  
The search/track switch in the logic circuits integrates the gated distance replies from the computing circuits. If the number of replies is sufficiently high, the search/track switch switches the interrogator to the track mode of operation. If the number of replies falls below a minimum level, the search/track switch switches the interrogator to the search mode of operation. The frequency of the prf multivibrator in the interrogation generator is controlled by the search/track switch. If the search/track switch is in search, the frequency is 146 pps. If the search/track switch is in track, the frequency is 21 pps.
　
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