(f)
The output of the pulse-shaping multivibrator, is a pulse approximately 1 usec wide. The output pulse is applied to a 9.8-usec delay line and through a differentiator and an OR-circuit to a coincidence circuit. The delayed pulse from the 9.8-usec delay line is applied to an 18-usec delay line and a comparator. The comparators square the outputs of the delay lines. The resulting pulse width is 4 usec. Comparator output are applied to the time-delay selector.
(g)
The time-delay selector applies either the 9.8-usec delayed pulse or the 27.8-usec delayed pulse to the coincidence circuit. The 9.8-usec delay is selected if the interrogator is tuned to an X channel, and the 27.8-usec delay is selected if the interrogator is tuned to a Y channel.
(h)
The coincidence circuit compares the delayed output with the nondelayed output from the pulse-shaping multivibrator or the deblocker amplifier. If the received pulses are properly spaced, 12 usec on X channels, 30 usec on Y channels, the second pulse of the nondelayed pulse pair will be applied to the coincidence circuit at the same time the first pulse of the delayed pulse pair is applied to the coincidence circuit. If the pulses are time coincident, the coincidence circuit then has an output to trigger the reply multivibrator.
EFFECTIVITY
LH 001-010,031-050,071-081;
AF 101-120, 123-151; AZ 201-219; CONFIG 1 IB 405 01 Page 6
Apr 25/95
34-55-00
VHF NAV CONTROL DME NO. 1 INTERROGATOR PANEL
DME NO. 1 System - Functional Block Diagram
Figure 3 (Sheet 1)
EFFECTIVITY CONFIG 1
LH 001-010,031-050,071-081; 799 Page 7
AF 101-120,123-151; AZ 201-219;
34-55-00
Apr 25/95IB 405
DME No. 1 System - Functional Block Diagram
Figure 3 (Sheet 2)
EFFECTIVITY CONFIG 1
LH 001-010,031-050,071-081; 799 Page 8
AF 101-120,123-151; AZ 201-219;
34-55-00
Apr 25/95IB 405
DME NO. 1 ANTENNA
DME No. 1 System - Functional Block Diagram
Figure 3 (Sheet 3)
EFFECTIVITY CONFIG 1
LH 001-010,031-050,071-081; 799 Page 9
AF 101-120,123-151; AZ 201-219;
34-55-00
Apr 25/95IB 405
(i)
If the amplitude of the reply signals are instantaneously high, the agc circuits may not have time to react. This might happen if the interrogator is channeled to a nearby station. If the receiver is in saturation and the leading edge of the second pulse of a pulse pair is not well enough defined, the first comparator will produce an output from the first pulse onlt. The multivibrator will then be triggered by only the first pulse of the pair, and a second nondelayed pulse from the multivibrator will not be present in the coincidence circuit to premit decoding. In this case, a second nondelayed pulse is applied from the signal detector to the coincidence circuit through the deblocker amplifier and differentiator to permit decoding and allow the agc to build up to the point where the decoder operates in the normal manner.
(j)
The output of the reply multivibrator is applied to an AND-circuit, to the identification ringing circuit, and to the computing circuits. The AND-circuit receives pulses from the video amplifier in the receiver circuits along with the pulses from the reply multivibrator. The pulses from the video amplifier contain pulse amplitude information necessary for the operation of the agc circuit. The AND-circuit allows the video amplifier output pulses to pass if they are time coincident with the decoded pulses from the reply multivibrator. This blocks noise and pulses not properly coded from being applied to the agc circuit.
(k)
The agc circuit integrates the pulses and generates a voltage to control the gain of the first IF amplifier. The identification ringing circuit detects the presence of a 1350-Hz tone and applies the tone through an amplifier to the flight interphone system.
(5) Interrogation Pulse Generation
(a)
The timing circuits consist of a 4045.6-Hz oscillator. The output of the timing oscillator is applied to the interrogation generator which encodes the interrogation pulses and to the computing circuits as a distance-measuring time base
(b)
The signal from the timing circuits is applied to pulse formers No. 1 and No. 2 through a 12-usec phase lag circuit and a 24-usec phase lead circuit. When the interrogator is tuned to a X channel, the 24-usec lead circuit is inactivated and provides zero phase shift. The phase difference between the signals applied to the pulse formers is then 12-usec on X channels and 36-usec on Y channels.
EFFECTIVITY
LH 001-010,031-050,071-081;
AF 101-120, 123-151; AZ 201-219; CONFIG 1 IB 405 01 Page 10 中國航空網 m.k6050.com 航空翻譯 www.aviation.cn 本文鏈接地址：747飛機維護手冊AMM CHAPTER 34 - NAVIGATION 第34章導航4(86)
