(8)
The loop error signal is phase-shifted 90 degrees before entering the balanced modulator, so alternate blocks are in phase with or out of phase with the sense signal and consequently either increase or decrease its amplitude. The resultant signal is the tuned rf sense signal with a 220-Hz modulation envelope. The depth of modulation depends on the magnitude of the loop error signal and falls to zero when the goniometer search coil is orientated for zero coupling with the magnetic component of the received signal. The phase of the output from the search coil reverses as it passes through either of the two positions of zero coupling (null positions). The signal passes through the three-stage frequency converter and the IF modulating frequency is recovered. The recovered 220 Hz is amplified in the variable-phase gonio amplifier and provides the input to the control-phase windings of the two- phase gonio servomotor. The amplitude of this input falls to zero when the gonio search coil is at either null position. The phase of the input reverses either side of both null positions, so one null is an unstable position and the servomotor drives the search coil to the other null position, where it stops.
(9)
When system operation is switched to the LOOP mode, relays K1 and K2 (Sheet 1, Fig. 3) are energized. The sense antenna is disconnected by relay K1 and a dummy sense antenna is substituted. The phase splitter is switched to operate as an extra stage of loop error signal amplification. Relay K2 disconnects the fixed-phase switching signal from the balanced modulator and substitutes a fixed bias voltage that opens one diode for the passage of the loop error signal. Relay K2 also disconnects the goniometer servomotor control phase windings from the variphase amplifier and reconnects them to a new supply obtained from the LOOP manual control circuit in the control panel. The new supply is derived by the LOOP manual control from the fixed-phase amplifier. The phase of the supply is advanced or retarded by 90 degrees according to the direction in which the control is turned. The amplitude of the supply is varied according to the degree of rotation. The LOOP manual control can therefore be used to control the direction and speed of rotation of the goniometer servomotor.
EFFECTIVITY
AF 101-156; IB 405; CONFIG 1 LH 001-003; SN 301-302 03 Page 7 Apr 25/86
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ADF CONTROL PANEL
ADF System Functional Block Diagram
Figure 3 (Sheet 1)
EFFECTIVITY AF 101-151; LH 001-010;
CONFIG 1 SN ALL; IB 405
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TO FLT INPH SYSTEM
ADF System Functional Block Diagram
Figure 3 (Sheet 2)
EFFECTIVITYAF 101-151; LH 001-010;
CONFIG 1 SN ALL; IB 405
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(10)
When system operation is switched to the ANT mode, relays K1 and K2 are de-energized so the sense antenna is reconnected, and the power supplies to the loop error signal amplifier, the variphase amplifier the 220-Hz oscillator and the fixed-phase amplifier are switched off. Therefore, the receiver operates as a normal communications receiver and the LOOP manual control at the controller is inoperative.
(11)
The tuning system in the receiver employs varactor capacitor tuned stages in the rf and IF tuned circuits. Precise voltages for the varactor tuning are produced in the control panel from -100 and -25 volt supplies which are derived from the receiver. As each operating frequency is selected at the control panel, the magnitude of the voltage from the control panel to the receiver is set to the required value to give the correct tuning capacitance from the varactors.
(12)
Diodes are used in the receiver to select the particular crystals required in the oscillator stages, and also to select the tuning coils for the rf stages. Appropriate connections are made to control lines connected to the control panel, again by means of the frequency selector switches, to select the diodes required for each crystal and coil. Diode selection is also used to activate the BFO circuits in the receiver. A potentiometer in the control panel provides BFO note control.
(13)
Rf and IF (audio) gain is controlled through fixed resistors and a potentiometer. In the ADF mode, rf gain is preset and audio gain is variable. In the ANT and LOOP modes, audio gain is preset and rf gain is variable.
(14)
Control Panel Operation
(a) Receiver operation is controlled by a four-position function switch. In the OFF position, power is disconnected from the receiver. In the ADF position, the receiver is switched on and set up for automatic direction finding with simultaneous audio reception. In the ANT position the receiver operates from the sense antenna alone as a sensitive communications receiver. In the LOOP position the receiver operates from the loop antenna alone and may then be used either for manually controlled direction finding or for communications reception in regions of severe static where manual control of the loop attitude can sometimes improve the signal to noise ratio.
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