ADF Receiver Flashcards
What is the design of the ADF receiver and its tuning accuracy
Superhet receiver with AM detection tuned in 0.5/1.0 kHz Steps with accuracy better than +-175 Hz
What is the loop RF signal and its initial processing?
It’s voltage from the Goniometer rotor, amplified, phase shift by 90, its phase relative to the sense RF is key.
How does the balanced modulator affect the loop RF signal?
It switches the loop signal at 47~200 Hz alternating it to be in phase or 180 out of phase with the sense RF signal
What occurs when the switched loop RF signal combines with the sense RF signal
In the sense amplifier, they add or subtract during each servo oscillator half-cycle, indicating the station’s position
How is the combined RF signal processed before driving the motor?
It’s amplified, AM detected (using a diode), then the output is sine-wave shaped by a servo amplifier.
What is the role of the two-phase motor in the ADF system?
It rotates the goniometer rotor toward the null position based on the phase difference between its two inputs.
How is the motor’s rotation direction determined?
A 90 phase difference drives rotation; a 180 shift reverses it (ACW for left, CW for right)
When does the two phase motor stops?
When the goniometer rotor reaches the null (right angle to the magnetic field) , causing the loop RF signal to vanish.
How is the goniometer’s position used for bearing indication?
In light aircraft, it drives RBI pointer; in transport aircraft, it couples via a synchro transmitter to an RMI.
What is a relative bearing in this context
Bearing of the station measured clockwise from the aircraft’s nose
How is goniometer angular position transmitted remotely?
Through a synchro system that mechanically couples the goniometer rotor to a transmitter and receiver.
How does the synchro system indicate a change in relative bearing?
An unbalanced synchro induces voltages that drive the bearing indicator pointer pointer to the new position
How does the RMI convert relative bearing to magnetic bearing
Its outer compass card is synchronized with the aircraft’s compass system, updating the magnetic heading.
What happens in the CT rotor and servo system when the aircraft heading changes?
A proportional error voltage is produced, driving the servo motor to rotate the compass card until the error is zero.
What is the role of the balanced modulator in the ADF receiver?
It switches the loop RF signal at 47~200 Hz, alternately making it in phase or 180 out of phase with the sense RF signal.
How does the sense amplifier use the switched loop RF signal?
Adds or subtracts it from the constant sense RF signal during each half cycle, based on the goniometer rotor’s position.
How is the detector output processed before driving the two phase motor?
It is amplified and shaped into a sine wave with a 90 phase shift via servo amplifier.
What determines the direction of rotation of the two phase motor?
2 phase relationship between the servo oscillator and the detector derived sine wave.
How does the system stop the two phase motor?
When goniometer motor reaches the null position (no loop RF signal), the detector output drops to zero, halting the motor.
What is the purpose of coupling the goniometer to a synchro transmitter in transport aircraft?
Remotely display the relative bearing on an RMI via the synchro system.
How is the relative bearing defined in this system?
Measured clockwise from the aircraft’s nose
How is the goniometer search coil adjusted when the aircraft heading changes?
It rotates opposite to the heading change to return to the null position, with its angle transmitted by the synchro system.
How does the synchro system update the bearing indicator?
An unbalanced synchro (due to rotor rotation) induces voltages that rotate the bearing pointer to the new relative bearing.
What happens in the CT rotor of the RMI when the aircraft heading is constant?
No error voltage is generated, so the compass card remains fixed.
How does a change in aircraft heading affect the compass card in the RMI?
Produces error voltage in CT rotor, driving servo motor to rotate compass card until the error is nullified, aligning it with the new magnetic heading.
