(c)
 Tune A sequence The purpose of tune A is to adjust the antenna circuits so that HF signal current and voltage are in phase. To this end, after detection, a discriminator delivers an error signal proportional to the phase difference during 50 ms. The polarity of this signal determines the elements required to achieve tuning. Two cases may arise:

 (d)
 Tune B sequence The purpose of tune B is to match the antenna load with the transmitter output circuits. To this end, a load discriminator compares the HF current and voltage.

 1_ Positive error signal
 The antenna circuit impedance is inductive and is below the
 parallel resonance. The error signal is brought to zero by
 acting on capacitor C3.
 2_ Negative or null error voltage
 Two cases may arise:
 - the antenna circuit impedance is above the parallel
 resonance (high band):
 The error signal is brought to a positive value through
 variation of inductance L2 and brought to a null value by
 capacitor C3.
 - the antenna circuit impedance is below the parallel
 resonance (low band):
 The error signal is brought to a positive value through
 variation of capacitor C2 and then to a null value by
 capacitor C3.
 When the phase error signal is brought to a null value, the
 sequence counter controls change to the next sequence: tune B.

R 1EFF : 051-099, 106-149, 201-299, 301-399, 1 23-11-00Page 50 1401-499, 1Aug 01/05 1 1 1CES 1

 This comparison gives an error voltage proportional to the
 difference between the HF circuit impedance and an impedance of
 50 ohms.
 Two cases may arise:

 1_ Load lower than 50 ohms (negative). It is not necessary to
 modify the tuning circuits: the sequence counter circuit
 controls change to the next sequence, i.e. tune C.
 2_ Load equal or greater than 50 ohms (positive)
 Two cases may arise:
 - inductor L2 is used in the tune A sequence. This inductance
 is re-used to decrease the reflected power below a preset
 level
 - inductor L2 is not re-used to achieve tune A sequence.
 It is brought to its maximum inductance. As this tuning
 modifies phase tuning, capacitor C3 must be re-adjusted.
 When the phase error voltage is null:
 . if the load error voltage is negative the next sequence
 starts,
 . otherwise inductor L2 is adjusted to decrease reflected
 power to a preset level.
 When reflected power is decreased, the sequence counter
 starts the next sequence i.e. tune C.

 (e) Tune C sequence The purpose of the tune C is to complete previous adjustments and obtain a VSWR (voltage standing-wave ratio) lower than 1.3. In this sequence, capacitor C3 is adjusted to maintain voltage-current phase shift to zero. Capacitor C2 and/or inductor L2 are tuned to bring reflected power below a preset level. If inductor L2 has not been used in tune A and B:
 -capacitor C2 is adjusted until the reflected power value decreases below a preset level corresponding to a VSWR lower than 1.3
 If inductor L2 has been used in tune A or B:
 -inductor L2 is adjusted again so that VSWR goes below a preset
 level. If adjustment is impossible and if inductor L2 is at maximum inductance:
 -capacitor C2 is tuned again until VSWR is lower than 1.3. When a VSWR lower than 1.3 is obtained, the sequence counter controls start of the next sequence i.e. operational position.
R 1EFF : 051-099, 106-149, 201-299, 301-399, 1 23-11-00Page 51 1401-499, 1Aug 01/05 1 1 1CES 1

 (f) Operational position In this sequence, the tuning control line is disconnected from ground. The antenna coupler can operate. If a new frequency is selected:
 -the antenna coupler goes back to the start sequence and the tuning cycle starts again.
 (3) Fault indications Fault information of the coupler can be transmitted by discretes to the HF transceiver. In this case, the HF transceiver will take these items of information into account and will transmit them to the CFDIU.
 **ON A/C ALL
 7. Operation
_________
 **ON A/C 001-049, 101-105, 151-199,
 A. Receive Function The HF audio modulated signals transmitted by the stations are picked-up by the antenna and transmitted to the antenna coupler. The coupler adapts the impedance between the antenna and the HF transceiver. The signal from the HF coupler is transmitted to the HF transceiver by a coaxial cable. The HF transceiver, tuned on the selected frequency by one of the RMP, demodulates HF signals into AF signals. The AF signals are transmitted via the AMU, to the audio equipment or SELCAL system.
　
中國航空網 m.k6050.com
航空翻譯 www.aviation.cn
本文鏈接地址：A320飛機維護手冊 AMM Communications 通訊1(48)