"A PA" is "A" set (HF) and "PA" is power amplifier. This control is used to tune the PA output circuit and receiver rf amplifier to resonance with the variometer. To get the most transmit signal radiated the aerial should resonant at the frequency in use. By adjusting both controls this is achieved. Being adjustable allows for change in aerial length and frequency. The same principle applies to the receiver circuit. At resonance the maximum received signal is applied to the receiver rf amplifier resulting in a stronger signal in the headphones.
It's calibrated in frequency to allow some pre-tuning. The variometer is also calibrated and this is used in conjunction with the flick mechanism to speed band change.
The meter switch in the AE position indicates rf power through the variometer. The maximum the better.
The AVC position shows receiver is properly tuned when at maximum dip.
Read the manual section on netting drill in harbour and practice.
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