Theory Of Operation, Radiobeacon; Functional Description: Ss-800Avs - SAC SS-800AVS Manual

2 THEORY OF OPERATION, RADIOBEACON
2.1 Functional Description: SS-800AVS
The transmitter signal is generated at low level by amplitude
modulating the output of the synthesized carrier oscillator with
an audio signal. The audio signal is derived from the summing of
a voice type line input signal with a keyed tone code signal.
The audio signal to the modulator is controlled by squelch and
automatic-gain-controlled circuitry. Audio line inputs greater
than the squelch threshold level are permitted to pass through to
the modulator. Amplitude of the line input signals is maintained
by the AGC circuit.
The code signal is generated by the Keyer and the Recycle PWB. The
1020 Hz or 400 Hz output of a code tone oscillator is gated on and
off by a logic signal from the Keyer. A second gating circuit
operated by the squelch detector permits high amplitude code mod-
ulation during voice signal absence and low amplitude code modulation
during voice signal presence.
The modulated RF signal is filtered and then fed to a linear amplifier
consisting of a Class A preamplifier, a push-pull class AB driver
stage, and a parallel push-pull class AB final amplifier.
The signal then goes to the antenna system which consists of the
antenna coupler and the antenna.
The power supply is a conventional full wave supply capable of
delivering 8 amps at 50 volts. The transmitter uses up to 6 amps
at full power thus leaving an ample supply for battery charging.
The optional battery system maintains the batteries in a charged
state and automatically switches the transmitter to battery power
whenever AC power is lost.
Output current is sensed at the final stage to provide an automatic
shutdown capability. A current and voltage limiter protects the
final circuit from line surges or voltage and current surges in the
final.
DC current in one of the finaltransistors, and RF output power are
metered. A DC voltmeter with probe is also built in. A tuning
indication is derived from a reflected power measurement in the
antenna coupler.
SS-800AVS
Southern Avionics
ii
Company