General Principles Of Operation - Motorola HF-SSB MICOM-500E-A G761AA Owner's Manual

General principles of operation

Block diagram of the power amplifier is shown at Fig.4. Input RF signal with 25W nominal
l e v e l c o m e s t h r o u g h " R F I n " c o n n e c t o r t o T S 1 2 2 7 b o a r d o f P A MP 5 0 0 a m p l i f y i n g d e v i c e
consisting of 4-channel power splitter and 4-channel amplifier. The power splitter unit contents:
Input signal level sensor;
Input relay Rx/Tx that provides the possibility to operate in BYPASS mode;
Input signal attenuator used by the amplifier protection system;
Signal frequency sensor;
Power splitter.
The signal comes from power splitter output to four 150W amplifying sections inputs.
Then, amplified signal is summed by power Combiner (TS5 226).
The signal then comes from Combiner output to harmonic filter (TS5 223) input and then
t o o u t p u t l e v e l s e n s o r , o u t p u t r e l a y R x / T x a n d t o o u t p u t c o n n e c t o r " R F O U T " .
The controller provides the power amplifier control, status monitoring and its protection in
emergency situations. By analyzing the input signal level, the controller provides protection of the
amplifier input against overloading. By measuring the input signal frequency the controller selects
and switches on appropriate harmonic filter. Control system also provides the control of the
amplifier sink temperature. Depending of its level the forced air cooling system shall be switched on
or output power level shall be reduced if necessary and if the temperature limit is exceeded the
amplifier shall be switched to BYPASS mode. By analyzing signals from output sensor the
controller monitors the status of load, and if VSWR in the load is higher than maximum allowed one
the controller decreases output power, and if VSWR is higher than 4 the controller switches the
amplifier to BYPASS mode. Besides, the controller sends to CONTROL output connector the
signals that proportional to forward and reflected power at the amplifier output and that assigned for
output power control from an external device, for example, exciter.
Thus, the amplifier control system provides full its status and operability control. It
switches the amplifier to BYPASS mode in the following cases:
VSWR > 1:4
Input signal frequency is out of operation band
The temperature mode is out of limits
In other cases, as well as in switched off mode when normal operation of the
amplifier is impossible. In that case the possibility of normal operation of external
transceiver is provided.
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HF-SSB Micom – 500E-A