Southern Avionics Company SD100 Manual Do Utilizador
SD SERIES TRANSMITTER
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Southern Avionics Company
2.2 SLF31002/00 - Basic Dual Transmitter
2.2.1 P.A. PCB
SLP10001 RF Power Amplifier
The RF Power Amplifier PCB is a Pulse Width Modulator and RF power amplifier in one package. The Pulse width
Modulator section is commonly called the Modulator and the RF Power Amplifier is commonly called the PA.
These terms will be used for the rest of this discussion.
Modulator section is commonly called the Modulator and the RF Power Amplifier is commonly called the PA.
These terms will be used for the rest of this discussion.
The PA section is comprised of a broadband pre-amplifier and Class "D" RF power amplifier. It inputs
either the Controller / Monitor controlled Direct Digital Synthesized RF drive signal or a customer furnished signal.
Its output power is controlled by the Modulator.
Its output power is controlled by the Modulator.
The Modulator is basically a 75 kHz buck converter. It inputs D.C. High Voltage from the PA Power supply
Section and uses a 75 kHz square-wave input from the Controller / Monitor-I/O section to chop, filter and reduce the
DC-HV to a level usable by the PA. The Voltage the Modulator outputs to the PA is a function of both the input HV
and the duty cycle of the 75 Khz square-wave. The 75 kHz Duty cycle of is set to 45% and not used to change the
overall RF Power output level. The power output level of the PA is set by changing the input DC-HV and this is done
under Controller / Monitor control. To Modulate the PA, audio frequency information in the form of a Morse Code
Station ID tone sequence or an AWOS voice announcement, pulse width modulates the 75 kHz signal controlling the
Modulator section thus varying its output voltage at the audio rate. This varies the instantaneous voltage applied to
the PA, modulating its output Power.
DC-HV to a level usable by the PA. The Voltage the Modulator outputs to the PA is a function of both the input HV
and the duty cycle of the 75 Khz square-wave. The 75 kHz Duty cycle of is set to 45% and not used to change the
overall RF Power output level. The power output level of the PA is set by changing the input DC-HV and this is done
under Controller / Monitor control. To Modulate the PA, audio frequency information in the form of a Morse Code
Station ID tone sequence or an AWOS voice announcement, pulse width modulates the 75 kHz signal controlling the
Modulator section thus varying its output voltage at the audio rate. This varies the instantaneous voltage applied to
the PA, modulating its output Power.
Critical parameters such as PA Voltage , Current , and Temperature are sensed and monitored continuously
by the Controller / Monitor. Local (on board automatic) over-current protection is built in. The protection scheme
also provides interrupt driven fault reporting to the Controller / Monitor.
also provides interrupt driven fault reporting to the Controller / Monitor.