2: System Overview
PRC1099A-MS
2-5
2.5.4
Power Amplifier Board
On the Power Amplifier (PA) board, the high-power final RF power
amplifiers that consist of a Class A pre-driver, a push-pull driver stage, and a
push-pull final output stage boost the transmit signal to its final RF output
power or approximately 20W in high power mode or 5W in low power mode.
The PA board uses special broadband transformers for interstage and output
coupling. From the PA board, the SSB channel frequency signal is routed back
to the Audio/Filter board.
2.5.5
Audio/Filter Board Transmit Path 2
On the Audio/Filter board, the 20W transmit signal transmit signal is applied
to one of six separate high-performance, elliptical-function filters that provide
effective attenuation of the harmonic spectrum. The processor selects the filter
based on the selected channel. The signal passes through the ALC detector
and is routed to the Antenna Tuner board.
2.5.6
Automatic Antenna Tuner Transmit Path
The Antenna Tuner board uses detectors at the transmit signal input and
follows a tuning routine, controlled by the processor, to match the radio output
impedance to the antenna for maximum output. To protect the RF power
amplifiers from damage, the output is automatically switched to the 50 ohm
antenna connector when the whip or long-wire antenna is removed.
2.6
DC Power
The PRC1099A operates from a 12 to 15 VDC supply source. The critical
circuitry operates from the regulated 8V and 5V supply lines. The higher
power circuitry operates directly from the 12V supply but continues to operate
down to 10.5V with only minimal reduction in performance specifications.
Table 2-1 Board Functionality
Function
Path
Description
I/O
Audio/Filter Board
VOGAD - U8C
Transmit
Amplifies microphone input and
automatically controls gain.
Input from front-panel handset.
Output to balanced modulator
U6.
Balanced
Modulator - U6
Transmit
Generates DSB 1650 kHz signal,
suppresses carrier.
Input from VOGAD.
Output to J10 to 1650 kHz IF
board.
Product Detector
- U4
Receive
Demodulates 1650 kHz SSB
signal.
Input from 1650 kHz IF board
amplifier.
Output to squelch and audio PA.
BFO input from Synthesizer
board.
