| The most important
board in the entire radio is the Pass-Band Tuning Board.
This board is considered the "heart-beat" of the radio
because it generates several fixed frequencies and reference
signal needed to operate the radio. Those
signals are indicated with the black arrow lines
going from the Pass-Band Tuning Board. This
board generates the 40.0Mhz master oscillator frequency
from which the entire operations of the radio depend on.
From that master oscillator frequency this board derives several other fixed frequencies
which are supplied to several other boards.
The receive function signal flow is
shown with the blue arrow lines. Starting at the antenna the receive signal flows through a
high pass and low pass filter to limit the broad range of
incoming frequencies to a narrower tuning range set by the
band switch. The signal then travels to the
UP-Converter board where its mixed with the VCO frequency to
produce the 1st IF frequency. From there it travels
to the 2nd Mixer Board where the signal is mixed with the
injection signal from the Pass Band Tuning Board to produce
the 2nd IF signal at 5.645Mhz. From there the
signal is
sent to the IF Switch Board where in the receive mode is
sent to the IF Filter board. The
Filter Board limits the bandwidth of the receive signal with
selectable filters according to the selected mode of
operation. The output of the Filter Board
goes the IF/Audio Board where the signal is AGC controlled,
demodulated with the audio then amplified to drive the
speaker.
The transmit function signal flow
is shown with the red arrow
lines. Starting at the
microphone or key, these devices are attached to the
Transmit Exciter Board. This board takes
the audio from the microphone amplifies it and mixes that with
the BFO frequency to create the 1st transmit IF frequency.
This board also controls the VOX functions of the
transceiver. Next the signal goes to the IF Switch
Board where in the transmit mode that board switches it to
the Filter Board where the signal only passes through the
SSB filter to limit the signal bandwidth of the signal to
2.3Khz. From there the signal passes to the
IF/Audio board which contains a variable attenuator used to
control the output power level of the transmitter.
The transmit signal then is sent through the 2nd Mixer board
and the UP-converter Board to produce the operating transmit
frequency. Through each of these boards the
input signal is mixed with a fixed frequency to create the
operating frequency at the output of the Up-Converter board.
From there the low level transmit signal goes through the
high pass filter board to eliminate all harmonics of the
actual frequency. The filtered signal then goes to the
power amplifier where up to 150 watts of RF power output can be
created depending on the drive level set by the variable
attenuator. The high power signal then
goes through the low pass filter to further eliminate all
harmonic frequencies generated by the power amplifier to
produce a clean signal which is sent to the antenna
connector.
The frequency synthesizer function
produces the correct injection signal frequency to the
Up-Converter Board, refer to the
violet arrow lines for
signal flow. This injection signal is mixed with the
incoming signal to the Up-Converter to produce a correctly
tuned output frequency. In the receive
mode this frequency would be the 1st IF signal going to the
2nd Mixed Board, and in the transmit mode the output is the
actual transmit frequency which goes to the High-Pass Filter
Board and PA Amplifier. The Synthesizer
has three major interdependent boards. The VCO
Board produces the actual injection frequency from the data
supplied from the other boards. The
Translator Board takes signal inputs from the PTO, Pass-Band
Tuning Board, and VCO Board, mixed those signals together,
then divides that signal in frequency to produce an varying
output reference signal proportionate to the VCO frequency.
That varying reference signal is sent back to the VCO Board
to the phase detector circuit. The Phase Detector
compares that varying reference signal to the 500Khz
reference signal from the Pass-Band Tuning Board.
When the Phase Detector determines both frequencies exactly
match the detector locks the VCO frequency. When
the VCO frequency is locked, that VCO frequency is set to
the correct injection frequency to operate the transceiver.
In this process of producing a locked frequency the Digital
Board determines the actual VCO frequency tuning range from
data supplied from the band switch. The
Digital Display Board determines the actual operating
frequency and displays that frequency at the front panel.
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