Watkins-Johnson Company WJ-8718-19/FE Instruction Manual page 89

CIRCUIT DESCRIPTION [A7T 0„,0 ,
WJ-8718-19/FE HF RECEIVER
3-6
e. Mode Select - The Digital Control sends a 5-bit data word to
select AM, FM or CW/SSB modes.
f. Gain Select - The Digital Control Section sends a 2-bit data
word to select SLOW, FST or MAN gain modes. In MAN mode
the Digital Control Section also sends a MAN GAIN analog
control voltage to vary the gain of the 3rd IF amplifier.
g. IF Out - A high level, 3rd IF signal is provided as a rear panel
receiver output at J12. This output is 50 ohms, bandwidth
limited by the 3rd IF filter, and is nominally 67 dB above the
2nd IF input signal.
h. Line Audio Out - A demodulated AM, FM or CW/SSB audio
signal is provided as a rear panel receiver output at J15/16.
This output is 26 Vac into 600 ohms (+30 dBm).
i. RF Gain Control - This dc voltage is supplied to the RF/IF
Conversion Section. This level is nominally 0 Vdc under
normal signal conditions, increasing to -4 Vdc under maximum-
signal conditions.
j. Status - Two dc outputs are send to the Digital Control
Section and represent the relative signal strength and line
audio output level.
k. Combined Audio - This low level audio is sent to the Digital
Control for distribution to the front panel headphone amplifier.
3.2.5 SYNTHESIZER SECTION
A general discussion of the Synthesizer Section functions and signal
interfaces is provided in the following paragraphs.
3.2.5.1 Synthesizer Section Functions
The Synthesizer Section performs the following functions:
a. LO Signal Generation - The Synthesizer Section translates
digital tuning data from the Digital Control Section into the
1st, 2nd, 3rd and BFO signals required for operation of the
mixers in the RF/IF Conversion and IF/Demodulator Sections.
b. External Reference Locking - Internal phase locked loops the
accuracy of the four LO signals to an external frequency
reference source for high tuning accuracy.