Watkins-Johnson Company WJ-8718-19/FE Instruction Manual page 101

CIRCUIT DESCRIPTION WJ-8718-19/FE HF RECEIVER
3.3.5.1 1st L.O. Synthesizer (A5A1) (791630)
™cn c The 1St L0 receives BCD tuned frequency command data from the four
MSDs of the receiver tuned frequency readout. The BCD numbers range in value of
0000 to 2999 corresponding to receiver tuned frequencies of 00.00XXX MHz to
29.99XXX MHz. The output of the 1st LO tunes from 42.91 MHz to 72.90 MHz in
10 kHz steps in accordance with the BCD tuned frequency data. A stable 40 kHz time
base signal provides a precise reference for the 1st LO phase lock loop control
circuits. K
3-3.5.2 2nd L.O. Synthesizer (A5A2) (791601)
..., , uThe 2nd L0 receives BCD tuned frequency command data from the three
LbD s ol the receiver tuned frequency readout. The BCD numbers range in value from
000 to 999 corresponding to receiver tuned frequencies of XX.XX000 MHz to
XX.XX999 MHz. The output of the 2nd LO tunes down from 32.21000 MHz to
32.20001 MHz as the BCD data increments from 000 to 999. Stable 10 kHz and 1 MHz
time base signals provide precise references for the 2nd LO phase lock loop control
circuits.
3-3.5.3 3rd L.O. Synthesizer (P/O A5A1) (791629)
r T h e 3rd LO Synthesizer produces a fixed frequency output of 11.155 MHz
Basic frequency control is obtained by an 11.155 MHz crystal oscillator. The exact
frequency of oscillation is precisely locked to 10 kHz and 50 kHz time base reference
signals by a phase locked loop.
3.3.5.5 BFO Synthesizer (A5A3) (791576)
The BFO Synthesizer receives BCD offset frequency command data from the
MSD and LSD of the BFO offset switch, A9. The BCD numbers range in value from 00
to 89 corresponding to offset frequencies of 0.0 kHz to 8.9 kHz. Offset control data
from the "+, o, -" switch section of A9 programs the direction of BFO offset. The
output of the BFO tunes from 446.1 kHz (455 kHz - 8.9 kHz) to 463.9 kHz
(455 kHz + 8.9 kHz). In the AM and FM modes, BFO INH, A4A8-57, is high, shutting
off the BFO output at A5-P15, even though the BFO itself is oscillating. In SSB
modes, OFFSET ENABLE, A4A8-43 is low, fixing the BFO output at 455.000 kHz. A
stable 1 kHz time base signal provides a precise reference for the BFO phase lock loop
control circuits.
3.3.5.6 Time Base (P/O A5A1) (791600)
All four synthesizer circuits are synchronized by a common Time Base
Reference frequencies of 1 MHz, 50 kHz, 40 kHz, 10 kHz, and 1 kHz are supplied from
a 2 MHz temperature compensated crystal oscillator or from a 1 MHz external source
input at rear panel jack Jll. The rear panel INT/EXT clock switch S2 allows selection
at the internal and external reference. When in the internal mode, the 1 MHz internal
•eference is output from rear panel jack Jll.
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