Watkins-Johnson Company WJ-8718-19/FE Instruction Manual page 100

WJ-8718-19/FE HF RECEIVER
CIRCUIT DESCRIPTION
3.3.4.7
Audio Amplifier (A4A10) (7459)
The AM Audio output from A4A7-5L drives the input to the Audio
Amplifier, A4A10-51, and the FM/CW/SSB Audio output from A4A9-57 drives the input
to the Audio Amplifier, A4A10-57. In AM mode, selected by +5 Vdc at pin 47 (see
Table 3-2 for a summary of detection mode selection), the AM Audio at pin 51 is gated
through a summing amplifier at unity gain and appears at pin 55. In FM, CW or SSB
Modes, pin 47 is 0 Vdc, and the FM/CW/SSB Audio at pin 57 is gated through the
summing amplifier and appears at pin 55. Combined Audio at pin 55 is routed through
the front panel Audio Level control to the high level Line Audio Amplifier via pin 17.
The Line Audio amplifier amplifies the signal and outputs it through A4A10-13 to rear
panel J16. A rectifier samples the output of the Line Audio amplifier and supplies the
front panel meter in the LINE AUDIO setting. A low level audio signal from the from
the front panel headphone amplifier drives the Auxiliary Phone amplifier. The
Auxiliary Phone out signal at A4A10-19 appears at the rear panel J16.
3.3.5 SYNTHESIZER SECTION
Figure 3-6 is a block diagram of the Synthesizer Section. The
Synthesizer Section is mounted on the Synthesizer Motherboard P. W. Assembly A4. As
shown in Figure 3-6, the Synthesizer Section consists of three major modules: 1st and
3rd LO/Time Base, A5A1; 2nd LO Synthesizer, A5A2; BFO Synthesizer, A5A3.
1ST LO OUT
1ST LO
SYNTHESIZER
P/0 A5A1
2ND LO OUT
2ND LO
SYNTHESIZER
A5A2
40 kHz
1 1 •
MHz
10
kHz
1STLO
TUNING DATA
/
/
2NDLO
TUNING DATA
3RD LO OUT
3RD LO
SYNTHESIZER
P/O A5A1
50
kHz
10 kHz
BFO OUT
BFO
SYNTHESIZER
A5A3
I
1 kHz
/
/
BFO TUNING DATA
Figure 3-6. Synthesizer Section Block Diagram
1 MHz REF IN
TIME BASE
P/O A5A1
REF OUTPUTS
3-17