Watkins-Johnson Company WJ-8718-19/FE Instruction Manual page 98

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CIRCUIT DESCRIPTION
Table 3-1. 2nd and 3rd IF Bandwidth Selection
r
BW Filter
BW Switch Select
'on (AM,
FM,
CW Mode)
SSB Modes
Select Pin
50
6.0
3.2
1.0 0.3
USB LSB
A4A1-15 (Wl)
+5
0
0 0
0
+5
A4A1-17
(6 kHz)
0
+5
0
0 0
0
A4A1-19
(3.2 kHz)
0
0
+5
+ 5
+ 5
0
A4A3-15 (W2)
+5
+5 +5
0
0
0
A4A3-17
(1.0 kHz)
0 0
0
+ 5
0
0
A4A3-19 (0.3 kHz)
0
0 0
0
+5 0
Table 3-2. Detection Mode Selection.
i
1
Mode
Detection Mode Switch Selection
1
Select Pin
AM
FM
CW
USB
LSB DF
^
A4A10-47
(AM SEL)
+5 0
0
0
0
1
A4A9-41
(FM)
0
+5 0
0 0
A4A9-43
(CW/SSB)
0
0
+5
+5+
5
A5A3-43
(OFFSET EN)0
0
+5
0 0
j
1
A5A3-57
(BFO INH)
+5 +5
0
0 0
3.3.4.2 10.7 MHz/455 kHz Converter (A4A2) (794254)
The amplified 2nd IF output from A4A1-57 drives the 50 ohm input of the
10.7 MHz/455 kHz Converter, or the 3rd Mixer A4A2-57. The 3rd Mixer also receives
the LO signal from the 3rd LO Synthesizer, A5A1, which is fixed at a frequency of
11.155 MHz. In DF mode, the internal bandwidth of A4A2 is set at 2.2 kHz by a
bandpass filter. The 3rd LO and 2nd IF are mixed by the 3rd Mixer to produce a 3rd
IF of 455 kHz. The 3rd IF output, A4A2-19, of the 3rd Mixer is stepped up to an
impedance of 1000 ohms and drives the input of the 455 kHz Filter Switch, A4A3.
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