Watkins-Johnson Company WJ-8718A/MFP Instruction Supplement page 96

WJ-8718A/MFP
Table 3-18. Input Select Address Codes
Selected
Address Line
Analog Channel C B A
INO 0 0 0
IN1 0 0 1
IN2
0
1 0
IN3 0 1 1
IN4
1
0 0
INS 1
0
1
IN6 1 1 0
IN7 1 1 1
TABLE 3-18
TABLE 3-19
All analog inputs are referenced to Vcc (+5 V). The binary output is derived by the
equation:
VIN
binary output
=
VREF x 256
Table
3-19
lists the analog inputs and their functions.
Table 3-19. U25 Analog Inputs and Functions
Input Function
INO
BFO Tuning Voltage
IN1 Not Used
IN2 Signal Strength
IN3 Combined Audio
IN4
1st LO Tuning Voltage
INS -15 V supply
IN6 +15 V supply
IN7 2nd LO Tuning Voltage
Clock circuit U18B and U18C provide timing and control of the AID conversion
rate. Circuit U18H is configured as an RC oscillator that provides an approximately 700 kHz
clock that is conditioned by U18C before entering the
AID
clock input.
3.2.5.12 Analog Inputs
INO is the input for the BFO tuning voltage. This voltage is tested to determine if
the BFO synthesizer is locked. If unlocked, an error condition will occur in testing.
IN2, the signal strength input, is taken from the AGC circuit, invert.ed and
amplified by U24A. Potentiometer R7 sets the multiplication ratio along with R8. Refer to
paragraph 4.1.2.2· for R 7 adjustment procedures. MAN signal strength is also passed through
isolation amplifier U24B to protect the meter circuit from interfering with the AGC signal
strength circui
1.
3-41