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WJ-8718A & WJ-8718A/MFP 1-Hz OPTION
PRINCIPLES OF OPERATION AND CIRCUIT DESCRIPTION
In stock receivers (10-Hz tuning resolution) the coaxial cable bridge named W6 and placed on
the bottom side of the receiver - towards the rear of the unit and in correspondence of the A6
I/O mainboard - leads the 11.155,000 MHz signal coming from the third L.O. to the third
mixer (U1 on the A4A2 card) in order it is mixed with the 10.7 MHz 2nd IF signal and
produces a 3rd IF of 455 kHz. The 3rd L.O. output signal is applied to J9 (P8 on W6) and the
3rd mixer input corresponds to J7 (P10 on W6).
Installing the 1-Hz Option implies that the coaxial bridge W6 is removed and that the 3rd
L.O. signal is applied to pin 3 of the X9 socket that corresponds to the new 796022 1-Hz
Option card instead (1Hz-W2 cable starting at P4/J9). Then a signal coming from pin 5 of the
same X9 socket (1-Hz card) is applied to the 3rd mixer input (1Hz-W1 cable coming to
P1/J7).
So it is evident that the 796022 1-Hz Option card produces 1-Hz shifts (from -9 Hz to + 9 Hz)
in the 11.155 MHz signal that comes to the 3rd mixer, so that the tuning resolution becomes 1
Hz. Obviously the 1-Hz shifts depend from the tuning encoder (and from the numeric
keyboard in the /MFP receivers) and are also sensed by the tuning display.
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