55
Notch Filter Alignment
This procedure aligns the six notch filters. The procedure describes
alignment of a single filter, the procedure is identical for all six filters.
This alignment should be done only if the notch filter check in the
PERFORMANCE TESTS section of the manual has failed.
1) Set the function generator for 200 mV pk-pk sine wave.
2) In CAL MENU 1 (press BSP and TIME keys simultaneously) set the
FS700's attenuators for 64 dB. Look at the LORAN OUTPUT on
the scope. Set the notch filters to the middle of their range.
Remove jumper JP104 and attach the function generator to the right
pin of the jumper (viewed from the front). Install jumpers JP105,
JP106, and JP107 (these are out in normal operation). This
configuration bypasses the FS700's 100 kHz bandpass filter.
3) Set one filter to its lowest frequency (40 or 110 kHz). Set the
function generator to the same frequency.
4) Adjust the two filter inductors (L107 and L108, for example) to
minimize the signal output.
5) Set the function generator to the maximum filter frequency (90 or
220 kHz). Tune the filter to minimize its output.
6) Adjust the trim capacitors (C119C-F, for example) to minimize the
signal output.
7) Set the filter to its midrange.
8) Repeat this procedure for the rest of the filters.
9) Set the filters to their extremes (40 and 220 kHz).
10) Install jumper JP104 and remove JP105, JP106, and JP107.
