
Model 8640B
TM 9-4935-601-14-7&P
ADJUSTMENTS
5-37. RF FILTER ADJUSTMENT (Cont'd)
4
. For each of the frequency range bands listed in Table 5-3, perform the following:
a. Connect spectrum analyzer's RF input to tracking generator's RF output (use test cables and adapter as shown in
test setup). Set Signal Generator's RANGE and FREQUENCY TUNE controls as listed in the table. Set
spectrum analyzer's frequency span (scan width) controls to zero Hz.
NOTE
Geometric mean switching (on the 8 to 512 MHz bands) occurs near the middle of the frequency
range. Switching is controlled by the position of the FREQUENCY TUNE control and switches
between the high and low band filters for the frequency range. It can be noted either by listening
for actuation of the RF relays or by observing a change in the spectrum analyzer's display when
connected to the RF filters.
b. Adjust analyzer's center frequency controls for a frequency counter indication of the pass band frequency listed
in table. Adjust analyzer's vertical sensitivity controls to set trace to top (reference) graticule line on display (use
2 dB log per division); this sets the reference level for the filter check.
c. Set analyzer's frequency span controls as listed in the table. Connect test cables to RF filter input and output as
shown in the test setup. Check maximum loss at pass band frequency (center vertical graticule line) and below;
it should be as specified.
d. Set analyzer's frequency span controls to zero Hz. Adjust analyzer's center frequency controls for a frequency
counter indication of the stop band frequency listed in the table. Then reset frequency span controls as listed in
the table and set analyzer's display for 10 dB log per division.
NOTE
To measure the stop band frequency on the highest band it is necessary to set a frequency of
492 MHz at the second vertical graticule line to the left of center. This puts 692 MHz at the center
(the counter will only read to 550 MHz).
e. Check minimum loss at stop band frequency (center vertical graticule line) and above; it should be as specified.
f. If necessary, on the 64 - 512 MHz bands, adjust the appropriate filter components to set pass band and stop
band insertion loss within the specified limits. Use a non-metallic tuning tool.
NOTE The 256 - 512 MHz high band is the most difficult to adjust and usually takes many iterations. Start with
the adjustment capacitors oriented as in Figure 5-6. Stop band minimum loss should be >30 dB from 692 - 1000
MHz.
5-25
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