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6-24. 350kHz Bandpass Filter Test
This test checks the circuits in the signal path shown in Figure 6-16; in particular, it tests the
350kHz Bandpass Filter. A signal is input to the IF Input from an -hp- 3325A opt 001.
10MHz is input to the Reference Input. The Channel B output is measured with a scope.
Because the input frequency is sweeping from 340kHz to 360kHz, the envelope of the signal
on the scope represents the frequency response of the 350kHz Bandpass Filter about its
cutoff freqeuncy. The overall gain of the filter is adjusted while the scope is connected in this
manner. With the scope connected to various points within the filter, the filter shape is op
timized with several other adjustments. If the adjustments can be made, the test passes. The
results are printed.
Initializing the Test
If the Low Frequency Menu is displayed, press special function key 3 to initialize the test. If
the High Frequency Menu is displayed, press special function key 15, then select the Low
Frequency Menu and, finally, press special function key 3. After initialization, follow the in
structions displayed on the -hp- 9845B.
What if the Test Fails?
Assuming the previous tests have passed, the most likely cause of failure is the 350kHz
Bandpass Filter. The operation of Lll can be confirmed using "SWITCH". Refer to Ser
vice Group One for schematics, component locators and circuit descriptions.
Equipment Set Up
Remove the top cover for this adjustment. The oscilliscope is
connected to each stage of the band pass filter at the Test
points given below.
3325
SIGNAL
Q
A
A
Z BLANK
TTL
O
35601
o O
o
o
o °
o
IF INPUT
FROM 3585
~ A ~
~W
| 3455
I
I
o
o
[I.]
MARKER
TTL
6-36
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