Chapter 8 453
IF Section
Cal Oscillator Assembly (P/O A4)
300 Hz to 3 kHz Resolution Bandwidth Out of
Specification
1. If the 3 dB bandwidth of one of these filters is incorrect, suspect a
failure of one of the five available sweeps from the sweep generator
in the cal oscillator (function block Z). These sweeps are generated
by changing the switch settings of A4U803 which routes signals
through A4U802 and A4U804.
2. Disconnect W52 (coax 9) from A4J8.
3. Connect the source connection of a 3 dB power splitter (Minicircuits
Model: ZSC J-2-1) to A4J8. Connect one output of the power splitter
to the input of an HP 8566A/B spectrum analyzer. Connect the other
output of the power splitter to cable W52 (coax 9).
NOTE Ifa3dBpower splitter is not available, an SMB tee and an active probe
may be substituted. Connect the active probe between the tee and the
other spectrum analyzer. The absolute power levels are approximately
3 dB higher than those stated below, due to the elimination of the 3 dB
power splitter.
4. Press
INSTR PRESET on the HP 8566A/B and set the controls as
follows:
Center frequency .................................................... 10.8MHz
Span .................................................................................0Hz
Reference level ......................................................... −43dBm
Resolution bandwidth .............................................. 100kHz
Video bandwidth ......................................................... 10kHz
Sweep time .................................................................... 50ms
Scale ......................................................................... 1dB/DIV
Sweep ............................................................................ Single
5. On the spectrum analyzer, press
PRESET and CAL.
6. Press
FULL IF ADJ. When the display reads ADJUSTING IF:
10 kHz RBW, press
SINGLE on the HP 8566A/B.
7. The HP 8566A/B screen illustrates frequency versus time of the cal
oscillator output sweeps. See Figure 8-16 on page 455. The slope of
the HP 8566A/B 100 kHz resolution bandwidth is used to detect
frequency changes. Sweeps that vary (greater than 30%) from the
normal levels, trigger error code ERR 581 or ERR
582.
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