Variable Gain Amplifier (VGA)
See function block AB of A3 Interface Assembly Schematic Diagram (sheet 6 of 6).
The VGA provides adjustable gain in the video path. Its nominal gain of 7 can be adjusted
U112 removes dc offset to keep U113 in its monotonic range. (Both U112 and U113
are set to the same value.) The DAC settings cannot be changed from the front panel.
Track and Hold
See function block AC of A3 Interface Assembly Schematic Diagram (sheet 6 of 6).
1. Press
on the HP 8560A and set the controls as follows:
C E N T E R F R E Q
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...300 MHz
SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DETECTOR MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sample
REF LVL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -70
LOG
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SWEEP TIME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50ms
2. Disconnect any signal from the analyzer input. A full scale display of sampled noise should
be present.
3. Trigger an oscilloscope on the positive going edge of HHOLD
pin 16).
4. The waveform at
should be random noise with an average level of approximately
4 V. The noise should have a flat spot in its response while HHOLD is high, indicating
proper operation of U114.
Section 7-21
Summary of Contents for 8560A
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