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comparator U512 does not toggle back and forth during a conversion, suspect either U512
or one of the clipping diodes
(CR500/CR501).
Note
Because currents are being summed at U512 pins 2 and 3, voltage levels at
these points are difficult to interpret.
Ramp
Counter
Refer to function block D of A3 Interface Assembly Schematic Diagram in the
HP 8560 E-Series Spectrum Analyzer Component Level Information.
The ramp counter is used for sweeps with widths greater than 2.0 MHz times N. The analog
sweep ramp is compared to the digital ramp counter. When the analog sweep ramp exceeds
the DAC output generated for that ramp counter setting,
HRAMP-COMP
toggles high,
indicating the end of a bucket. The ramp counter counts horizontal buckets. There are 601
buckets per sweep, so the ramp (bucket) counter counts from 0 to 600. The ramp counter is
incremented by HRST-PK-ENA.
1. Press
@GZi]
on the spectrum analyzer and set the controls as follows:
Span
............................................................
. MHz
Detector mode
................................................
SAMPLE
2. For spans greater than 2.0 MHz times NO, HODD (A3U525 pin 3) is a square wave with a
period defined by (2
x
sweep
time/600).
For example, for a 6
s
sweep time, HODD has a
period of 20 ms. The ramp (bucket) counter will be odd every other bucket.
ADC/lnterface
Section 6-27