External Marker Adjustment - HP 83522A Service Notes

Adjustments
ADJUSTMENTS
Model 83522A
5-27. MARKER AND SAMPLER ADJUSTMENTS (Cont'd)
7. Press
(
.
Connect the oscilloscope probe to A7TP2. First, ensure that
marker OFF pulses exist on both sides of the marker ON pulse. (Decreasing the
oscilloscope BEAM INTENSITY will expose the marker ON pulses.) (See Figure 5-37.)
While the crystal markers may function properly without them, the marker-off pulses
provide a safeguard against false markers appearing on the display.
8. Secondly, ensure that the marker OFF pulse does not overlap the marker ON pulse.
Figure 5-38 illustrates an improper marker OFF pulse. When this occurs, change the
value of A7R4 to eliminate overlap. The optimum value for A7R4 allows the maximum
number of marker OFF pulses without overlapping the ON pulse. The typical value for
A7R4 is 1200 Ohms and the minimum value is 1000 Ohms. (To observe marker OFF
pulses, vary RF OUTPUT power between +3 dBm and +13 dBm.)
Figure 5-3 7. On/Off Pulse of
Correctly Adjusted Circuit
ONIOFF PULSE OVERLAP
Figure 5-38. On/Off Pulse of
Misadjusted Circuit Showing Overlap
5-28. EXTERNAL MARKER ADJUSTMENT
REFERENCE:
Service Sheet: A8
DESCRIPTION:
A rear panel BNC jack is available for external marker sources. A8R67 provides gain
adjustment to the video amplifier for marker presence.
When using the 8755C with external markers, factory select resistor A8R28 prevents the
feedthrough of 27.8 kHz square wave onto the marker birdie. Increasing the value of A8R28
reduces the feedthrough problem, but degrades internal markers.