HP 8642A Operating Manual page 92

Model 8642A/B
Operation
RF Frequency Sweep (cont'd)
DC FM with Phase Continuous Frequency Sweep
During Phase Continuous Frequency Sweep (Special Function 12 3), dc-coupled FM is not
possible when either DC FM Update Mode (Special Function 11 7) or DC FM Correction
(Special Function 216) is selected.
Zero Span for Stepped Frequency Sweep
To calculate the number of X-axis steps automatically selected for zero span using
Stepped Frequency Sweep, refer to calculation # 1 on page 3-53. To calculate a sweep
time that could be selected for a desired number of X-axis steps, refer to calculation # 3
on page 3-54. The maximum number of X-axis steps is 102 3 (or 1024 points).
Zero Span for Phase Continuous Frequency Sweep (Special Function 123)
To calculate the number of X-axis steps automatically selected for zero span using Phase
Continuous Frequency Sweep, refer to calculation # 5 on page 3-62.
X AXIS
A 0V to +10V stepped output is available at the X AXIS output connector on the rear
panel. The frequency points at the output coincide with the points in the sweep time
calculations for Stepped Frequency Sweep. For Phase Continuous Frequency Sweep,
frequency changes in a phase continous manner while the X-axis output changes in steps.
Z AXIS
A blanking pulse is available at the Z AXIS output. (The blanking pulse is TTL positive
true for CRT blanking during retrace.)
There is a time that occurs between the end of the sweep and the beginning of the next
sweep while the Z AXIS output is blanked and the frequency and X AXIS output are
being reset. This time is called start-of-sweep settling time. Start-of-sweep settling
time is not included in the sweep time setting. Also, start-of-sweep settling time is not
selectable.
For Stepped Frequency Sweep, this settling time is approximately 1 2% of sweep time with
a minimum of 100 ms and a maximum of 600 ms (this time can be reduced by
approximately half when you select Special Function 11 9, Disable Settling).
Normally, for Phase Continuous Frequency Sweep, the settling time is approximately 1 2%
of the sweep time. However, for sweep times less than 75 ms, the settling time can be
equal to or slightly greater than the sweep time itself (depending on the sweep span). For
sweep times greater than 7 5 ms, the settling time gradually approaches 1 2% of the sweep
time. Minimum settling time is 1 5 ms, maximum settling time is 500 ms.
HP-IB. Sequence Dependency
RF frequency sweep settings are sometimes coupled with other functions. Therefore,
HP-IB codes may need to be entered in a particular sequence when accessing
combinations of these functions. Refer to the discussion about Sequence Dependency,
which begins on page 3-12 in the HP-IB portion of this Section III.
3-65