Giga-tronics 8501A, Operation & Maintenance Manual

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Waiting for trigger on A (or B) Detector Signal
F1 for Trig Mode or Level Change
F3 for CW Data Display
If you still desire to Autoscale at this point, the easiest thing to do is to increase the RF power
until the power at the detector input is greater than the trigger level. Then the system will start to
trigger and the autoscaling process will begin.
The factory-set default initial delay is 75
µ
s (pulses wider than 75
µ
s or pulses less than 75
µ
s
apart cannot be Autoscaled when using the default setting), and the default pulse averaging is
four samples for the Autoscaling function. This can be changed to allow the user to enter a
different pulse width and averaging number by accessing Menu-9 (press the MENU key 9 times),
and then following the prompts given in that menu. Once the pulse width and/or pulse averaging
has been changed from the default setting, the values will remain at the new setting whenever the
instrument is turned off and on again. The values are not affected by recalling set-ups, nor at
power-on.
3. If the previous triggering requirements have been met, the PPM will display the statement,
AUTOSCALING IN PROGRESS
4. When the Autoscaling has successfully completed, the pulse profile will be centered in the
graphics display area on the left side of the window and the top of the pulse will line up with the
100% tic mark. The Cursor (displayed as a vertical line with spaces just above and below the
point where it crosses the pulse) will be located at the center of the pulse profile. If all of the
above has occurred, you can go to the Power Display instructions given below.
Due to the many varieties of pulse widths, pulse shapes, and duty cycles that might be encountered, it is
not always possible for the PPM to autoscale. If the failure to autoscale is the result of a pulse being
present at the 75
µ
s default setting, the setting can be changed by accessing Menu-9, making the change,
and then repeating the autoscaling procedure detailed in this section. It is necessary to keep the initial
delay less than the time from the trigger to the start of the second pulse since the Autoscale routine
cannot handle multiple pulses in the delay window.
Autoscaling Procedure - External Trigger
When pulses are autoscaled on an external trigger, the PPM uses the internal trigger level of the selected
detector to find the pulse. For this reason, the internal trigger level of the selected detector must be lower
than the maximum power of the pulse. A good test is to first select internal trigger and verify that the
PPM is triggering before trying external trigger autoscaling.
The external triggered autoscale will set the Start Delay to center the pulse in the delay window.
However, autoscaling may not work properly if the pre-trigger is more than ten times the pulse width.
1. Press [PEAK]. The PPM will now display the power reading at the Cursor location in large
alphanumeric characters, similar to the display shown in Figure 2-6. The statement
DLY = n.nnn
µ
s
will be at the bottom of the display. This is the Cursor Delay which indicates the time difference
between the pulse’s initial triggering point and the point where the reading was taken. If the
triggering method is changed, a given Cursor Delay does not necessarily guarantee that the
power reading will be taken at exactly the same point on the pulse as it was before.
Series 8500A Peak Power Meters
2-20
Manual No. 20790, Rev C, November 1998