Manual - 8500A Series Peak Power Meter - Giga-tronics

Series 8500A Peak Power Meters
Automatic Window Delay Selection Related Commands (Autoscaling)
* AUTO Autoscale Current Pulse Profile. If SRQ is enabled, it will be sent at the completion
of Autoscaling. Successful Autoscaling can be determined by checking the value of
the Status byte.
AVASnnn
Select the Number of Averages, n, for Autoscaling (1 to 999). This command can be
useful when attempting to Autoscale a pulse in a noisy environment. The more
stable the pulse to be Autoscaled is, the less averages required. This setting is
independent of other averaging settings such as AVCW or AVPK.
The number of averages set by this command is never reset to a default value (not
even by a Device Clear command). Therefore, it is advisable to set the desired value
prior to commencing the Autoscaling function, or to set it once at the beginning of
the program and not change its value again.
ASDLnnnnnn.n Select Maximum Expected Pulse Width for Autoscaling. The purpose of this
command is to allow autoscaling of narrow pulses with high repetition rates.
(n = 0.5 to 200,000 microseconds).
The maximum expected pulse width set by this command is never reset to a default
value (not even by a Device Clear command). Therefore, it is advisable to set this to
the desired value prior to activating the Autoscale function.
3.3.6 Marker Timing Measurements
A trigger must occur on a consistent basis to make repeatable pulse measurements for profiling
operations. Erratic pulse trains or profiles can lead to errors or confusion. In situations where pulse
widths or repetition rates are likely to continually vary, it would be better to make single pulse
measurements in the Peak Mode. However, to make single pulse measurements, you should know where
the Cursor Delay should be set to make the measurement.
The commands in the Automatic Timing description in this section allow for easy measurement of the
most commonly desired pulse parameters. These include rise time, fall time, pulse width and
combinations thereof. The automatic measurements are determined by conventions commonly used in the
microwave industry. For example, rise time would be from the 10% to 90% power points on the leading
edge of the pulse. However, there are still some gray areas which must be taken into account when you
use these automatic timing functions.
These gray areas include deciding what point on the pulse should be considered as the 100% power
reference point for the PPM to use when determining the rise time, fall time, and pulse width.
It is obvious that, in most situations, it is more desirable to use the center of the pulse as the reference
point. Special situations can, of course, occur where the setting of the reference point would be somewhat
arbitrary.
The PPM handles the above problems in two ways. The first method is when Autoscaling is used. The
Reference Power level is automatically set to a point more or less centered in time between the 3 dB
points on the pulse. The power axis of the display is also adjusted so that the point selected as the
reference point is set to the top of the display as 100%.
The second method is to allow you to set the Reference Power at some desired level. Power
measurements can be taken at different points along the top of the pulse to find the optimum point at
which to set the Reference Power. These decisions are based on the types of pulses it is expected will be
encountered.
3-26 Manual No. 20790, Rev C, November 1998
Superceded by Revision D, March 2009