Giga-tronics 8501A, Руководство по эксплуатации и техническому обслуживанию

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time.
The easiest way to ensure that all of the Peak Mode settings are at their default values is to
select Peak operation after initializing the current setup. Press [MEM] (3) [F1] [PEAK]. The
display should be similar to Figure 2-6.
A display of hyphens in place of a number in the power read-out portion of the display indicates
that the power being sampled is below the measurement range of the system. Either the overall
power of the pulse is too low, or the cursor has not been placed on a sufficiently high powered
section of the pulse of interest. Another possibility could be no RF present. However, in this
case, the PPM would not be triggering if Internal Triggering were being used and there was not
enough RF at the detector input.)
☛
NOTE: If the External Trigger mode is being used, the likelihood of obtaining a meaningful
power reading at this point depends on the timing relationship between the RF pulse at the
detector input and the external trigger pulse coming in through the rear panel input
connection of the instrument.
If the trigger pulse and the RF pulse are coincident in time, then the default Cursor Delay time
of 1
µ
s will probably result in the Cursor being located somewhere on the pulse. This depends
on the pulse width exceeding 1
µ
s.
It is recommended that Internal Trigger is used before using the External Trigger mode so that
pulse information such as pulse width can be obtained. This can save the effort of having to
search for the pulse using the Cursor Delay function — Using the Graph Mode makes searching
much easier.
5.
As already mentioned, the cursor (
∆
symbol) next to the DLY indication on the display means
that the spin knob is active and, if turned, will alter the value of the Cursor Delay (CSR DLY).
To locate the highest power point on the pulse, it is best to start at the rising edge of the pulse
and move the cursor gradually up in time until the power reading reaches its maximum point.
This can be done as follows:
a. Turn the spin knob counter clockwise until the Cursor Delay is zero (i.e. DLY = 0.000 ns on
the display).
b. Slowly rotate the spin knob clockwise while monitoring the power readout display. Note that
the increments that the spin knob causes the DLY to step through will change faster as the
knob is turned faster. Rotate the knob until the power readings increase. This indicates that
the leading edge of the measured pulse being is being monitored.
c. Continue increasing the Cursor Delay until the power readings go through a peak or stay at a
high level. If the maximum power point is passed, turn the knob counterclockwise slowly,
thus reducing the cursor delay until the maximum reading is once again reached.
d. Press [FREQ] and enter either the desired RF operating frequency or the Cal Factor in dB as
required. (This step is not necessary if the external frequency input mode is in use.)
e. Enter any required dB Offset (see Section 2.6.2).
f. The power will be displayed similar to Figure 2-6. The desired unit of power measurement
can be selected by pressing [dB/mW].
6. If difficulties arise in locating the pulse to be measured, use the Graph Mode with Autoscale.
Series 8500A Peak Power Meters
2-22
Manual No. 20790, Rev C, November 1998