2.11 High Power Measurements
One of the most important things to remember when using the PPM is that it employs balanced, zero
bias, Schottky diode detectors as power detectors. Due to this highly sensitive, highly accurate
configuration, the maximum power that the detectors can handle before burning out is +23 dBm
(200 mW). This limitation is regardless of duty cycle.
2.11.1
Power Warning - Max/Min Power Limits
The PPM has a built-in warning system to advise you of mild overloads to the detectors. Large overloads
which are usually the result of a failure in the device under test or leaving an attenuator out of the test
setup, cannot be prevented because of the speed at which these failures happen. However, you will be
advised by a prompt when the power level exceeds the preset power warning level.
The default value for the MAX Power warning point is +20.5 dBm. You can set this to anywhere between
-10 and +21 dBm.
The PPM also has a lower level limit (MIN). This is mainly used to avoid displaying power readings
outside the lower power range of the instrument. When the power level being measured by the PPM is
below the lower level limit, the readout will display a series of dashes to indicate that the power being
measured is too low for the PPM to take an accurate measurement.
The default value for the MIN Power warning point is -45.0 dBm. You can set this anywhere between -15
and -50 dBm. To change the MAX and MIN power limits, press [MENU] (7) [F1] [mm.mm] [dBm]
[nn.nn] [dBm], where mm.mm is the maximum power limit, and nn.nn is the minimum power limit.
2.12 High Power Measurement Procedures
The procedure for making absolute CW or Peak power measurements under high power conditions is as
follows:
1.
Approximate the Peak power of the signal to be measured.
2.
After 30 minutes warm-up, Self-Cal the PPM detectors.
3.
Choose an appropriate attenuator or coupler to be used in the test setup to reduce the power
being measured to a safe level for the detectors. The power at the detector input must be less
than +20 dBm.
4.
When making this approximation, be sure to use worst case power levels. If in doubt, a 10 dB
attenuator can be used directly on the detector input in addition to the selected high power
coupler or attenuator.
5.
Ensure that the RF power of the source to be measured is turned OFF.
6.
Connect the high power coupler to the RF source to be measured as shown in Figure 2-14. If a
high power attenuator is used, connect as shown in Figure 2-15.
7.
Connect the PPM detector with its attenuator to the coupled output of the high power coupler
(Figure 2-14), or to the output of the high power attenuator (Figure 2-15).
Operation
Manual No. 20790, Rev C, November 1998
2-37
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