3.3.2 Measurement Data Correction
The manner in which the PPM is able to make very fast peak power measurements is dependent on the
usage of zero bias schottky diode detectors as power sensing elements. These diodes have typical
rise-times of less than 10 nanoseconds making them useful for pulsed RF applications. However, at
microwave frequencies, it is necessary to compensate for the detector’s non-linearity with frequency.
Each Giga-tronics detector used in the PPM has a built-in PROM which contains frequency correction
data. Depending on the mode of operation, the PPM can be instructed to automatically subtract out the
frequency non-linearity error from the power measurement being made.
The PPM needs to know the frequency of operation for this automatic correction to take place. This can
be done at the front panel, over the GPIB, or by the use of the Voltage Proportional to Frequency feature
(V α F). The V α F is an analog voltage connected to the PPM’s rear panel EXTERNAL FREQUENCY
input connection. A voltage is usually available from most sweepers called V/GHz with a coefficient of
1V/GHz. This voltage can be converted to digital information by the PPM, and used as a frequency input
instead of having to enter it by some other means.
In addition to automatic frequency correction, it may be desired in some applications to use manual
corrections based on specific measurements rather than the factory-supplied data in the detector’s PROM.
This is known as Cal Factor. (Some power meters on the market use the term % efficiency, but it is
basically the same thing.) Cal Factor is expressed in dB, and is the amount of power that must be added
to or subtracted from the measurement so that the data will be correct.
Another Data Modifier called Offset can also be used. Complex microwave test setups sometimes include
attenuators or couplers to reduce high power signals to safe levels that can be measured by delicate
instruments such as the PPM. The Offset feature allows the subtraction of residual attenuator or coupler
errors from the measurement.
The preceding Data Correction commands will be discussed in the following sections.
Detector PROM Correction: User Supplied Frequency
FREQff.ff
(Where ff.ff is the frequency of the correction.)
Correction is determined by taking a user-supplied frequency (ff.ff) and referencing data in a PROM in
the detector.
Min Value: 0.01 GHz
Max Value: 110.00 GHz
Sample Program:
10 ! THIS PROGRAM SETS THE
20 ! FREQUENCY FOR DETECTOR
30 ! RESPONSE CORRECTION FOR
40 ! THE PPM
50 !
60 F=5.25 ! PPM FREQUENCY SETTING
70 !
80 ! SEND COMMAND TO PPM
90 OUTPUT 704 USING 100; FREQ,F
100 IMAGE 4A,DDD.DD
110 END
Remote Operation
Manual No. 20790, Rev C, November 1998
3-17
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