Manual - 8500A Series Peak Power Meter - Giga-tronics
Manual - 8500A Series Peak Power Meter - Giga-tronics
Manual - 8500A Series Peak Power Meter - Giga-tronics
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Remote Operation<br />
3.3.2 Measurement Data Correction<br />
The manner in which the PPM is able to make very fast peak power measurements is dependent on the<br />
usage of zero bias schottky diode detectors as power sensing elements. These diodes have typical<br />
rise-times of less than 10 nanoseconds making them useful for pulsed RF applications. However, at<br />
microwave frequencies, it is necessary to compensate for the detector’s non-linearity with frequency.<br />
Each <strong>Giga</strong>-<strong>tronics</strong> detector used in the PPM has a built-in PROM which contains frequency correction<br />
data. Depending on the mode of operation, the PPM can be instructed to automatically subtract out the<br />
frequency non-linearity error from the power measurement being made.<br />
The PPM needs to know the frequency of operation for this automatic correction to take place. This can<br />
be done at the front panel, over the GPIB, or by the use of the Voltage Proportional to Frequency feature<br />
(V α F). The V α F is an analog voltage connected to the PPM’s rear panel EXTERNAL FREQUENCY<br />
input connection. A voltage is usually available from most sweepers called V/GHz with a coefficient of<br />
1V/GHz. This voltage can be converted to digital information by the PPM, and used as a frequency input<br />
instead of having to enter it by some other means.<br />
In addition to automatic frequency correction, it may be desired in some applications to use manual<br />
corrections based on specific measurements rather than the factory-supplied data in the detector’s PROM.<br />
This is known as Cal Factor. (Some power meters on the market use the term % efficiency, but it is<br />
basically the same thing.) Cal Factor is expressed in dB, and is the amount of power that must be added<br />
to or subtracted from the measurement so that the data will be correct.<br />
Another Data Modifier called Offset can also be used. Complex microwave test setups sometimes include<br />
attenuators or couplers to reduce high power signals to safe levels that can be measured by delicate<br />
instruments such as the PPM. The Offset feature allows the subtraction of residual attenuator or coupler<br />
errors from the measurement.<br />
The preceding Data Correction commands will be discussed in the following sections.<br />
Detector PROM Correction: User Supplied Frequency<br />
FREQff.ff<br />
(Where ff.ff is the frequency of the correction.)<br />
Correction is determined by taking a user-supplied frequency (ff.ff) and referencing data in a PROM in<br />
the detector.<br />
Min Value: 0.01 GHz<br />
Max Value: 110.00 GHz<br />
Sample Program:<br />
10 ! THIS PROGRAM SETS THE<br />
20 ! FREQUENCY FOR DETECTOR<br />
30 ! RESPONSE CORRECTION FOR<br />
40 ! THE PPM<br />
50 !<br />
60 F=5.25 ! PPM FREQUENCY SETTING<br />
70 !<br />
80 ! SEND COMMAND TO PPM<br />
90 OUTPUT 704 USING 100; FREQ,F<br />
100 IMAGE 4A,DDD.DD<br />
110 END<br />
<strong>Manual</strong> No. 20790, Rev C, November 1998 3-17<br />
Superceded by Revision D, March 2009