AR 10008569, Operating And Service Manual, Page: 34 / 38

Models PH – Power Heads
Figure 6-1. Mismatch Uncertainty
6.2 EXAMPLE
The following example demonstrates how to calculate the total measurement uncertainty of power
measurement. The measurement conditions for this example are as follows:
The AR Model PM2002 Power Meter will be used with a Model PH2005 Power Head to measure a CW
signal. The signal will be at a level of –55 dBm and frequency of 7 GHz. The SWR of the source will be
1.50. Finally, we will assume a 5
°
C temperature change from time of calibration (calibration performed with
the 50 MHz, 0 dBm power reference on the PM2002).
1. We must establish the instrumentation uncertainty of the Model PM2002. The specification states 0.23%
at full scale or 0.46% at 1/10 of full scale. A level of –55 dBm will be a downscale point for range 0,
therefore, the 0.46% specification applies.
2. Since an auto calibration of our head was performed, we must add the uncertainty of our power reference.
For the 50 MHz, 0dBm reference, the worst case uncertainty is 1.20%.
20 Rev C