MM0474
(2) Calibration Factor. Calibration Factor is the ratio of substituted
audio or DC power in a thermistor mount to the microwave RF power incident upon
the mount.
Calibration Factor is a figure of merit assigned to a thermistor mount to
correct for the following sources of error: 1) RF reflected by the mount due to
mismatch, 2) RF loss caused by absorption within the mount but not in the
detection thermistor elements, and 3) DC-to-microwave power substitution error.
Calibration Factor is applied as a connection factor to all measurements made
without a tuner. When these factors and thermoelectric effect are taken into
consideration, the power indicated is the power that would be delivered by the
RF source to the characteristic impedance of the transmission line. The total
SWR in the transmission line determines a region of uncertainty about the
measured power.
(3) Effective Efficiency.
Effective Efficiency is the ratio of
substituted audio or DC power in a thermistor mount to the microwave RF power
dissipated within the mount.
Effective Efficiency corrects for power absorbed in parts of the mount other
than the detection thermistor elements and DC-to-microwave power substitution
error in the thermistor mount. Effective Efficiency is applied as a correction
factor when a tuner is used to match the thermistor mount to the transmission
line or RF source. In this case, all of the RF power incident upon the mount
is absorbed in the mount, measurement uncertainty due to mount SWR is
eliminated; however, losses in the tuner must be considered.
j. Calibration Data Application.
When the 486A is used with Model 431 or 432 Power Meters, Calibration
Factor or Effective Efficiency corrections can be made by setting a front panel
switch.
With the proper setting, the 431 or 432 compensates for the
Calibration Factor or Effective Efficiency in the 486A. If the 486A is used
with a power meter other than the 431 or 432, Calibration Factor or Effective
Efficiency corrections can be made by dividing the measured power by the
Calibration Factor or Effective Efficiency value respectively.
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