Boonton Power Sensor - Manual (Page 42)

Calibrator Level Uncertainty. This term is the uncertainty in the calibrator’s output level for
a given setting for calibrators that are maintained in calibrated condition. The figure is a
calibrator specification which depends upon the output level:
50MHz Calibrator Level Uncertainty:
At 0 dBm: ± 0.055 dB (1.27%)
+20 to -39 dBm: ± 0.075 dB (1.74%)
-40 to -60 dBm:
± 0.105 dB (2.45%)
1GHz Calibrator Level Uncertainty:
± (0.065 dB (1.51%) at 0 dBm + 0.03 dB (0.69%) per 5 dB from 0 dBm)
The value to use for calibration level uncertainty depends upon the sensor calibration
technique used. If AutoCal was performed, the calibrator’s uncertainty at the measurement
power level should be used. For sensors calibrated with FixedCal, the calibrator is only used
as a single-level source, and you should use the calibrator’s uncertainty at the FixedCal level,
(0dBm, for most sensors). This may make FixedCal seem more accurate than AutoCal at
some levels, but this is usually more than offset by the reduction in shaping error afforded by
the AutoCal technique. (Refer to the Instruction Manual of the instrument in use for
calibrator level uncertainty.)
Calibrator Mismatch Uncertainty. This term is the mismatch error caused by impedance
differences between the calibrator output and the sensor’s termination. It is calculated from
the reflection coefficients of the calibrator (D
CAL
) and sensor (D
SNSR
) at the calibration
frequency with the following equation:
Calibrator Mismatch Uncertainty = ±2 * D
CAL
* D
SNSR
* 100 %
The calibrator reflection coefficient is a calibrator specification:
Internal Calibrator Reflection Coefficient (D
CAL
): 0.024 (at 50MHz)
External 2530 Calibrator Reflection Coefficient (D
CAL
): 0.091 (at 1GHz)
The sensor reflection coefficient, D
SNSR
is frequency dependent, and may be looked up in
Section 2 of this manual. (Refer to the Instruction Manual of the instrument in use for
calibrator SWR specifications.)
Source Mismatch Uncertainty. This term is the mismatch error caused by impedance
differences between the measurement source output and the sensor’s termination. It is
calculated from the reflection coefficients of the source (D
SRCE
) and sensor (D
SNSR
) at
the measurement frequency with the following equation:
Source Mismatch Uncertainty = ±2 * D
SRCE
* D
SNSR
* 100 %
The source reflection coefficient is a characteristic of the RF source under test. If only the
SWR of the source is known, its reflection coefficient may be calculated from the source
SWR using the following equation:
Source Reflection Coefficient (D
SRCE
) = (SWR - 1) / (SWR + 1)
Power Sensor Manual 35 37