Hp 84125C Test-Set Uncertainties - HP 84125C User Manual

HP 84125C Test-Set Uncertainties

A-2 Amplitude Accuracy
Antenna factor uncertainty
uncertainty of characterizing the antenna factor.
Antenna mismatch uncertainty
created when the antenna is connected to the test-set input. The
magnitude of this error depends on the VSWR of both the antenna
and the test set.
Calibration data uncertainty
the factory calibration of the HP 84125C test set at the calibration
frequencies.
Test-set atness uncertainty
the spectrum analyzer input and test-set output plus the maximum
interpolation error that occurs when making measurements at
frequencies other than the calibration frequencies.
Test-set repeatability uncertainty
by the RF cable assembly being exed, the ampli ers drifting
between calibrations, and the repeatability of the connectors used
to interconnect the lters and the antennas.
Test-set maximum temperature drift uncertainty
amplitude error that will occur due to temperature drift. This
error is valid when the HP 84125C system is used in an ambient
temperature range of 20 C to 30 C.
To calculate the total amplitude uncertainty, the individual
uncertainties described above must be combined. In combining them,
we recommend following the procedure in the National Measurement
Accreditation Service (NAMAS), Publication NIS 81. (NAMAS is now
known as United Kingdom Accreditation Service, UKAS.)
This publication speci cally addresses the calculation of measurement
uncertainty in EMC measurements. This procedure involves the
following steps:
1. Determine the type of each uncertainty and its probability
distribution.
2. Convert each uncertainty to a \standard" uncertainty. Refer to
NAMAS, publication NIS 81.
3. Combine the standard uncertainties by either using Root Sum
Square (RSS) or direct addition depending on whether it is random
or systematic, and whether or not they are correlated with each
other.
4. Multiply your result by a factor (typically 1 to 3) to arrive at the
desired con dence level for your measurement. The following
example, uses 2 which is recommended by NAMAS, Publication
NIS 81. This factor corresponds to a con dence level of 95%.
The following example uses the 1 to 18 GHz antenna with the
spectrum analyzer in Logarithmic-scale mode (
NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN
.
is the antenna manufacturer's
is caused by the VSWR pattern
is a measure of the uncertainty of
includes the mismatch error between
consists of the errors caused
AMPLITUDE
4
is a maximum
,
5