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n
Etc, Erc = effective crosstalk
n
Efl,
Erl = effective load match
n
Eft, Ert
=
effective transmission tracking
w
Cnn, Ctm = cable stability
(deg./GHz)
n
Abl,
Ab2
=
dynamic accuracy
n
F
=
frequency
The sources for dynamic accuracy error effects are from errors during internal self-calibration
routines, gain compression in the microwave frequency converter (sampler) at high signal
levels, errors generated in the synchronous detectors, localized non-linearities in the IF
illter
system, and from
Lo
leakage into the IF signal paths.
Sources of
Random
Errors
The random error sources are noise, connector repeatability and dynamic accuracy. There are
two types of noise in any measurement system: low level noise (noise floor) and high level
noise (phase noise of the source).
Low level noise is the broadband noise floor of the receiver which can be reduced through
averaging or by changing the IF bandwidth.
High level noise or jitter of the trace data is due to the noise floor and the phase noise of the
LO source inside the test set.
Connector repeatability is the random variation encountered when connecting a pair of RF
connectors. Variations in both reflection and transmission can be observed.
The listing below shows the abbreviations used for random errors in the error models and
uncertainty equations.
w
Rnt
= raw noise on trace (rms)
n
Rnf = raw noise on floor (rms)
n
Crrl
= port 1 connector reflection repeatability error
n
Crtl
=
port 1 connector transmission repeatability error
n
Crr2
= port 2 connector reflection repeatability error
n
Crt2
= port 2 connector transmission repeatability error
Sources of Drift
Errors
Drift has two categories: frequency drift of the
signal
source and instrumentation drift.
Instrwnentation
drift affects the magnitude and phase of both reflection and transmission
measurements.
The
primary
causes for instrumentation drift are the thermal expansion characteristics of
the interconnecting cables within the test set and the conversion stability of the microwave
frequency converter.
The list below shows the drift errors in the error models and uncertainty equations.
w
Dmxbx, Dmsax = drift magnitude
n
Dpxbx, Dpsax
=
drift phase
w
Dpfxbx, Dpfsax
=
drift phase/f
B-2
Determining System Measurement Uncertainties