Specifications
8
A Y-Factor noise figure analyzer assumes a linear
change in the detected noise power as the noise source
is switched between T
hot
and T
cold
. Any variations
from linearity in either the DUT or in the detector directly
produce an error in the Y value and hence in the noise
figure that is displayed. The instrumentation uncertainty
specification accounts for the linearity of the analyzer’s
detector. The linearity of the DUT, however, should be
carefully considered when making the measurement.
The measured noise figure is determined by the power in
the instrument’s resolution bandwidth. The instrument’s
attenuation settings, however, may be determined by
the power in the instrument’s overall frequency range
that reaches the range detector. The analyzer is therefore
susceptible to being overdriven by noise outside the
bandwidth of any one individual measurement, and
therefore vulnerable to non-linearity errors. In such
cases, attenuate any broadband power outside the
analyzer’s resolution bandwidth. Use a filter wider than
the measurement frequency range and before the DUT.
Consider measuring a familiar “reference” or “gold
standard” device at the beginning of each day to assure
that the same result is obtained as prior days for the same
device, to add assurance that the measurement instrument
is warmed up sufficiently.
● HINT 5:
Avoid non-linearities
Avoid all predictable sources of nonlinearities:
• circuits with phase lock loops (and any circuit
that relies on signal presence to set its operating
condition)
• circuits that oscillate (even if at a far-removed
frequency)
• amplifiers or mixers that are operating
near saturation
• AGC circuits or limiters (AGC circuits have been
known to contribute additional noise power at the
power levels near its operational point, even when
disabled.)
• High Gain DUT’s without in-line attenuation
(Attenuate the output of the DUT if necessary.
See Hint 7 for details)
• power supply drifts
• DUTs or measurement systems that have not
warmed up
• logarithmic amplifiers (The standard Y-Factor
measurement is invalid for amplifiers in a logarithmic
mode.)