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Figure 9-1
● HINT 9:
Account for path losses
Adapters must be used if the connectors between the noise
source, DUT, and measurement system do not mate, as in
Figure 9-1. It is most important to avoid adapters where
the signal is smallest in the measurement setup. For
devices with gain, avoid adapters before the DUT.
For devices with loss, avoid adapters after the DUT.
Keep track of the insertion losses of adapters and
any additional components such as cables, baluns,
filters, pads, and isolators that are not part of the
DUT. These insertion losses have to be taken into account
by subtracting them from the measurement result. Any
adapters used between the noise source and the DUT
will introduce some loss, effectively reducing the ENR
of the noise source.
Modern noise figure analyzers can subtract these losses
from the measurement automatically. The analyzer
will also need to know the temperature of these
components and whether they are before or after
the DUT. The analyzer will correct the displayed noise
figure for all loss elements and their temperatures that
are entered.
Losses in the measurement system are corrected by user
calibration. Adapters and cables that are connected to the
instrument during both user calibration and measurement
are considered part of the measurement system and are
accounted for during user calibration.
If a pre-amp is needed prior to the measurement system
then choose a pre-amp with the correct connector
for the noise source, and include the pre-amp as part
of the calibration setup that measures the second stage
noise figure.