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12
AM Noise Measurement Fundamentals
Calibration and Measurement General Guidelines
12-8
E5500 Phase Noise Measurement System Version A.02.00
Also, the AM detector should be connected directly to the test
system if possible, to minimize ground loops. If the AM detector
and test system must be separated, semi-rigid cable should be
used to keep the shield resistance to a minimum.
G
Although AM noise measurements are less vulnerable than
residual phase-noise measurements to noise induced by vibration
and temperature fluctuation, care should be taken to ensure that
all connections are tight and that all cables are electrically sound.
G
The output voltage monitor on the AM detector must be
disconnected from digital voltmeters or other noisy monitoring
equipment before noise measurement data is taken.
1
G
The noise floor of the detector may degrade as power increases
-- -
f
above +15 dBm. Noise in the
measured with about +10 dBm of drive level. The noise floor is
best measured with about +20 dBm of drive level.
G
An amplifier must be used in cases where the signal level out of
the DUT is too small to drive the AM detector or is inadequate to
produce a low enough measurement noise floor. In this case the
amplifier should have the following characteristics.
G
It should have the lowest possible noise figure, and the greatest
possible dynamic range.
G
The signal level must be kept as high as possible at all points in
the test setup to avoid noise floor degradation.
G
It should have only enough gain to get the required signal levels.
Excess gain leads to amplifiers operating in gain compression,
increasing their likelihood of suppressing the AM noise to be
measured.
G
The amplifier's sensitivity to power supply noise and the supply
noise itself must both be minimized.
1
region of the detector is best
-- -
f
Document Part No. E5500-90024 Ed. 1.0
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