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NOTE
NOTE
AM Noise Measurement Fundamentals
Calibration and Measurement General Guidelines
Calibration and Measurement General
Guidelines
Read This The following general guidelines should be considered when
setting up and making an AM-noise measurement.
•
The AM detector must be well shielded from external noise especially
60 Hz noise. The components between the diode detector and the test
system should be packaged in a metal box to prevent RFI interference.
The internal detectors in the Agilent/HP 70420A Option 001 and Agilent/HP
70427A, along with the Agilent/HP 70429A Option K21 provide this level
of protection.
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.
•
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.
•
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
The noise floor of the detector may degrade as power increases above
-- -
f
+15 dBm. Noise in the
about +10 dBm of drive level. The noise floor is best measured with
about +20 dBm of drive level.
•
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.
•
It should have the lowest possible noise figure, and the greatest possible
dynamic range.
•
The signal level must be kept as high as possible at all points in the test
setup to avoid noise floor degradation.
•
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.
12-6 Agilent Technologies E5500 Phase Noise Measurement System
1
region of the detector is best measured with
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f
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