Agilent Technologies 4395A, Manual Change

Page: 398 / 575

Spectrum Measurement Basics
Noise measurement
Noise F ormat and Marker Noise F orm
When a spectrum analyzer measures noise , the power shown by an analyzer is in proportion
to RBW (because spectrum analyzers measure total power coming thorough RBW). F or noise
measurement, the measurement value is usually normalized by an equivalent noise bandwidth
of an RBW lter (frequency). The noise format automatically normalizes noise power by the
equivalent noise bandwidth and displays the trace on the screen. The marker noise form also
reads out the noise level normalized, even if the format is the spectrum.
Sample Detection Mode for Noise Measurement
F or noise measurement, the sample detection mode is best. Because the power of noise
is uniformly distributed over frequency , it is not necessary to measure all the frequencies
between the display points . It is sucient to measure only the display points . This is why the
sample detection mode is used for noise measurement.
VB W for Noise Measurement
Y ou should specify a smaller VBW when using the 4395A to measure noise levels .
T o obtain accurate noise level measurements , it is essential to determine the average value
over a relatively long period. With a smaller VBW , the 4395A can determine the average time
domain at each measurement point.
A-22 Basic Measurement Theory