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4
Phase Noise Basics
What is Phase Noise?
4-4
E5500 Phase Noise Measurement System Version A.02.00
Another useful measure of noise energy is L(f), which is then directly
related to
by a simple approximation which has generally
S φ f ( )
negligible error if the modulation sidebands are such that the total
phase deviation are much less than 1 radian (
Figure 4-2 CW Signal Sidebands viewed in the frequency domain
L(f) is an indirect measurement of noise energy easily related to the
RF power spectrum observed on an RF analyzer.
that the National Institute Science and Technology (NIST) defines
L(f) as the ratio of the power--at an offset (
carrier. The phase modulation sideband is based on a per Hertz of
bandwidth spectral density and or offset frequency in one phase
modulation sideband, on a per Hertz of bandwidth spectral density
(f)
and
equals the Fourier frequency or offset frequency.
power density in one phase modulation sideband
L f ( )
=
------------------------------------------------------------------------------------------------------------------------------------------ -
= single sideband (SSB) phase noise to carrier ration (per Hertz)
1
L f ( )
-- - S ∆φ f ( )
=
2
f)
(
total signal power
Document Part No. E5500-90024 Ed. 1.0
∆φ
<< radian).
pk
Figure 4-3
shows
Hertz away from the
)
P ssb
=
----------- -
P s
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