7-6
Typical one-sided spectral density of phase deviation vs. offset frequency, for various standards, calculated at 5 MHz.  L(f) = ½ Sf 
-30
-40
-50
-60
-70
-80
-90
-100
-110
-120
-130
-140
-150
-160
-3
-2
-1
0
1
2
3
4
Text Box: 10*Log(Sf(f))
10*Log(Sf(f))
Log (f)
Text Box: Cesium
Cesium
Text Box: Quartz
Quartz
Text Box: Hydrogen Maser
Hydrogen Maser
Text Box: Rubidium
Rubidium
Phase Instabilities of Various Frequency Standards
The above graph  is based on one prepared and provided by Richard Sydnor, Jet Propulsion Laboratory, 1989.