Editing Variable-frequency oscillator (section)

===Stability===
Stability is the measure of how far a VFO's output frequency drifts with time and temperature.<ref name="clark_and_hess"/> To mitigate this problem, VFOs are generally [[phase-locked loop|"phase locked"]] to a stable reference oscillator. PLLs use [[negative feedback]] to correct for the frequency drift of the VFO allowing for both wide tuning range and good frequency stability.<ref>{{Cite web 
| url = http://www.mwrf.com/Articles/Index.cfm?ArticleID=22026&pg=2
| author=Hittite Microwave Corp
| title=Compact PLLs Integrate VCOs 
| year=2009 
| publisher=Microwaves & RF Magazine}}
</ref>