Editing Variable-frequency oscillator (section)

===Purity===
{{Further|Spurious emission}}
A plot of a VFO's amplitude vs. frequency may show several peaks, probably [[harmonic]]ally related. Each of these peaks can potentially [[Frequency mixer|mix]] with some other incoming signal and produce a ''spurious'' response. These ''spurii'' (sometimes spelled ''spuriae'') can result in increased noise or two signals detected where there should only be one.<ref name="arrlhandbook" /> Additional components can be added to a VFO to suppress high-frequency parasitic oscillations, should these be present.

In a transmitter, these spurious signals are generated along with the one desired signal. Filtering may be required to ensure the transmitted signal meets regulations for bandwidth and spurious emissions.