Butler_oscillator
The Butler oscillator is a crystal-controlled oscillator that uses the crystal near its series resonance point. They are used where a simple low-cost circuit is needed which can oscillate at high frquencies (>50MHz[1]) by using overtones of a crystal, and also giving low low phase noise.[2]
It was described by Butler in 1946 as the earthed grid oscillator, a derivative of the Hartley oscillator.[3] It is also known as the bridged-T oscillator or the grounded-base oscillator.[4]