Vackář oscillator

In 1949, the Czech engineer Jiří Vackář published a paper on the design of stable variable-frequency oscillators (VFO).

[2] The paper discussed many stability issues such as variations with temperature, atmospheric pressure, component aging, and microphonics.

[3] Larger tuning ranges require switching stable fixed capacitors or inductors.

It is possible to make wide range VFOs with stable output amplitude by heavily damping (loading) the tuned circuit, but that tactic substantially reduces the Q and the frequency stability.

Vackář concluded that the Clapp oscillator "can only be used for operation on fixed frequencies or at the most over narrow bands (max.

[10] Vackář then describes an oscillator circuit due to Radioslavia in 1945 that maintained "a comparatively constant amplitude over a wide frequency range.

[14] Vackář describes a VFO design using this circuit that covers a modest frequency range of 1:1.17.

Vackář based his design on stability analysis of Gouriet-Clapp (Vackář claims it is for fixed frequency or a very narrow band, max 1:1.2), Seiler[19] and Lampkin[20] oscillators (in the Lampkin's, an inductive voltage divider on the tuned circuit coil is used instead Cv, Cg, and Ca of Seiler's; schematics in the 1st ref).

The oscillator's stability is due largely to the dependency of the tube's (or transistor's) forward transconductance on the resonant frequency (ω) of the tuned circuit.

Schematic of what is commonly called the Vackář oscillator. Vackář credited Radioslavia with developing this circuit in 1945. ^{[

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