The following schematic shows the Hartley Oscillator Basic Circuit Diagram. It is an electronic oscillator using two coils inductively coupled in serial, parallel to a single capacitor, forming the LC circuit that determines the frequency. This oscillator is very similar to the Armstrong oscillator. The difference between the Armstrong oscillator and the Hartley oscillator is that the tickler coil is part of the LC circuit. The Hartley oscillator was extensively used on all broadcast bands including the FM 88-108MHz band.
The following links provides detail information regarding Hartley Oscillator history, applications, design and simulation.
> Hartley oscillator Operation, History and Applications (ref: wikipedia.org)
> Designing a Hartley Oscillator (ref: electronics-tutorials.com)
> Hartley Oscillator Simulation (ref: falstad.com)