Neelandan writes –

I am assembling this to find out the limit of oscillation frequency of a transistor from my junk box. After it is completed, it shall be used as a signal source for some uhf circuits.

The frequency of the oscillator depends upon a tuned circuit – a parallel connection of an inductor and a capacitor. I shall not use a separate capacitor, depending on the capacitance of the wiring and the internal capacitance of the transistor for this function. The inductor shall be made pluggable, so that I can use successively smaller inductors until the circuit stops oscillating. The smallest inductor which still allows the circuit to work should produce the highest frequency.

For supporting the inductor, I am using a small scrap of board soldered at right angles to a larger piece, and supported by struts of connector pins soldered in. The sockets shall be pins extracted from an IC socket. The components shall be placed close together to minimise inductance so that the highest frequency may be attained.

It all starts with a circuit diagram – I have alloted about two thirds of the supply voltage as Vce and around 5 ma of collector current with a supply voltage of 12V.

instructables : UHF oscillator – Link.