UHF Oscillator

A single transistor minimum component oscillator generating signals in the ultra high frequency range - a few hundreds of Megahertz.

I have measured its frequency here: https://www.instructables.com/id/Frequency-measurement-by-Lecher-Line/

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.

M/s Freescale just provided the post-it note I used to draw this circuit. They do not endorse or recommend this circuit in any way.

The socket to accept the inductor, the transistor and the base bypass capacitor (1nf) has been connected up. The circuit diagram is highlighted to show the components on board. The wire inserted into the pair of sockets is just a dummy to keep them from falling off when the solder is heated for soldering something else.

The resistors have been soldered in next. They are not that critical, however, in order to keep the assembly compact so that another stage or device can be fitted to the board later, they have been squeezed together against the transistor.

A ferrite bead (piece of ferrite core with a hole down the middle) has been placed over the lead of the emitter resisor to form a small inductor there.

Frequently, while taking apart old rf gear, I come across these coils which have ferrite cores in them. Some of those cores have holes through them and they get saved as ferrite beads.

The circuit is now finished, and a piece of wire is plugged in forming an inductor. It works, as you can see by viewing the attached movie.

You see three people walking along the street (probably to a wedding). You stop one of them.

You pull out this little baby from your pocket.

"Look at this thing! It is an Ultra High Frequency Oscillator".

"A What? " He asks, nervously glancing ahead at the lucky two who managed to get away.

"You know, it generates a signal which alternates in polarity more than a few hundred million times per second!"

This information, unfortunately, does not seem to impress that unfortunate wedding guest much. You get the same sort of treatment the ancient mariner must have gotten, when wandering around with his tale of the dead albatross.

OK. What is this thing good for, exactly?

My intention in building it was to get a signal source to sort my collection of ancient and modern transistors to two piles - one pile of devices usable at high frequency and the other, not.

What is the frequency of oscillation? What is the power output?

I do not know, but there are means to find out, and when I do, I shall let you all know.

Meanwhile, "Eagle" is said to be of great help in designing circuits. I have put him on the desktop. Doesn't he look fierce?