2 transistor Butler Oscillators
Name is Kevin, ZL1UJG. New to the reflector and new to SDR.
I have used the 2 transistor Butler oscillator many times.
(VHF/UHF/microwave) What can occur when the transistors have more than
sufficient loop gain, during the RF cycle, is that they are partially
cut off. This can be measured by looking at the Vbe of the transistors
in the oscillator.(using a DVM isolated with a 10k resistor and
measuring Vbase and then Vemitter of the transistors) With some modern
SMD devices I have measured 0.15V Vbe. I have not got any of the kits
mentioned on the reflector yet, so cannot measure what these units are
like. Adding clamp diodes across the tuned circuit (such as 1N4148)
typically brings the Vbe back to a suitable range.
Another point with oscillators is the effect that PSU noise has on
phase noise. (78 and 317 type regulators can increase the composite
phase and amplitude noise (especially seen when the frequency is
The Wenzel site (www.wenzel.com) has active PSU filter designs which
can be added to the output of the regulators to reduce the noise.