On Sun, 06 Jun 2004 17:59:00 -0500, Ed Bailen wrote:

The last issue of QST had a short article on the CircuitMaker Student
edition circuit design package. I downloaded it and spent several
hours trying various oscillator designs (including the phase shift
oscillator discussed in the same issue of QST). I couldn't get any of
the designs to oscillate! I was mainly trying Colpitts oscillators.

Typically, an oscillator is just a noise amplifier with some frequency
selective feedback. In a real oscillator, there is always some wide
band thermal noise present, which is amplified, some selected
frequencies are circulated back to the input and reamplified and so
on. Finally, there is going to be a narrow spectral line and a wide
band noise floor due to the thermal noise, assuming of course that the
phase, amplification and feedback loss conditions are correct.

If the simulator does not simulate the thermal noise inherent in all
resistors and semiconductors in temperatures above absolute zero, it
is not very likely that the design would oscillate. Inject a very low
level wide band noise into the amplifying stage and the oscillation
should start. However, I have never seen the CircuitMaker or how to
generate a wide band noise signal with it.

Paul OH3LWR