Is this a Clapp AF oscillator in an RF sig gen circuit?

[Radio Wrangler]

Thanks, Peter.

It's a right dog's breakfast. Probably created by empirical bodgery and a little evolution as they kept it. Rather a nasty modulator, but enough to find breaks in signal flow in receivers.

David

[kalee20]

Originally Posted by G0HZU_JMR

I think the key thing to take into account is that the transistor is best considered as a voltage controlled current source for this particular circuit. The voltage isn't inverted (180degrees) at the collector because the load is inductive. If there was only the AF choke there and no feedback the collector voltage would be 90degrees out of phase with the phase of the base voltage when driven with a 400Hz signal.

That's food for thought!

Considered very crudely, from transistor base to transistor collector, there's a phase shift of 90 degrees which is relatively independent of frequency (though the gain will rise steadily with frequency).

For oscillation we need a total of 180 degrees, so the two CR stages must supply the extra 90 degrees. That's 45 degrees each.

The rate of change of phase shift with frequency, for a CR stage, is at its steepest at 45 degrees (at low frequencies it's almost constant at 90 degrees each, and at high frequencies it's almost constant at zero), so it could be said that this circuit has its frequency determined by the CR values, and moreover it's a bit more stable than the 'traditional' 3-stage CR phase-shift oscillator where each stage has to contribute about 60 degrees.

All the above is very crude, it completely ignores the loading effect of any CR stage on the one before (or on the inductor), so it is highly approximate.

[6SN7WGTB]

I hope this isn’t a silly question but why is a Wien Oscillator not used in this sort of application?

[kalee20]

Because it needs a non-inverting amplifier? So, two transistors are needed. And at the time, they were more expensive than the odd transformer.

[Radio Wrangler]

The Wien bridge oscillator also relies on better level control, usually by a thermistor, and the fast acting bead in an evacuated bulb type were dearer than transistors.

David

[Skywave]

Originally Posted by G0HZU_JMR

What is ELI the ICE man?
ELI the ICE man is used to remember the relationship between current and voltage in an inductor and capacitor.

I've always used CIVIL; (I find that a much easier mnemonic to remember.)
C = capacitance; L = inductance; V = voltage; I = current.
Study the sequence of the letters: For C, I is before V. If I comes after V, then L.
Thus for C, I leads V; for L, I lags V, therefore V leads I.
(First met 'CIVIL' when studying for ONC Electrical Eng.at college in 1968; have been using it ever since.)

Al.

[G0HZU_JMR]

Good one, thanks! It's the first time I've heard of the CIVIL alternative.

I agree CIVIL is much easier to remember and much easier to work with.

[Skywave]

Looking at the rate of posts made to this thread, seems that it is reaching its end. So before it does, just a few concluding remarks relevant to my previous post.

[QUOTE=G0HZU_JMR;1428031
I agree CIVIL is much easier to remember and much easier to work with.
[/QUOTE]

Jeremy: I'm pleased that you found that post of mine of value. Your response was indeed more that just civil.
On the odd occasion when I feel I can make a positive contribution to a thread, I like to do so, even if that post gets close to being off-topic.
'Nuff said!

Al. / Nov. 30th.