My first attempt with a Colpitts oscillator - Criticism requested.

Thread Starter

atferrari

Joined Jan 6, 2004
4,069
I decided to design a Colpitts oscillator with an output frequency of 1,2 MHz followed by a buffer stage. No other specs for the moment.

I would prefer to keep unchanged the coil (I got it salvaged from old radio gear) and the transistors while using a +9V PSU.

Once having it working I would like to be able to adjust (vary) the frequency and increase/decrease the output voltage. How much? No idea.

I am most concerned about the value of C4 and the DC coupling to the buffer but I would be not surprised if I am told that the whole thing is just a piece of garbage.

Prior to starting soldering I would appreciate any comments / suggestions.
 

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Audioguru again

Joined Oct 21, 2019
1,772
None of the many circuits in Google Images shows your circuit. Instead they show the junction of the two capacitors grounded and the collector at one end of the inductor and the base at the other end.
 

Thread Starter

atferrari

Joined Jan 6, 2004
4,069
In fact, AGag, I was "inspired" by a working circuit proposed by a known member in ETO forum. The oscillator is basically the same. The capacitive divider, I found it in several sites.
 

Thread Starter

atferrari

Joined Jan 6, 2004
4,069
Diodes for amplitude limitation.
Here's the diagram, but you'll have to download my library from my web page.
http://bordodynov.ltwiki.org/
Thanks for the .asc file. On to test and see what comes out.

A couple of months ago I downloaded / installed your files but today had to do it again. (¿¿??) Is it that after every update of LTSpice I should do that again? Puzzling. Gracias again.
 

Bordodynov

Joined May 20, 2015
2,646
My collection of models is used by thousands of people. This is the first time I've met your problem. The truth is, I am using Windows 7 and 10.
 

djsfantasi

Joined Apr 11, 2010
6,719
If you install the library in the LTSpice default directory, it will disappear when LTSpice is updated.

Change your preferences to use a different directory. Then after an update, replace the standard filesin your custom directory.
 

Thread Starter

atferrari

Joined Jan 6, 2004
4,069
My collection of models is used by thousands of people. This is the first time I've met your problem. The truth is, I am using Windows 7 and 10.
OK Alex. Win 10 here.

I will keep an eye on this. I was myself, really perplexed when ZZZ disappeared.

Be well.
 

Thread Starter

atferrari

Joined Jan 6, 2004
4,069
If you install the library in the LTSpice default directory, it will disappear when LTSpice is updated.

Change your preferences to use a different directory. Then after an update, replace the standard files in your custom directory.
That means that LTSpice obliterates the content or just adds new sym and sub?
 
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sparky 1

Joined Nov 3, 2018
301
Getting excellent results from BJT Colpitts is not easy. The expectation <4% THD can be compared to Colpitts other than BJT.
An op amp circuit have been known to do that with less messing with extensive parasitic enhancements.
I think you found a troublesome puzzle, probably an embarrassment to some who think it's just a simple fix.
If only I could order that special part, If only that test equipment would tell me the right parameters.
If our expectations not based on the real cause for Colpitts BJT instability a leading cause of Colpitts syndrome.

Ltspice obliterious, startup seems off. I would like to see more instruments to uncover those discrepancies. The waveform is very accurate.

An extensive time consuming study was done. It also is a tedious effort. They all have little errors here and there.
Analysis better than most for 2N3904 Colpitts In table 3.2 using his circuit an adjustable inductor 15uH should get a simulation close.
https://www.arpapress.com/Volumes/Vol16Issue1/IJRRAS_16_1_04.pdf
 
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