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How to build a simple LC oscillator

A

Alexis Bezverkhyy

Jan 1, 1970
0
Hello !

I'm new to analog electronics (although I've been using uCs for a while)
and I'm trying to build a really simple RC oscillator, a Hartley or a
Colpitts one. All the schematics I've found on the web or in books are
using complex and additionnal components (like 4 pins MOSFETS, JFETS,
transformers...). The two or three models that I've tried to build
weren't oscillating at all. I want to keep it simple to be able to fully
understand what's happening (otherwise I'd have used somme xtal or IC).

Do you know some simple LC oscillator schematics using standard
components that would simply oscillate at few MHz ?

Thanks
 
J

Joerg

Jan 1, 1970
0
Alexis said:
Hello !

I'm new to analog electronics (although I've been using uCs for a while)
and I'm trying to build a really simple RC oscillator, a Hartley or a
Colpitts one. All the schematics I've found on the web or in books are
using complex and additionnal components (like 4 pins MOSFETS, JFETS,
transformers...). The two or three models that I've tried to build
weren't oscillating at all. I want to keep it simple to be able to fully
understand what's happening (otherwise I'd have used somme xtal or IC).

Do you know some simple LC oscillator schematics using standard
components that would simply oscillate at few MHz ?

A phase shift oscillator using a regular low-cost transistor? Figure 2
shows it:

http://www.uoguelph.ca/~antoon/tutorial/xtor/xtor7/xtor7.html
 
J

Jamie

Jan 1, 1970
0
Alexis said:
Hello !

I'm new to analog electronics (although I've been using uCs for a while)
and I'm trying to build a really simple RC oscillator, a Hartley or a
Colpitts one. All the schematics I've found on the web or in books are
using complex and additionnal components (like 4 pins MOSFETS, JFETS,
transformers...). The two or three models that I've tried to build
weren't oscillating at all. I want to keep it simple to be able to fully
understand what's happening (otherwise I'd have used somme xtal or IC).

Do you know some simple LC oscillator schematics using standard
components that would simply oscillate at few MHz ?

Thanks
If you want a simple OSC and make your own coil, look at a
Armstrong Oscillator.

That has what is called a tickler coil, another coil is wound
on the same form as the feed back etc..
We use a armstrong variant osc that generates 100Khz at 250 K watts.
It's all one tube!, Very simple.

http://webpages.charter.net/jamie_5"
 
A

Alexis Bezverkhyy

Jan 1, 1970
0
Joerg a écrit :
A phase shift oscillator using a regular low-cost transistor? Figure 2
shows it:

http://www.uoguelph.ca/~antoon/tutorial/xtor/xtor7/xtor7.html

I've just succeeded in building the phase-shift oscillator (fig. 2).
I did it with a 2N2222 which seems to be almost the same as 2N3904, but
the setting of R6 was quite subtle to make the circuit oscillate.
I could finally probe the RC network with a scope and understand how it
works !

I'll try John's circuit tomorrow.

AB
 
J

Joerg

Jan 1, 1970
0
Alexis said:
Joerg a écrit :

I've just succeeded in building the phase-shift oscillator (fig. 2).
I did it with a 2N2222 which seems to be almost the same as 2N3904, but
the setting of R6 was quite subtle to make the circuit oscillate.
I could finally probe the RC network with a scope and understand how it
works !

I'll try John's circuit tomorrow.

The hfe for the 2222 is quite poor at low currents, see if you have some
small signal BC-type in your junk box. Those are more popular in Europe.

Hey, but at least it worked.
 
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