Hi all
I have a problem with colpitts oscillator
I have a circuit (I uploaded it).
so I use 4700p caps and various amounts of inductor my transistor is 2SC3355 not on spice
Problem is that when I remove inductor ,like second schematic I get oscillation about 200Khz .
I calculated and I get that I must have 270uH inductance for this oscillation but where is that ?
also when I replace inductor like 56u I get higher frequency but what is my total inductance ?
Please help me I get confused .

 

The feed back is determined by the ratio of C1 to C2. That is the most critical aspect of the Colpitts oscillator, with respect to starting, and stability.

 

The feed back is determined by the ratio of C1 to C2. That is the most critical aspect of the Colpitts oscillator, with respect to starting, and stability.

Hi
Yes but why that oscillation I mentioned above occurs ?

 

Hello
I just want to say that I tested my circuit on pcb instead of bread board and I get the true results
But I do not get the answer "Why on breadboard it oscillates on 200Khz ? "

 

Solderless breadboards have a lot of parasitic capacitance and tend to result in circuits with a lot of parasitic inductance, as well.

 

Solderless breadboards have a lot of parasitic capacitance and tend to result in circuits with a lot of parasitic inductance, as well.

Yes of course but 270uh is not a little large value for breadboard inductance ?

 

Hi
With values : c1=4700n c2=2200n and l=74u
I get the result below
Why the result is not sinusoid ?