colpitts 2

[yacine]

hi, please I want to know how to calulate the capacity that found between the coil and trans of transistor in colpitts oscillator much time that oscillator used in fm transmitter take look at this link
**broken link removed**
I designed one oscillator and I make an cpacity between coil and trans of transistor to works like feedback by resestance of coil
do it will works ?
all objectives by this Idea is building an RF receive
greeting

 

[RadioRon]

I do not understand your request. When you say "trans" of the transistor, do you mean the collector or the base or the emitter?

The capacitor connected in parallel with the coil is estimated using the equation

Frequency of oscillation (Hz) = 1/(2 x pi x sqrt(L x C))

where L is inductance (H) and C is the parallel capacitor (F). This is only an estimate because it ignores the small contribution from the antenna and from the collector-emitter capacitance and from the collector base capacitance. I think the value of L is about 0.5 uH.

I'm not sure but I think the feedback capacitor from collector to emitter is chosen to provide a reactance of about two to four times the emitter resistor value at the frequency of oscillation. This cap, along with the emitter resistor and the resonant impedance of the tank circuit forms a voltage divider that determines how much feedback is fed from collector to emitter. I think a lot of builders tune this value on the bench to optimize the circuit.

I still don't think either of these circuits is a Colpitts, but whatever.

 

[Hero999]

They're both the same circuit but with different component values.
**broken link removed**

I don't know what sort of oscillator they are either but they aren't colpits oscillators.

I don't know the name of this oscillator circuit, I haven't seen it in any of the text books, I've only seen it on the Internet.

I've discussed this in another thread, I prefer to call it a common base oscillator.

 

[yacine]

re colpitts

hi, thank you for your reply I mean by the word trans is emitter and and my last thread about cpacity between collector and emitter
I have another schematic personal design but I do not know if it will works or not (Attached schematic)
please, can it replaces a last oscillator ?