Oscillator

[yasir_ali]

Hey contau! what is the concept of this RFC(Radio Frequency Choke).? why we use it instead of RC?

 

[contau]

RFC is the inductor which has high reactange prevent the high frequency affect to supply power and it also improves Q factor of oscilator circuits. if the oscilator without RFC, it will be small Q and oscilation will be not stability

 

[yasir_ali]

so how to use it? as i told you that i have never use.


thanks

 

[burhanmz]

@sorry yasir i got busy.
when you are practically implementing your colpitts oscillator, use wire wound inductances and not the (resistor type color coded ones), or if you are a student of some university wire wound your own inductor and ask your lab staff to let you use their LC meter and measure the inductance.

although colpitts should be used only for high frequencies, but if you still want to design an oscillator in 10s of khz then only use single wound inductors (they'll get pretty large and bulky)

i think more or less everything has been answered here.
here are a few pointers

the product of attenuation (B) of feedback (capacitive of tank) and amplifier gain(Av) should never exceed 1.2 to 2 (in fact keep it near 1.4 too much will distort the start up of oscillation which might end up in no oscillations at all)

start up condition > Av . B

where B = C2/C1 (C2 being the collector side capacitor)
keep B in between (5 to 20) any more and oscillations will take minutes and hours to build up or not at all

use C1 and C2 small disc type caps. their values can be as low as 1nF to as high as 100nF (0.1uF)
thats all

My question to this thread is why resistor type color coded inductors are poor to sustain oscillations or get any oscillations at all?

 

[yasir_ali]

@ burhanmz
I am not in any university or college. I felt this subject very interesting, i found myself very interested in it.That's why i started learning Electronics.And it is really interesting subject. And your points, what you told above, are really helping. Thanks a lot.And if you see above i have successfully designed my own colpitts Oscillator.in post#35, i have shown my oscillator.that is working at 1MHz.The Sine wave in my oscillator is not so well but i know what is the problem with it and can correct it.Now, i want to construct it.But i have stuck on INDUCTOR. i am reading the theory, that how an inductor react with A.C signal and let D.c go through itself without any problem. but i am still unable to construct one for my Oscillator.so can you help me understanding the way to construct an Inductor?

thanks

 

[burhanmz]

here is a very nice link to do that..

Coil Inductance Calculator - 66pacific.com


and if you are more interested in electronics then this would really make you happy

Very Accurate LC Meter based on PIC16F84A

 

[yasir_ali]

@ burhanmz
Hey! your links are great specially second one. actually, as i told you before that i very new to Electronics. i don't these Ics. but i just know a little bit about these programmable Ics. i would love to make it but the problem occur to me will be the program is not available for PIC16F84A. and second problem is, if i get program it will very hard for me to put program into this Ic because the device put the program into Ic is very hard to get. and if i get its very expensive.