I have the following circuit :
It is meant to amplify signals in microvolt range and around 100 MHz. Now in the figure, the transistor is an ideal one. So it works fine and as expected. But as soon as I replace it with actual model, it doesnt work . I need either 2n3904, 2n2222 or bc547. And all three dont work. I tried tinkering around with capacitor values, but no use.
I have seen a few radio receiver schematics for FM ( 88 to 108 MHz). All of them make use of 2n3904 for RF Amplifier ; so it must work for my scenario as well, but it doesnt. (I referred to those Elenco radio kit manuals).
What am I missing ?
More info : Q – point : Vce = 6.3v — Ic = 3.9 mA — Vcc = 12V
Thank you.
Best Answer
You wrote "All of them make use of 2n3904 for RF Amplifier".
But do they use it in the same way?
E.g. you are using a common emitter circuit but they may use e.g. a common base circuit. The maximum frequency both circuits are able to amplify are quite different (i.e. much higher for common base). In your case e.g. the Miller effect might be the problem.