Harros said:
Is the RF choke the ferrite bead? By the way, i dont really know the correct method to design class C amp, as i never touched this type of amps before. Well, do you have any idea on the determining the value of the components (inductor, rf choke, and capacitors) used in the amp?
Besides, I can hardly get a exact ferrite bead at my place for the particular ferrite bead used in the simulator, and I am thinking of editing the PSpice model of the ferrite bead... Do you have any idea on the corresponding values defined in the PSpice model of the ferrite bead?
An RF Choke is an inductor (whose Q is not considered important or is sometimes intentionally lowered) with an inductance that presents an impedance to the circuit that encourages RF power to flow somewhere else. In other words, when used in a circuit, a very low amount of RF current flows through the choke when compared to the other directions that RF current can possibly go.
Chokes are usually used to provide bias to an RF circuit. You can imagine that in the same way that a capacitor is useful for blocking DC and coupling AC into a circuit, the choke is useful for blocking AC and coupling DC into a circuit.
Now, in your case your desired RF signal is at 1 MHz. To be a useful choke in your circuit, you have to estimate the input impedance of the base of the transistor and then set the inductance of the choke to be at least five times higher than that. This is quite difficult to do, so we will just guess that you will be inputting an average current of about 1 mA into the base with a voltage of about 0.7 volts, so our guess is 700 ohms. So, you need a choke that is about 3500 ohms of inductive reactance. That's quite a lot and there is no way a ferrite bead will get you anywhere near that. Such a choke will involve many (hundreds?) turns of fine wire on a ferrite core.
For the component values, I suggest that you leave the collector load of your existing 2n2222 amplifier circuit as it is, perhaps reduce the emitter resistor a little bit, and then change the base bias to be only the choke to ground. All you are doing is taking your other amplifier and reducing the base bias to zero. Of course, this means that your collector bias current is also zero, but otherwise the resonant tank values can remain as they are.
Edit: If you can't find a choke inductor, go ahead and try it with a resistor to ground from the base instead of an inductor. Perhaps a value of 1K ohms for starters.