I've calculated out a class C amplifier while working with RF Power Amplifiers 2nd Ed. by Marian Kazimierczuk and the Spice model works of my design works wonderfully, but when I build up the circuit I get a large amount of current draw ~100-200 mA but hardly any output at all.
I notice maybe a ~10-20mA increase in power draw when connecting my 4.7Ohm load. The Xc of the capacitor I'm using is ~2Ohms at 7.2MHz so it's not the coupling cap. I must be doing something wrong.
I do realize that for the sake of clarity I'm going to point out that this is on a breadboard, but even if I adjust the frequency down a lot and redesign for ~1MHz I still get a problem with coupling of powers. Whenever I try to design an amplifier I always end up with funky coupling problems like this and I have no idea why since this design even has the matching network.
I'm using a function generator to bias the transistor with a DC offset on top of the signal, which is the only thing I've been able to come up with as an issue, as maybe it needs significant amounts of bias current but I thought this should be fine since I'm using an IRF510 MOSFET.
ElectroTactical, you have a link to some picture or other (schematic ?), my system refuses to display that link, can you please copy the picture/schematic/?? directly to the forum please?
Use the Upload a File button at the bottom right hand corner of the page.
If I read the values correctly, L1 is 411nH, which gives an Xl of about 18 Ohms.
This is a bit low, if you want a load impedance of 4.7Ohm, make L1 have a reactance at least 47 Ohm.
What is that parallel tuned circuit doing?
I calculate that it has a resonant frequency of about 19.7 MHz.
As a general comment, you have no decoupling capacitors on the 12v supply to the MOSFET.