As any semi-nerd-academic I started by buying the books, I bought the ARRL Handbook, the then I read a blog referencing to EMRFD. I must admit that RF always sounded difficult, complicated and away of normal engineering. Like a cult or a secret society. No information was ever revealed.... Finding a book having "Experimental" on the title caught my attention and showed me it was probably not the reality.
By the way, I have no plans to become a HAM, I just want to try and learn RF. Because of that I have to use the ISM bands available (and within reasonable power less than 2W, radiated probably less than 0.1W).
I'm still reading (in the engineering way) both books, but after some reading I decided it was time to build something.
Having worked in power electronics (and in the light of my new "interest") I decided to build something I knew was used both in RF and induction heating, a class E amplifier/driver but I had no personal experience.
Class E was defined by the N. and A. Sokal in 1975 with a US patent 3'919'656
(Nov 11, 1975) and in 2001 new refined design equations were presented in QEX Jan/Feb 2001 (also by N. Sokal).
My requirements are simple to start with output power 1W, a 5V supply, a Vswsat 1V, operating frequency 6.78MHz (ISM band and I also have a Short Wave receiver that receives this frequency), Qload 6. This is all you need, if you use the 2001 formulas determining L1 will be iterative (the 1975 formulas should be OK and are not iterative).
Having seen a few pages (here, here and here) using the 2N7000 and having tons of them, I decided to use it in the project.
Being a bit academic I calculated the values, substituted the NMOS with a voltage controlled switch and simulated the circuit.
|Schematic for simulation of a Class E Amp|
|Voltage and Current in the Class E Amp|
In the picture above v(500) is the switch voltage, v500#branch is the switch current and the v(900) (sinusoid) is the load voltage. The power in the switch was also relatively low with an average below 1W (V500 is a 1V source to simulate a voltage drop in the switch). This without tuning the circuit (but also without a real 2N7000).
|Power through the Switch|