[Amps] Class E amp (was FCC Denies Expert Linears' Request for Waiver of 15 dBRule)

[Manfred Mornhinweg]

Hi Peter,

> A friend of mine, ex Telefunken design engineer, already built a class E amp
> around 2x8 cheap SIHP10N40D transistors at less then 1 Euro each.
> With 15W of drive output is 1200W.

I just had a look at the data sheet of that FET. Judging from the specs, 
I would think that it's usable on 80 and 40 meters, but problematic on 
20, and not usable on 10. Do you know what bands that amplifier actually 
covers?

> Even without predistortion IMD3 is less then -30dB.

Class E showing good linearity, without using predistortion? That has to 
be an EER design, which is not what I intended to do. Even in an EER 
amplifier, it's problematic getting good linearity with MOSFETs having 
capacitances as high as these! That was what put an (at least temporary) 
stop to my own EER work.

I would really like to see the schematic of that amplifier, and actual 
test data. Is this available somewhere?

> 20 transistors will do your legal limit easily.

Yes, that should indeed be possible. But I would use transistors that 
have lower capacitances. People often think that high output capacitance 
isn't a problem in class E, but there is a limit to this... The problem 
is that the output capacitance is so very voltage-variable. And Crss 
limits the gain, causes drive power feedthrough in class E amps, and of 
course is also voltage-variable. The voltage-variable capacitances cause 
phase distortion. And even the input capacitance is a problem, when it's 
500pF like in that transistor. With 20 of those, you need either a tuned 
input circuit (bandswitched), or heavy resistive loading (which 
drastically lowers the gain).

It would be great if you could let us know where to get more information 
about that amplifier!


Manfred


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