Johan and LF,

During my experiments with class E the choke was not a component to which I
paid great attention.  Having said that, when operating at 500khz, I tried
reducing the value to around a few 100uH which resulted in instability.
Increased to 4mH at which value the amplifier operated perfectly.  That's
where I left it and tolerate the very small increase in voltage drop. The
amplifier operates at 90% or better efficiency when run at the design values
As an aside, I have not blown a fet when running into open circuit or mis
tuned antenna.
Thanks for the info Johan

73

Mike GW4HXO.
 -----------------------------------------------------------

Subject: LF: Smaller DC feeding choke in class E amplifier

LFers,

the usual design equations for class E amplifiers assume that the DC feeding

choke has a very large inductance in order to keep the DC current
practically 
constant over the RF cycle. I am in the process of building (yet another)
class 
E CW QRP transmitter and the need for an almost infinite inductance has
annoyed 
me for quite a while. Somewhere between the solder smoke puffs, I did some 
googling and found this interesting paper:

   http://www.msm.ele.tue.nl/~dmilosev/ECCTD2005.pdf

My current project is a small 80m TX but I think this information is
applicable 
to LF as well.

73
Johan SM6LKM


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