[600MRG] Tuning my transmitter

[Steve Flood]

I am using the GW3UEP 100w transmitter circuit.  I have two IRF540's in
parallel.

I am attempting to optimize my transmitter efficiency while learning
something about FET operation and Class E behavior.

 

In much of what I've been reading, tuning and optimization is done while
monitoring drain voltage and drain current, with the idea that one of these
must be zero when the other is non-zero or "on".  However, I do not have a
current probe for my oscilloscope, nor do I intend to buy one for $1700
(Rigol).   By only looking at drain voltage, I've only made minor
adjustments to the tank circuit to make the waveform look as clean as
possible.

 

With my power input at 86 watts (24v @ 3.6A),  I get 64 watts out to a dummy
load, or 74% efficiency.  GW3UEP specifies 80% and the general class E
literature cite efficiencies in excess of 90% (such as Sokal's 2001 QEX
article).

 

Without a current probe to measure drain current, how are others
tuning/optimizing such circuits?

 

Thanks,

Steve KK7UV/WH2XNV

 



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