Re: Output vs. frequency behavior QCX 30m
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Hi Bill. C30 and L4 ARE important for good operation of a class E amp as
you want losses to be minimum here. Take a look at pages 112 and 113 in the QCX
manual, and the referred articles, which go into detail about the class E
stage.? Pure L-C calculations don’t quite work because the output
capacitance of the FETs is part of the tuned circuit. Hans says on those pages,
“A Class E Power Amplifier contains a
resonant circuit at the frequency of operation, so
it is only suitable for single band use.” From the
little I know but have read about concerning class E amplifiers, most will
operate very efficiently only across a? portion of most bands, 40 and 20
meters included.? The cap value really needs to be optimized around the
frequency of interest for best
efficiency
?
-Steve K1RF
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Sent: Wednesday, December 13, 2017 12:22 PM
Subject: Re: [QRPLabs] Output vs. frequency behavior QCX
30m
?
Steve
K1RF,
How critical is the resonant circuit C30 and L4 for single band
performance?? Are we looking at a broad bell shaped curve response or a
sharp peak?? I think I read somewhere Hans picked the values by experiment
because of the "floating" capacitance from the FETS etc.? Maybe a mica
capacitor would be in order for C30 if the original were heating up.
Bill
N7EU
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