Date: Wed, 21 Nov 2007 14:43:08 +0000
From: John GM4SLV <gm4slv@sighthound.demon.co.uk>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: CLASS E
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On Wed, 21 Nov 2007 12:20:17 -0000
"hamilton mal" <g3kev.ham@virgin.net> wrote:

> You were a late starter on 500. I would say you have missed a lot.
> G3KEV
> 
>


Undoubtedly I was and certainly I have. 


Your snide comments aside, I'm referring to your recent reported
measurements and optimisation of tuning components to achieve good
drain waveform as recounted by you on 18th November. It was a very
interesting report, showing what can be done by observing the waveform
to determine the necessary adjustments to tuning and loading on these
amplifiers.


I assume that after all the painstaking work to select the correct
values of capacitor to get the optimal drain waveform that you measured
the efficiency? 


If you've previously posted such results, prior to June 2007 when I
joined the LF reflector, then I will certainly have missed them, but
then your earlier data is not relevent to the recent reported study. 

I simply asked if you could fill us in with the important details of
power input/output and efficiency (which surely is the point of using
these Class-E amplifiers) which your report (copied below) seems to
lack.


Regards

John



Hi all
I carried out some analysis on my fet pa today to check the waveform for
true class E. Monitoring the drain on a scope revealed that the
waveform was almost correct but needed a slight increase in capacity
for C2 for an almost perfect switch at 502.5 khz. Increasing/decreasing
the voltage did not make a big difference to the waveform, at the
design voltage it was only slightly better.
Using a DL I altered the freq and found the perfect waveform at 535.9
khz, so I expect logically increasing the value of C2 would correct the
anamoly at 502.5 khz. I have not altered it yet because I do not have a
suitable capicator.
I did observe some ripple on the waveform that is probably caused by
feed through from the driver, it was more pronunced at a V lower than
the design voltage, but improved with a V increase.
In spite of the above observations the PA performs well and seems very
robust.
The RF pwr out  measurements using the DL or the Antenna do not vary,
indicating that the antenna is well matched to 50 ohms via the atu at
the base of the inv L.
I thought the above observations might be interesting to would be class
E constructors.
Considering mine was built from junk box bits, including the 60 year old
ceramic ex TU5 tuning unit coil  it works very well. The fet is out of
an old marine tx.