[Milsurplus] Smart People: Where'd the Harmonic Come From?

[David Stinson]

Working on the BC-230 transmitter tube
substitution project, ver. 2.0

To match the output of the transmitter to my
50-Ohm non-reactive load,  I've inserted a 100 pFd
"doorknob" in series with the dummy load.

http://home.netcom.com/~arc5/SCR-183/BC230TX.jpg

Scoping the output of the transmitter, before the
100 pFd cap, we see a nice, clean 500V PTP
waveform.  Image003 attached.

Scoping the output side of the matching cap, going
into the dummy load, the waveform is 55V PTP with
25V of 2nd harmonic.  Image001 attached.

First I thought of some non-linearity in the
matching cap, but this happens with every cap
including a high-quality variable.  I did not try
another 50-ohm dummy load.
However, using the original-recommended dummyload
of 100 pFd in series with 5 Ohms
displayed a clean waveform of about 700 V PTP,
with only a minor difference in
the Ant Tuning control between the 100-pFd-5-Ohm
load and the 100 pFd-50-Ohm load.

Has anyone an idea of where/why this harmonic
energy?
Is it possible my 50-ohm "Mighty Fine Junk"
dummyload has the non-linearity?

TNX OM DE Dave AB5S

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