[Milsurplus] Ant. Series Matching Caps- I Just Don't Get It.

[David Stinson]

Over a year ago, I was trying different kinds of series caps
to match the 5-to-12 Ohm outputs of WWII aircraft rigs
to our 50-Ohm standard.
I tried several things and discovered that a lot of caps would
eat-up power.  We talked about it.  Folks said they wouldn't
handle the RF current and indeed, some of them heated and
I saw lower power out.  We discussed how "100 pFd wasn't
always 100 pFd," depending on the cap type.
I eventually settled on using RF "doorknob" caps as being best.

This evening after work,  I decided to go through several kinds
of caps and record just what was best/worst etc.
Remember how some of us have puzzled over how we can
make a test one day, get a certain result, then days or weeks or
years later, do it exactly the same way and get radically 
different
results?  I know-- sounds crazy, but....

Tonight I tested all these caps on the output of the BC-230
on 7029 KC and also a good-quality air variable.
http://home.netcom.com/~arc5/SCR-183/Justcaps.jpg
They all run between 50 and 68 pFd.
The ceramics were NPO and N750.
 The little mica is just a mica- nothing special.

With the exception of the red "high voltage" cap, which did
indeed introduce loss and chirp,  all these caps performed
nearly indentically.
The NPOs did seem a little more stable but that might be
my imagination, too.  Wasn't much difference.
The air variable did no better than the little 68 puff N750.

I don't understand it.  How can two sets of basicly identical 
tests
a year and change apart produce such radically different 
results??
I'm starting to believe in gremlins and magic "spooks"
in our radios.  I don't know what else to think.

The only thing I can suggest when you go to match the output
of your WWII transmitter is to try several cap types.
Find the one with least loss and that doesn't introduce any 
chirp.

No wonder my hair is all falling out....

73 DE Dave AB5S