[ARC5] Ant. Series Matching Caps- I Just Don't Get It.

[Jim Falls]

This is how I match audio output transformers to whatever rig they're in.

Same with diodes used in my crystal sets. 

Math will only get you so far, then individual manufacturing issues negate all that number crunching. 


Cheers!
Jim K6FWT
CBLA #37

> On Jan 14, 2015, at 19:04, David Stinson <arc5 at ix.netcom.com> wrote:
> 
> 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
> 
> 
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