On Mon, 09 Apr 2007 09:12:01 -0700, Roy Lewallen
wrote:

John Passaneau wrote:

I would just use normal 500v silver mica capacitors in series if
necessary. At the 100 watt level the capacitors in a trap don’t have to
work too hard. Silver micas have good RF performance and easy to come by.
If you use EZNEC to model your antenna it can tell you the voltage across
your traps at your max power level making it easy to pick out your
capacitors. You can down load a trial version that can easily model your
antenna.

Keep in mind that EZNEC reports the RMS voltage, while capacitors are
rated for peak voltage. So multiply the EZNEC values by 1.41 to get the
required capacitor rating. Then add whatever additional safety margin
you think is appropriate.

Roy Lewallen, W7EL

Hi All,

I would add that even if this safety factor is ignored (even at the
additional burden of ignoring the RMS to Peak conversion); that some
may feel their set up works fine, but is now off frequency. Mica caps
are said to be "self healing." That is accounted for the removal of
plate area (by the arc through) near the puncture. Net result of
overloading is neither a short nor an open.

You could test them with a Capacitance meter and find they still
exhibit capacitance, and perhaps not much D (but how many meters
actually measure D?).

73's
Richard Clark, KB7QHC