Topband: Shunt feed series capacitor

Earl W Cunningham k6se at
Sat Jan 15 15:27:13 EST 2005

Jorge, EA2LU wrote:

"Results: 1:1 SWR at 1870Mhz with full caps As you can see I need some
more capacity, like Earl advice.  Question; I have very good quality
500Pf vacumm cap, but it need some more capacity, to put the antenna on
QRG. ¿Could I add 100Pf  fixed from 100Pf 15Kv doorknow capacitor from my
"junk box"?"
If you have 1:1 SWR at 1870 kHz, that means you should put the shunt wire
tap a little higher on the tower to bring the frequency down to 1830 kHz.
 I suggest that you move the tap from 25 feet (7.62m) up to about 26 feet
(7.93m) with the same spacing and still use the 500 pF capacitor.

Another way to bring the frequency down is to increase the shunt wire
spacing from the tower.

Yes, you can parallel the 100 pF capacitor with the 500 pf, but if 1870
kHz is the point of 1:1 SWR, that means the tap height must be higer or
wider spacing.

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