Topband: Shunt feeding the Skyneedle - new developments

Carl Braun Carl.Braun at lairdtech.com
Fri Feb 21 19:32:11 EST 2014


All


Topband list

If you've followed my efforts to shunt feed my Skyneedle tower you'll know that I settled with a tap point of 67' and 30" or so of spacing with my feed point reading 42 + j0 ohms.  This reading was taken at the interior of my 20 x 30 x 8" steel Hoffman enclosure with the variable cap located outside the enclosure sitting on a plastic 5 gal jug.  The output of the variable cap fed into a ceramic feed thru insulator thru the panel to a copper "L" bracket that mounts the SO 239 connector that I hooked my coax cable to.

Since then I've moved the variable capacitor inside the panel and mounted it to a ¾" think Plexiglas sheet mounted to the back plane with nylon bolts and washers.  There is a 1" air gap between the Plexiglas and the backplane.  I now have seen the 42+j0 ohms change to 45 - j11 ohms...that's the lowest reactance I can tune the capacitor for. Not really sure if its +j11 ohms or - j11 ohms but I assume if the reading was + j11 I could continue to tune it out with the capacitor but I cant.

Does the capacitor not play well with a steel enclosure?

The other strange situation I'm experiencing is when I connect my Array Solutions static bleed choke to the feed thru insulator at the outside of the panel to ground the resonant frequency jumps to 2.014 MHz at 25 +j0 ohms...remove it entirely and I'm back to my 45 - j11 ohms.

I use 1 meg ohm from the feed point to ground on my other verticals with NO change in MFJ analyzer readings.

Any comments from the list on these problems?

Thanks


Carl AG6X



More information about the Topband mailing list