Topband: Shunt feeding the Skyneedle - new developments

[Carl Braun]

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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