Topband: Shunt feeding the Skyneedle - new developments BTW-P.S.

[Charlie Cunningham]

By the way, Carl. it sounds like you might have eliminated a bit of series
inductance when you moved the variable capacitor into the enclosure and you
may have picked up a bit of shunt-C by moving it into the metallic
enclosure, but you are so close to "dead-flat" 1:1, that it really doesn't
matter. You could just tweak the variable C to minimize the reactance at the
load, but -j11 is just fine! As I said earlier your 45-j11 resides near the
origin of the chart on a 1.3:1 VSWR circle!

Enjoy and have fun!

73,
Charlie, K4OTV


-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Charlie
Cunningham
Sent: Friday, February 21, 2014 8:30 PM
To: 'Tom W8JI'; 'Carl Braun'; '160'
Subject: Re: Topband: Shunt feeding the Skyneedle - new developments BTW

BTW. Carl

I agree completely with Tom that there's no point in having a static-bleed
choke on a grounded shunt fed tower!

73,
Charlie, K4OTV






-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Tom W8JI
Sent: Friday, February 21, 2014 8:02 PM
To: Carl Braun; '160'
Subject: Re: Topband: Shunt feeding the Skyneedle - new developments

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?>>>>

Any enclosure will change things, especially a metallic enclosure. Just
readjust the cap.

<<<<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.>>>

The choke is completely unnecessary with a shunt feed tower. It won't help a
thing, so leave it out.

73 Tom 

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