Topband: Shunt feeding the Skyneedle - new developments

[Charlie Cunningham]

Well, Carl

I plotted your 45-j11 load on a Smith Chart (normalized to 50 ohms) and it's
very near the origin on a 1.3:1 VSWR circle. Since you have a relatively
short feedline of LMR-400, You should be able to just tune it out at the
transmitter end of the line, and the LMR-400 line will be operating at such
a very low SWR (around 1.3:1 that the excess loss from a 1.3:1 VSWR at 160
is completely trivial and negligible! It may not be completely
"intellectually satisfying to have -j11 of reactance at the load, but it
should match easily and the antenna should work very well!  Enjoy!

Sounds like that Array solutions static bleed is not as high in impedance as
we might wish! A large resistance might give you more satisfactory results!

GL!  Enjoy!

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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