Topband: Shunt feeding the Skyneedle - new developments

[Charlie Cunningham]

Exactly!  All true and Tom is right on point!  You have removed a lot of
series reactance with that "gamma cage", Carl -as  indicated by the required
tuning C changing.from 160 pF ot over 400 pF. OF COURSE the Q was reduced as
the series reactance was reduced and the real part stayed fairly constant.
That does not imply increased or excessive loss!

Regards
Charlie

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Tom W8JI
Sent: Saturday, February 22, 2014 9:07 PM
To: Carl Braun; '160'
Subject: Re: Topband: Shunt feeding the Skyneedle - new developments

I was pretty satisfied with this scenario so I mounted my variable cap on a 
3/4" thick piece of Plexiglas to the backplane via Teflon bolts inside the 
steel enclosure.  When I did this I saw my analyzer jump to 45 -j11 ohms. 
No matter how much tweaking was done the lowest "X" on the analyzer was 11. 
Figuring I could live with that after making 24 contacts this morning I 
decided to move ahead with my gamma cage.  When I completed the cage per the

info above I left my analyzer set on the previous frequency setting of 1825 
and saw the resistance jump and the X go out of site.  Adjusting my variable

cap (from approx 140 pf to 420 pf) rewarded me with a 42 + j0 reading.

Inside the shack on the 1000D and the BIRD I see 1.1:1 Vswr at 1.800 MHz, 
FLAT 1.0:1 from 1.810 to 1.860 and 1.5:1 at 1.895 MHz.>>>

I would expect you to have that bandwidth. It does NOT indicate loss.

Your shunt system now has an operating Q of around 4, because you now have 
200 ohms of series C.

With a thick radiator and a large yagi on top, and so much capacitance, you 
are exactly on target.

While I don't fully trust the FT1000 meter, no matter what, never 
automatically assume modest bandwidth like you have indicates loss. It 
doesn't. There are a whole lot of things that go into bandwidth beside loss!

73 Tom 

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