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@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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