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[Towertalk] Advice pse--Shunt Fed Tower on 80m (or 160m)

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Subject: [Towertalk] Advice pse--Shunt Fed Tower on 80m (or 160m)
From: (Mike & Coreen Smith)
Date: Wed, 31 Jul 2002 20:33:05 -0300
Hi Bob/K3UL !! (and groups)
Long time no hear Bob(on 6 or 160, hi hi!!)

Hope your shunt-fed tower is working out for you.  Your country totals are
amazing !
To everyone: (you too Bob ;-)

I just shunt-fed my tower on 80m, but it's not working "right".
I think my tower is resonant somewhere around 2.6MHz (give or take), but
I'll be daRned if I can
get it to load with a nice low/sharp SWR curve on 80m or 160m.  I'd prefer
to get it on 80m as my Inverted L on 160m works nicely.
<<80m -*and*- 160m would be a bonus>>
Someone mentioned that they thought you guys could give me some advice as to
how to do it correctly. (yes I have searched the web and TT archives, but
I'm not finding exactly what I need (not yet anyway).

I am in the process of kinda temporarily (for 1-2 yrs) rebuilding a lot my
antennas as most of the whole farm was dismantled earlier this year (long

I can get the towers' SWR FLAT @ 2.6Mhz (MFJ ant. analyzer) @ various cap
settings, gamma tap points, spacings and even pulling the gamma wire out
like a delta feed.  I can 'also', (using diff settings) get a very broad SWR
curve which is lowest and around 2.1:1 centered on 3.5MHz which is what I am
using now, but I really don't think the tower is working "well" as some 80m
signals are louder on my 160m inverted L. (especially as I go up the band
towards the SSB portion)

For info, it's a 48' Delhi self supporting tower in 3.5 cu yds of concrete,
VG moist to wet soil,
The tower has a TH6DXX on top, right @ the thrust bearing.  Up the mast ~12'
there is a CC D40 Dipole, ~4' above that there is a
~23' boom 5el 6m yagi and on the VERY top there is a Ringo Ranger 2m
Vertical. There is a picture of it at:
The wires and dipoles you see in the photo are no longer there. The 3el 6m
side mounted beam is also no longer there.
The 2 small vertical ropes that are about 1' away from the mast ARE still
there but are non conductive and do not affect
any of the antennas.  I was going to add inverted vees or dipoles for the
WARC bands but never got around to it.

I've tried tap points @ 12', 20', 30' and currently around 35'. Tried
spacings @ 1', 2' and 3' away from the tower.
Gamma wire is #14 AWG stranded/insulated. R90 or TWU I think.
Little difference (believe it or not) no matter what combination of
"settings" I used.  It just seemed to make the SWR curve
broader the less capacitance in line, however the broader the curve got, the
higher the SWR was too.
My only cap is an ~800pF air variable.  Shield of coax connected to lots of
127' radials. (field common to my 160m inverted L -  30' away)
I don't (currently) have another cap for an Omega Match.
*******Q U E S T I O N S************
Do I need to go to the top of the tower with my gamma wire? (I hate climbing
Will grounding the shield of the coax at the tower base make ANY difference?
(just conn to radials now)
Do I need to go further than 3' or closer than 1' to my tower for the gamma
What band(s) will this brute load on?
Do I need to scrap the whole idea and just toss my 60-70' of wire over the
nearest fir tree and be done with it? ;-)

50 or 60 trips either up the tower or outside to tweak the cap or move the
angle of gamma wire and I
and just about ready to fling the 80m inverted L wire over the nearest tree,
like I had before.....

THANKS!! :-)

73 de Mike

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