[Towertalk] 80m shunt feed -DESCRIPTION

[Mike & Coreen Smith]

Pardon  those that know this stuff back and forth, but I've had 5 or 6
requests to tell people what Ive done to
load my tower on 80m.  This is old hat to most here <I know>, but there
seems to be an email coming in every half hour
asking me to explain, so as not to bore anyone I'll try to keep it short.
Please, guys, any technical questions re: this particular setup and why it
works, put them to the group as my experience with shunt fed towers is
almost nil!

I have a 48' Delhi Self supporting tower, TH6DXX @ the tower top and 6m beam
on top of the 16' mast that extends past the trust bearing. See yesterdays
posts for FULL description and link to URL with a .jpg photo
Electrically this is all maybe 80'-90' tall (?)
I attached a piece of 3/4" PVC at about the 34'-35' level.
I attached a #14 AWG insulated stranded wire to the tower at this level and
fed it throught the PVC and brought
it down vertically to ground level at aprox 2'-2.25' out from the side of
the tower.
I brought my coax from the shack and inserted a 800pF air variable in the
center line between the coax and the gamma wire.
I attached the braid of the coax to about about 27,   127' radials that are
laid upon the ground.  (65' radials would likely work just as well, but
these were already there, for my 160m antenna)
I was "reminded" (blush) to ALSO attach the braid of the coax to the bottom
of the tower, which I did.
The cap is barely meshed (lowest capacitance) for resonance @ 3.525MHz. SWR
is below 3.1:1 @ 3800MHz
Moving the cap 1/2" (roughly) moved resonance from 3.450 to 3.525 (quite
touchy)

Not dark yet so hard to tell if it works, but the USB Coast Guard signal on
3.485 is now louder on my tower than on my
160m antenna (a good thing!)

More later after I've had time to play with it.

Again thanks to everyone who sent 100% helpful suggestions.

MIKE VE9Antenna Antenna.
> >
> > In all my rush, I had forgotten that the braid of the coax actually
connects
> > to the base of the tower as well as the radials.
> > (I just had it connected to my radials only-ooooops!)
> > I appreciate several SHARP hams pointing that out so eloquently to me.
DOH !
> > I feel so stupid. (and no one made fun of me)
> > At least I got a good workout up and down the tower.
> >
> > Attached the braid to bottom of tower;, went in the shack, SWR FLAT at
> > 3.450MHz.
> > Barely touched cap with minimum engagements of plates and it's FLAT at
3.525
> > and rises to just over 2.5:1 at 3.800MHz
> > (which I rarely wander up to anyway)
> >
> > Thanks for everyones advice.
> >
> > Think I'll try it out tonight.
> >
> > Can hardly wait for it to get dark now.
> >
> > Mike Ve9AA.......
> >
> > Michael, Coreen &amp; Corey Smith
> > 271 Smith Rd.
> > Waterville, NB
> > Canada E2V 3V6
> >
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> Kelly Johnson
> N6KJ
>