Topband: Tower Shunt Feed

[Guy Olinger K2AV]

Haven't said a blessed thing about your radials, which will make or
break it.  Someone talked about a problem with using a SteppIR on top
of a loaded tower.  Been a while and don't recall the particulars,
probably should search the archives.

73, Guy.

On Sun, Apr 3, 2011 at 12:29 PM, Jerry Keller (K3BZ) <k3bz at verizon.net> wrote:
> I want to try a shunt feed on my 60' aluminum freestanding tower topped with
> a 4 element SteppIR. The tower is a Heights and it tilts over on a 4' high
> top-hinged base. I've come up with the following specs I dug out of K1ZM's
> book "DXing on the Edge":
>
> (1) Three #14 stranded insulated wires spaced 15" from tower leg and shorted
> top and bottom as an 8"-on-a-side triangular cage, running from top of tower
> down to where the tower joins the hinged base (4' above earth level because
> of the hinge). That would make the shunt 56' high.
>
> (2) I'd like to use an omega feed with air variable caps I liberated from an
> old tuner.  I notice that most often vacuum variables are used for this
> rather than air variables. The plates in the air variables I have are spaced
> about 3/16".... will they handle a KW without arcing?
>
> (3) I want to put the feed caps in a plastic box at the 4' level so the
> shunt won't interfere with tilting the tower over.  The tower grounds and
> the radial system would connect at ground level to a flexible copper line
> running from ground level up to the feed box.  Would that work OK at 160M?
> If it's important, I could run the shunt the full 60' down to ground level,
> but it's mechanically more difficult.
>
> (4) With this arrangement, how important is the SteppIR? Would I need it for
> top-loading?  The SteppIRs elements "float" above the grounded boom...
> should I plan to ground them to the boom?
>
> Advice, alternatives, comments?  Any input appreciated.
>
> 73,  Jerry K3BZ
>
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