|[AMRadio] do not ground tower|
bcarling at cfl.rr.com
Wed Jun 14 12:49:54 EDT 2006
For my 160m shunt fed tower I had a Rohn 25 - a 60 footer
with a few feet buried in concrete...
So I dug out some old articles on how to do it.
Now, I DID have a good capacity hat in the form of
a 4 element Swan TB4HA beam at the top.
AND an 11 element Cushcraft bean on 2m FM above that.
I had deliberately installed insulators on the guy wires,
so that was not a problem.
Ran a piece of #12 gauge solid copper wire up the side
about 12" off the tower to a copper pipe standing off
at about the 40 or 50 foot level and attached firmly to
the tower with two U bolts. This is all from memory.
There was a sreries variable capacitor at the bottom of
the shunt line, and it worked really well. Flat SWR
anywhere I wanted on Top Band!
73 de AF4K, Bry
Don K4KYV writes:
> I prefer the base insulator and series feed myself. Shunt feed or unipole
> feed works great if the tower is close to a resonant length. It becomes
> more difficult if the tower is much shorter than natural resonance.
> Sometimes top loading will make shunt feeding easier, since it raises the
> resonant frequency of a short tower. Series feed, if you can find an
> insulator, gives you a lot more options in tuning up the tower.
> Of course, if you are stuck with a typical ham radio style jury rig where
> the bottom section was embedded several feet into the concrete base, you
> have no choice. Unless the tower is short enough to stand without guys,
> that is about the worst possible way to erect a tower. A tall guyed tower
> is subject to much additional stress when the base is rigidly set in
> concrete; it cannot sway or rotate in heavy winds, and that can cause
> failure of the tower structure. If it is mounted with a base plate and pier
> pin, or a ball-and-socket insulator as AM broadcast towers are constructed,
> the base of the tower can follow the movements of the tower instead of
> having the entire tower bend and twist under high winds.
> Don k4kyv
> This message was typed using the DVORAK keyboard layout. Try it - you'll
> like it.
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