[AMRadio] do not ground tower


Brian Carling 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
> 
> 
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