[SEDXC] Tower Question

[Bill Coleman]

On Jun 25, 2007, at 5:14 PM, Jeff Carter wrote:

> One of the recurring themes of ARS lore is that it's incredibly  
> important to
> spend your effort/time/money in your antenna system rather than  
> anywhere
> else.  If you're interested in DX, the antenna system is the way to  
> go,
> according to the literature.

Hmm. You can work a lot of DX with crummy antennas if you spend a lot  
of time and are very, very patient. Good antennas help to speed up  
the process and present you with more opportunities. Having the best  
possible antennas is likely more critical for contesting than DXing,  
but a decent antenna system offers the best increase in effectiveness  
per dollar spent.

> What I have so far:
>
> A Tri-Ex 71' Crank Up Tower

Crank-ups are an interesting trade-off. They are complex, heavy and  
allow limited antenna loads at higher wind speeds. Big antenna  
systems dictate either massive self-supporting towers or guyed  
towers. For modest installations, you might consider a bracketed  
tower system.
> A Cushcraft A4S
>
> (no pix, but I've ordered the rebuild kit from Cushcraft)

The A4S is likely the best of the medium-sized tribanders from the  
cut-and-try era of antenna design (ie before computer antenna  
modelling became practical). It is lightweight, reasonably effective  
and relatively strong for its size.

> No rotor/thrust bearing/whatever yet

Any of the standard rotators should be able to turn an A4S without  
problem. Don't use a TV-type rotator, but likely something with a  
brake or worm gear. Any of the HAM series would work (HAM-M, II, III,  
IV, Tailtwister), HD73, or just about any of the Yaesu rotators.

> There are a dozen sites that lovingly detail the installation of a  
> tower, but
> while they are all similar they are all different, too.  My tower,  
> as you can
> see from the pictures, is older and is thus no longer supported by
> engineering drawings.  The closest thing seems to be the LM-470,  
> but the
> detail in the engineering drawings for the base isn't really clear  
> to me.

One thing you can do is run over to http://www.contesting.com and  
look up the archives for the TowerTalk reflector. TowerTalk has been  
an active mailing list for over 11 years and just about any tower  
topic has been discussed at length there.

The K7LXC prime directive on tower construction is "Do what the  
manufacturer says." So, your best course of action is to determine  
exactly what the manufacturer required for your tower system.

> Is there a site I've missed that has good newbie tower base  
> information?  The
> only time I ever did concrete was putting up 12' satellite  
> dishes...this is a
> quantum leap, and I'm very aware that once I've poured 4 yds of  
> concrete,
> it's forever.

You might want to consider contracting some of this out. You  
certainly don't want to mix yards of concrete by hand. For a self- 
supporting tower of this size, you'll need a large rebar cage --  
there are companies that can make these for you.

You do need to find the exact base specifications from the  
manufacturer. Your tower derives all of its support strength from the  
base, so you have to get that part right.

> I'd be particularly interested in the experiences of anyone who has  
> put up a
> similar tower.

I decided against a self-supporting tower in part because I didn't  
want to create a huge concrete monument in my yard. I have a 15m high  
tower bracketed to my house with an A3S. For the next QTH, I'd like  
to put up a guyed tower (or two).

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901