Hi, Pete.
I'm kind of sorry I even wrote my post now for the confusion it has
apparently created, but just to clarify ... I was putting up a 70 foot
AN Wireless self-supporting tower (model HD-70). It's basically a
heavier version of the popular Trylon towers, and both have the same
issue. You encase the base in concrete before you ever add the rest of
the tower, and the eventual "plumbness" of the finished tower is a
function almost solely of how accurately you plumb the relatively short
base (five feet in my case) before the concrete is poured. My tower
tapers from 48 inches on a face at the base to about 22 inches at the
top, which calculates out to a leg angle right at 89.0 degrees. Every
0.1 degree of error therefore gives about two inches of offset at the
top, and obviously anything beyond a full degree of error (pretty easy
to get with many alternate methods) would put, in my case, a 2,000 pound
tower partially leaning out over one of the legs ... with no guy wires
to help support it.
The $40 digital angle gauge I used worked very well for the task and I
just thought I'd pass it on in case anyone else was ever going to put up
a similar tower.
73,
Dave AB7E
Pete Smith wrote:
> When I put up my 97-foot Rohn 25 tower on a pier pin base (my first and
> only experience of this kind), the experienced tower builders who were
> helping me said absolutely nothing about plumbing the tower with any kind
> of instrument. When it was up and all three guy sets were installed, one
> guy stood at the base looking up the tower while 3 others adjusted the
> turnbuckles at the guy anchors to get it approximately straight and
> vertical. Once it looked OK, each one tightened his turnbuckle by the same
> number of turns until the guy tension (measured with a Loos Gauge) was
> correct.
>
> I am wondering how important all this emphasis on precision really is?
>
> 73, Pete N4ZR
>
> PS that was in 1995. The tower carries a short 40M 2-element yagi and two
> short boom tribanders, one on a swinging gate side-mount. Max wind gusts
> encountered since have been on the order of 75 MPH.
>
> At 10:59 PM 1/21/2008, Its from Onion wrote:
>
>> When I need to 'plumb' a tower, I use my transit. Set it up about 150
>> feet from base
>> and shoot any point of the tower.
>> They can be rented rather cheaply if you cant borrow one.
>>
>> Just my 2 cents.
>>
>> Lee
>> KE4VYN
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