On 7/15/2011 12:07 AM, Richard H. Aubin wrote:
> Has anyone ever heard of a non-Rohn 3rd party "kit" that would allow you
> to telescope a Rohn 25 into a Rohn 45 ? A couple of us were discussing
> this at a club meeting and one of the guys in our club said he had seen
> a guy selling these kits at a hamfest once. This was several years ago.
Unless I'm missing something: The question this raises is what would be
gained by telescoping a smaller guyed tower into a larger guyed tower?
No matter how I look at it the answer comes out: Zip, nada, nothing!
Neither tower is rated as non guyed any more, but going back to the old
figures IIRC the 45G was rated at some what less than 40 feet unguyed,
but the antenna wind load was only a couple square feet. Adding one
section of 25 G would put you beyond that so you are still limited by
the loading of the larger tower which is already at it's maximum.
From extending a guyed tower you then limit yourself by the 25G so why
bother with the 45G, or if you need the strength of the 45G why bother
with the 25G. Plus cranking up the smaller tower out of the larger would
require some sort of locking mechanism, not just a pull up cable and
that cable would take the entire vertical component of the guying force
on any guys attached to the 25G. Neither tower is engineered for that
kind of application.
The 45G could be used as a hinge over base for a 25G, but again, the 25G
is capable of serving as a hinge over base for a 25G fold over.
Even with a well engineered adapter to fit the 25G inside the 45G it's
not a self supporting tower.
Compare the structure of the 45G with a 50 foot crank up rated for 25 or
30 sq ft of antennas. They may be smaller at the top, but they are
built like a tank and seem to weigh darn near as much. They also set in
or are bolted to a far larger chunk of concrete, usually with long
"J-bolts" embedded in the concrete.
IIRC the taper is such that when a section is at maximum extension it
fits tight into the outer section. Many require "pull down" cables as
gravity is not reliable for pulling such a tight fitting structure down.
I stated earlier that I'd not hesitate to build an climb a tower, Even a
large crank up, but I'd not climb a 25G/45G even to the junction.
From my view: As well as looking impractical from a strength approach,
mating a 25G to a 45G sounds like an accident just waiting to happen.
73
Roger (K8RI)
>
> It's an interesting concept. I would think something like that would be
> a legal nightmare. (Liabilities etc.) However I'm thinking one could
> home-brew something.
>
> - Rich WA1TRY
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