Hi Roger,
Oh I know where you are coming from. I agree. Someone mentioned (at
a recent club meeting) that he once saw someone selling a kit for that
purpose. I'm just more interested in the concept and such and if anyone
had seen anything like that. Maybe the fact that none of us has seen or
heard of such a thing in the last few years is a clue about whether it
works or not. :-)
I regret getting rid of my old EZWAY 55 foot crank up tilt over tower
years ago. Anyway, after that club meeting a bunch of us were
discussing this odd-ball tower and much of what you alluded to came up.
Currently I have a home made tilt over Rohn 25. It's 30 feet tall and
has about 18 feet of mast coming out of the tower's top thrust bearing.
I made a tilt over fixture similar to that of the commercial crank up
and tilt over systems. It works fine. And I raise and lower the whole
tower with a 1/2 inch cordless drill. So there is no electric motors
etc. When I want to lower it I use a 5/8" socket instead of the winch
handle and that provides the power to drive a worm gear winch.
At this time, I only have the 6-meter beam up. The 2m and 70cm Yagis
are in the garage being worked on.
Still the thought of a couple of Rohn 45s with a hinged base and a
couple of Rohn 25s telescoping into them with a 5 foot overlap, would
give me the same height I currently have. I would be able to nest it and
lower and raise it easily.
The existing tower is bracketed to house at the 13 foot level.
73, Rich WA1TRY
On 7/15/2011 1:02 AM, K8RI on TT wrote:
> 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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