Roger (K8RI) wrote:
>>
>> W3GM had six 100' Rohn 25g towers, all of which used a ground mounted
>> rotor.
>> Ham 4 and Tailtwister, as well. They were turning things like a 3
>> element full sized
>> 40m yagi. The "mast" was 2" irrigation pipe. Wasn't particularly
>> heavy, nor thick
>>
> I hope he had the rotators mounted independently of the 25G. IOW, the
> rotator mount affixed to the concrete and not the tower (It did say,
> ground mounted). A full size 3L 40 could likely over stress the 25G in
> shear with a base mounted rotator attached to the tower. In addition
> the 25G is a pretty light tower for that much wind load
>
> I'd not put a 3L 40 on anything smaller than a 45G
>
> 73
>
> Roger (K8RI)
>
Having six 100' towers implies a fair amount of open space, where a
failed tower might not do much damage other than to the tower. He could
just gamble that a big wind won't come up, and if it does, and a tower
gets tweaked or falls down, you can just replace it.
Just looking at rough ballpark numbers.. 10 feet of 25G costs about
$125, 10 feet of 45G costs about $250, so, for a 100 foot tower, the
cost difference is around $1250. If labor is free(!), and you get a big
wind every 10 years, then the annualized cost of cheaping out on the
tower is zero. (aside from the cost of breaking the antenna)
Not everyone needs a tower that is suitable for commercial installation
next to a preschool.
Jim, w6rmk
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