[TowerTalk] question of the day

[jimlux]

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