In a message dated 5/30/01 5:20:42 PM Pacific Daylight Time, w5kp@swbell.net
writes:
> The question is: Structurally, is it a bad
> thing to put the guys for the 74 footer at the right distance from the
tower
> for a 100 footer now? If I did, that would put the guy anchors at 80'
> instead of the 56' specified, which is a pretty hefty distance change.
It's all relative. The Rohn specs for guy anchor placement at 80% of
tower height is just ONE scenario. You could have guy anchors anywhere from
25% or so to 200% or so of tower height and properly engineered, any of them
would be fine.
> Common sense tells me the stress on the tower
> goes down as you move the guys further out,
That's mostly right. I think there's less stress on the guys too.
If you're going to have a populated tower with other yagis down the
tower, then having shallower guy angles is very helpful to provide more room
under them for turning side-mounted antennas.
> but I suppose there's a
> practical limit due to sag and who knows what else.
That's mostly right but being a non-engineer I'll let someone else answer
that.
As was already pointed out, put the guys as high up the tower as you can
- preferably at the top. The Rohn scenario is for commercial installations
and not necesarily ham ones. Also check the general notes and you'll see that
Rohn has deducted 8.0 sq.ft. for a symmetrical mount already so you can add
the 8.0 sq.ft. back into the figure for tower capacity; i.e., if it says the
tower will take 12 sq.ft. in the little height/loading drawing, then add the
8 sq.ft. so you really have a capacity of 20 sq.ft. for ham purposes.
Cheers & GL, Steve K7LXC
Tower Tech
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