In a message dated 97-08-06 18:57:53 EDT, you write:
> I'm planning a second tower which would consist of 100' of Rohn 45G. On
top
> I would put a 40-2CD (at 110' on a mast) and at the bottom of the mast at
100'
> a 4 or 5 element 20 meter beam like a 204BA/205BA.
> Looking at Rohn's drawings for a 100' tower with 90 MPH wind speed,
> they show the tower guyed at 31', 61', and 91'. They indicate that the
tower
> will support 13.5 square feet of round member antenna. Is this 13.5 square
> ft at the 100' level? In my case the distance between the top guy point
and
> 40-2CD would be 19'.
> The question I'm leading to is, would it be wise to move the guys up
> the tower a bit to accommodate my proposed antenna configuration? For
> instance, guys at 37', 67', and 97'? It seems like there is a lot of
antenna
> above that top guy.
Hi, Ken --
I'm posting your quiery to TowerTalk as you are asking some questions
with not so obvious answers.
First of all, the drawings in the Rohn catalog for 45G and 55G are
configured for commercial applications. There are two significant
implications of this.
Number one is that the tower capacity in square feet has already had 8.0
square feet deducted for a commercial sidearm antenna mount. In other words,
you can ADD the 8.0 square feet back into the tower rating since you're not
going to be installing that type of hardware. So if the figure on the drawing
says 12.0 sq.ft., adding the 8.0 sq.ft. back gives you 20.0 sq.ft. of total
tower capacity. This applies to 45G and 55G only; not 25G. Check the notes
under the drawing for more information.
The other implication is that the reason that there is 5 feet or so of
naked tower above the top set of guys is for the same reason. That
configuration allows the aforementioned commercial sidearms and antennas to
be installed so that they are clear of the guywires. For ham purposes, my
recommendation is to go to the top of the tower with the top set of guys.
Yes, you can adjust the placement of the lower guys to equalize them without
upsetting any engineering.
My understanding is that the tower capacity is for the whole tower.
> One final thing if you have it handy, my Aug 95 Rohn catalog does not
> have the wind map for the US. Any idea what Stafford county Virginia is
> rated at? The 70 MPH package shows only two sets of guys. I think I'd
feel
> safer with the third set. Might also add a second 20 meter antenna (stack)
> at a later date.
>
Stafford County is only a 70 MPH wind speed zone but it's within 100
miles of hurricane oceanline. I'd probably build to a higher wind speed just
to be on the safe side.
73 and GL, Steve K7LXC
TOWER TECH -- professional tower supplies for amateurs
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search
|