Try one of the NA4RR Hexbeams http://www.k4hex.com/home.asp. The Hexbeam
doesn't want to be much above 30-35 feet for optimal performance and is very
light weight. At our Field Day we had one at 20 feet that clearly out
performed a tribander at 36 feet. We found the Hexbeam to be very
directional. Could hear off of the sides and back, but it really wants to
talk off the front. Found Guam with a good pileup going and got him twice
on 20 meters (GOTA and regular) each on the first call. Same for the 4
Hawaii stations we found. My bet is there is some parasitic influence from
all of the extra reflectors and the extra driven elements acting as
directors (the Hexbeam had wires for 6/10/12/15/17/20 on it)
Gary J
N5BAA
-----Original Message-----
From: Alex Malyava
Sent: Wednesday, August 26, 2015 10:50 AM
To: TexasRF@aol.com
Cc: Douglas M. Ruz Sobrado ; towertalk
Subject: Re: [TowerTalk] How many tower sections i can install??
since we are talking about 30' short "tower" on the building roof, why not
to use some sort of pipe instead of pretty heavy Rohn sections?
I don't think it is a big deal to find or weld 9-10-12m long tubular mast
that will be able to support a spiderbeam or some other lightweight
tribander.
On Wed, Aug 26, 2015 at 11:22 AM, TexasRF--- via TowerTalk <
towertalk@contesting.com> wrote:
Hi Douglas, you can achieve a a greater guy point distance by using four
guys instead of three. You would not want the guy to guy angle to exceed
120
degrees in any case.
Your roof dimensions would allow guy to guy angles of 120, 60, 120 and 60
degrees. With the tower mounted in the center of the roof and assuming the
anchors are at the edge of the roof, a guy to guy angle of 120 degrees,
the
distance would be 20.0 ft to the anchor. The distance between anchors
would be 34.6 ft, 20 ft, 34.6 ft and 20 ft.
So, in this case, you could guy the tower a couple of ft below the top and
three 10ft sections would have a anchor/height ratio of 66.66%.
We typically use an 80% ratio mainly because that is the number Rohn
specifies for all of their tower models. It is a good compromise between
load
capacity and space required.
Considering that these towers are used up to 180ft in height or more, it
is
reasonable to move anchor points inward for reduced heights. The issue in
doing this is that Rohn has no published data for doing this. The wind
load
rating has to be reduced and it takes engineering skills to properly do
the calculations. It is not rocket science however.
I would be concerned about possible roof damage as much as the tower
surviv
al. It is conceivable that using the roof edge as a turning point for the
guy and then a ground anchor would be stronger. Something else that would
benefit from an engineers blessing.
73,
Gerald K5GW
In a message dated 8/25/2015 9:14:22 P.M. Central Daylight Time,
co8dm@frcuba.co.cu writes:
Hi,
I would like read your ideas.
I have few 10 ft section of a tower (it is like a Rohn 25G).
I would like install few section over some part of my roof...The roof is
concrete...as you know many house in the Caribbean has concrete roof
...it
is 24ft by 40ft...so, i have calculating and the distance from the base
to
the guy anchors is 14 ft !!!
I know the distance from the base to anchor points is 70 % of the tower
height...so, 70% of 20 ft is 14ft, that´s mean 2 tower sections...right
??...Is it possible install 3 sections adding more guy´s set ???
Thanks,
73....Douglas, CO8DM
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2015.0.6086 / Virus Database: 4409/10515 - Release Date: 08/26/15
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|