Hi Rick,
Your observation about Rohn 45G handling less than 25G as read in you Rohn
book is not a misprint. If you look close, you will see a couple of other
things. One is that 45G includes some more hardware (sidearms) and
feedlines in their ratings than 25G does. If you don't use that many
feedlines or that much hardware, you can use more square feet of antennas.
Another thing to look at is that the 45G has only two sets of guys and the
25G has three sets. Also, notice where the top set attaches. On the 45G,
it is down 15 feet at the 85 foot level while on the 25G it is down only 5
feet at the 95 foot level.
Also, and very important, the diagrams given the the Rohn book are but a few
of the thousands of possible ways to put up Rohn towers. For example, you
could guy right at the top of the tower and use more sets of guys below the
top set than Rohn specifies in their examples. This will strengthen the
tower A LOT. Determining exactly how much is an exercise for a professional
engineer. Rohn can tell you but it will cost you more than you want to
spend to find out from them.
One of my Rohn 25 tower is 102 feet out of the ground I have four sets of
guys on it. Very strong. Five Yagis for 10 and 15 meters on it plus a few
VHF/UHF verticals and a couple of wires. It has been up in lots of wind
since 1973.
Stan w7ni@teleport.com
Rick Bullon wrote:
> First I would like to again thank all who helped me on my trig
> question post. After I took the info and plotted out my proposed 70ft
> Rohn 25 tower, it took up less area than I thought so now I'm going to
> change plans and go up to 100ft!!
> I tried to use the formula I received from the list but I guess I am
> stupid when it comes to trig. I couldn't get the new dimensions right so
> I figured if the old guy points of 56ft ( rohn 25 at 70ft 70 mph) and
> the new guy points are 80 ft ( Rohn 25 100ft 70mph) the difference is 24
> ft, so if I add 24 ft to the distance from the property line ( which the
> old figure was 28ft)this would move the tower to 52ft Right? or am I
> totally wrong again?
> Next question, from my last post I see that "I" beams are the way to go
> for elevated guy points. I forgot to ask what size "I" beams to use.
> If I use Phillystran for the top guys then I can use the 3/16" EHS for
> the other guys right? and I think I read on here somewhere than the cost
> is about of using Phillystran is about the same as using the EHS &
> insulators to brake up the guys Right?
> I noticed something strange while studying the Rohn book the other
> night. I was looking at the difference between Rohn 25 @ 70ft and 100
> ft, I mistakenly open to the Rohn 45 section instead of the Rohn 25
> section I noted the the allowable area for round and flat member is
> higher for Rohn 25 than for Rohn 45 at the same height is this a
> misprint? My book is dated Dec 1997
> Another thing with the current thread on rebar cages I noticed that the
> Rohn book doesn't call for one. I can only assume that the rebar cages
> are for crankups or another brand of tower or is this another issue I
> have to consider? I wasn't planning to use one in my plans.
> Well again this post is longer than I had planned I will probably have
> more questions later HI HI
> I know it has been stated before but this is the BEST place for info on
> towers and antennas anywhere Thanks again guys!!!
> 73
> Rick
> KC5AJX
>
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