Steve -
Check the Rohn drawings, but I think you'll get a couple of extra feet with
the new 25G straight section and small flat top plate (About 10' vs 8') vs
the 25AG-4. Also, if you ever want to grow the tower, all you have to do is
move the small flat plate, rather than removing the whole top section and
reinstalling it later.
On the other hand, the 25AG-4 may provide some better access to rotator,
etc., since the top two Z brace sections are not Z-braced but open. This
also allows you to more easily install two rotator plates with a thrust
bearing on the top plate and rotator on the bottom plate. With a second
thrust bearing the top flat plate of the tower section, the mast and
antennas are now completely supported without any rotator. Removing the
rotator for maintenance is now no problem (of course find a way to keep the
mast from turning while you do this!). I use this arrangement on my towers
and it works great.
The TB-3 is a good thrust bearing. Have used them for years with no
problems.
73, Bob - W3YY
.
----- Original Message -----
From: "steve sala" <stetrekve@yahoo.com>
To: <towertalk@contesting.com>
Sent: Sunday, June 01, 2003 21:25
Subject: [TowerTalk] rohn flat top sections
> I am going to exchange my pointed 25AG3 top section
> for a flat section so I can use a thrust bearing. I
> have two choices: 1)Replace my 25AG3 top section with
> another regular 25G section and use the small flat top
> BPL25G bearing plate with it or 2)Just use the 25AG4
> flat top section. Does anybody have an opinion on the
> pros and cons? I have the extra regular 25G section
> here so I would only have to pay freight for the small
> bearing plate to get it here while if I used the
> regular 25AG4 flat top section, I would have to pay
> the freight for that heavy section. Would both be
> comparable for holding the same antennas? I have the
> 85 foot tower guyed per the Rohn book at 30', 60', and
> 80' (the book published when I put up the tower 25
> years ago). Since I will be using a Force 12 5BA 5
> band Yagi just above the top of the tower with a
> lightweight M2 7 element 6 meter 6M7JHV Yagi antenna
> above that and a M2 9 element 2 meter 2M9SSB Yagi
> above that, again, would it make any difference how I
> achieve the flat at the top? Either way I would use a
> TB3 thrust bearing for the 2" OD steel mast.
> 73 Steve K7AWB Spokane Valley,WA
>
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