[TowerTalk] Rohn AS25G inside a 25G tower

Sun May 10 06:55:54 EDT 2015

It's been awhile, but IIRC I had no problems installing the shelf made 
for the 25G in the 25G.  I had to shim the 45G shelf in the 45G with 
1/8th in X 1" shims, but nothing on the 25G.  It was a snug fit and took 
a little moving the shelf around to get it in place.  I did install the 
shelf some 5' below the top .  I used the flat plate top on a regular 
tower section as I do in the 45G.

I'd like to find a fold over, crank up to replace the 100' 45G.

73

Roger (K8RI)

On 5/9/2015 9:21 PM, Bry Carling AF4K wrote:
> Greetings - This is not a new topic by any means, but here is my dilemma:
>
> I have a Rohn 25AG2 top section (I believe) and also a 25ASG rotator shelf both courtesy of
> Bill K4XS.  I would like to install the shelf plate inside a 25AG2 (I think it is) top section that is
> 9 feet long, to support my HAM-M rotator. I also have a nice alloy mast from Bill that is 8 feet
> long and 1.5" diameter. I would like to have the mast stick out a few feet above the top of the
> tower. This seems to not be easy to accomplish. The rotator shelf will not go into the tower
> section. There seem to b esome hack solutions that might work, but...
>
> I have read a few horror stories from fellows trying to install the HAM-M and rotator plate
> inside a 25G mast.  What is the best approach to this, given that the plate will not go inside
> the tower section?
>
> ANY insights would be deeply appreciated... Here is the history I found from this list. There
> was discussion about cutting away part of the 25G's horizontal or diagonal braces in order to
> install these items. That sounds like a bad idea.  What is the best solution please? Perhaps I
> am missing something here...
>
> Brian Carling, AF4K
>
>> I am getting ready to install a Ham-4 rotator in a Rohn 25AG3 top section.
>> The 25AG3 doesn't have enough room in the "open" area at the top of the
>> section to accomodate the height of the rotator.  The rotator is too big to
>> push down further into the tower and will not rotate inside the tower except
>> where the tower sections join together.
> >From reading later messages on this subject, it appears that your top is not
> really a 25AG3.  Later, you said you thought it was a 25AG.  In fact, I am
> reading lots of confusing data on this relector about Rohn tops that does
> not agree with my Rohn book.  For example, K7LXC says there are 5 Rohn tops
> and I think there are 6, not counting the short tops.  My book says there is
> a 25AG, 25AG1, 25AG2, 25AG3, 25AG4, and 25AG5.  All of them are "pipe tops"
> of one sort or another except the 25AG4 which is a "flat top".
>
> On two of them, the pipe extends down into the top section far enough to
> probably interfere with installing a rotator.  These two are the 25AG1 and
> the 25AG2.  The 25AG1 has a piece of standard 1 1/4" pipe installed in it
> and it is too small to accept a 2 inch OD mast.  The 25AG2 has a 2.25" OD 14
> guage pipe and it WILL accept a 2 inch OD mast, so I conclude that you must
> have a 25AG1.  But you also said you were using 1 1/2 inch pipe for a mast
> and have to shim it.  This is confusing since 1 1/2 pipe will obviously not
> fit inside of a 1 1/4 inch pipe which is what the 25AG1 has.  I believe you
> also mentioned you got a second top used real cheap and it had a large hole
> in it.  So do you have one top or two and which one is it?
>
> Another thing you said was that you were using 1 1/2 inch pipe for a mast.
> DON'T.  I believe that would be water pipe and there has been TONS of
> information about problems with using water pipe for masts, not to mention
> they don't fit without shims into a standard 2 inch thrust bearing, 2 inch
> ID pipe top, or any Ham-M, II, III, IV, or Tailtwister.  Rohn makes a 10
> foot mast (M200H) that will work for most modest installations.  If you need
> something stronger or longer than that, talk to K5RC at Productivity Resources.
>
>> It looks like the best place for it is at the top of the "next to top"
>> section. The rotator should rotate freely there, but how do I get it in or
>> out without lifting the top section and the antenna?
> I have two Rohn 25 towers with rotators installed at the top of the section
> just below the top section.  One of them has a Tailtwister in it and the
> other has a Ham IV.  They both work just fine and have for 23 years.  To get
> the rotators in the tower, I cut one of the horizontal braces out of the
> bottom of the top section (and yes, Steve, you DO have to cut a horizontal
> brace out to get the rotator mounted in this location.)  I did not bother to
> reinstall the cut brace and it has not caused me any problems so far.
>
> Other items worth commenting on are these:
>
> I agree with Steve, K7LXC, that a Ham M, II, III, or IV can be squeezed into
> a Rohn 25 just about anywhere without cutting any braces.  I have done it.
> The only place it won't fit is through the "square" formed by the horizontal
> braces at the top of one section, the horizontal braces at the bottom of the
> next section above it and the tower legs.  I never thought I could get the
> rotator inside the tower through one of those "triangles" either, but it
> will go if you do it right.
>
> Another comment I have seen is that once a Ham IV is inside of Rohn 25, it
> will "free fall" down the inside of it.  Not true.  The "ears" on the Ham IV
> casting are too large to go past the horizontal braces.  This is why you
> have to cut one horizontal brace out of the top section to put a Ham IV at
> the top of the second section from the top.  You can get the Ham IV inside
> the tower OK, but you can't slide it down past the set of horizontal braces
> at the bottom of the top section.
>
> Yet another comment from Steve is that the AS25G accessory shelf will mount
> just about anywhere inside a 25G section.  I don't agree with this statement
> since the AS25G interferes with the diagonal braces which are almost
> everywhere in a 25G section or top.  Of course, you could modify the AS25G
> by cutting away some metal to clear the diagonal braces, or you could cut
> out another set of diagonal braces so a standard AS25G will fit, but I would
> not recommend this since it would weaken the tower considerably.
>
> I have designed a prototype of a new Rohn 25 rotator shelf which clears the
> diagonal braces in 25G and would truly allow installation of a Ham IV just
> about anywhere in a 25G section or top without cutting out any braces at
> all.  Maybe I should consider making a production run of these shelves since
> it seems to solve a common problem for which there is currently no easy
> solution.
>
> Is there a demand for such a self priced at about $40?
>
> Stan  w7ni at teleport.com
>
>
>
> ------- End of forwarded message -------
>
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73

Roger (K8RI)

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