[TowerTalk] Rohn AS25G inside a 25G tower

Sun May 10 07:24:33 EDT 2015

Thanks ROger,

Again this is an 8 foo tlong mast going inside a 9 foot top section, so therefore the rotor plate 
must go somewhere in th emiddle in the section of 25G and this is not obviously possible to 
do...

Several folks e-mailed me off the list. They too apparently have never run across this 
problem...

Here is another reminder of the issue from Bruce Ferratt, facing a similar situation to mine 
with an AS25G (although I am not needing a thrust bearing) from this group a few years ago:

>>Hello.
If one wants to use a thrust bearing on a Rohn 25G and have a rotor plate 
too, the accessory shelf will only fit at the very top of the 'top 
section',... this is where there is no zig-zag/crossbar in the Rohn 
tower,... or down at the very next section (9-10ft down)  One needs to use 
two (2) shelves for this configuration.  The only way an AS25G plate will 
fit about 4-5ft down in the top section is if you: 1) cut a crossbar 
out,...OUCH! and there goes the integrity of the top section ( I guess you 
could re-weld this back) or, 2) cut the plate down and notch it for the 
rotor install.

I think that using a mast that goes down further inside (10ft to the next 
section) is overkill for my application.  I am mounting a Tribander with a 
stacked vertical for 2m/440. Thanks for your recommendations!
73
Bruce
K4BOF

On 10 May 2015 at 6:55, Roger (K8RI) on TT wrote:

> 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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