I remember inserting the shelf between braces. and having to move it up
or down about a foot, or mount it just above the joining of the two
sections which would put the mast up about a foot which would be a bit
short. Depending on your mechanical aptitude, (not every one is great
with tools) cutting metal away is no big deal. I'd just use a high
speed grinder, Dremel tool, or Rat Tail file, to cut away the small
area to clear the brace (leave about 1/8th in clearance) which is a
simple job. It "may" make the orientation of the shelf side dependent.
IOW, it will only fit one way instead of three. IIRC you could even cut
an 1/8th or even a 1/4" off the edges of the shelf. It's not necessary,
but looks neater. As I now have a Milling machine, I'd probably go that
route. If relegated to files, I'd use the Rat Tail and only remove the
necessary metal. Spray the exposed steel with "cold galvanizing to
protect it. Even use self etching primer if you have some. It's not as
pretty, but if you have it, use it and then paint over it.
One other option and the logical approach is to simply use a longer mast
unless for some reason you are obligated to use the 8 footer. I know
it's done and large antennas are mounted on 25G, but 25G is listed as a
light duty tower by ROHN, so an extra strong mast should not be needed.
Cutting a brace is not an option to me. Why cut a brace which is
structural? You are trying to fit a shelf or metal plate, which is not
structural, into a tower section. It makes sense to cut the non
structural insert/shelf/plate. I do remember that I could not insert
the rotator (Ham IV) between braces and had to lower it down through the
section while others could (It's in the archives), so there must be some
variability in the brace spacing, or 25G look alike towers. In your
case if the rotator would not fit between the braces, you would need to
insert the rotator first (from the bottom of the section and move up the
section, then insert the shelf where it would fit modified if necessary
as I don't think lowering from the top is not an option.
I just think of working with steel as if I'm working with hard wood.
Really hard wood! <:-))
73
Roger (K8RI)
On 5/10/2015 7:24 AM, Bry Carling AF4K wrote:
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@teleport.com
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Roger (K8RI)
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