[TowerTalk] Rohn AS25G inside a 25G tower

Sun May 10 14:44:23 EDT 2015

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 at teleport.com
>>>
>>>
>>>
>>> ------- End of forwarded message -------
>>>
>>> _______________________________________________
>>>
>>>
>>>
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>>
>> -- 
>>
>> 73
>>
>> Roger (K8RI)
>>
>>
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73

Roger (K8RI)

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