[TowerTalk] Rohn AS25G inside a 25G tower
Joe Subich, W4TV
lists at subich.com
Sun May 10 09:42:52 EDT 2015
The Rohn 25AG2 section has a 2' 9" length of 2.25" OD x 2.06" ID tubing
for a "nose". The only place the AS25AG accessory shelf will fit is in
the 1' 3 3/4" open space right below the top tube with the "ears up" -
unless you decide to cut the diagonals out of one bay down the section
or notch the side of the AS25AG to fit around the diagonal bracing at
the specific install point.
In practice, it's necessary to remove one set of diagonal bracing on
the 25G sections to install/replace a rotator at any place other than
the very top in any case because most rotators are too large to fit
through the bracing or rotate once in place.
73,
... Joe, W4TV
On 2015-05-10 8:03 AM, TexasRF--- via TowerTalk wrote:
> Bruce, to add another piece to your puzzle: Using a 1.5" mast sounds like
> you have a 25AG or 20AG top section that was intended for use with a 1.25"
> mast. These top sections are made with a top tube about 1.7" i.d. and a
> reducing collar welded to the end of the tube to make a 1.25" mast fit. The
> 25AG and 20AG tops were made to fit a small rotator for tv use.
>
> Many of these top sections are around that have the collar removed to allow
> use of a 1.66" o.d. water pipe mast.
>
> I have not seen one for ages and don't recall the exact rotator mounting
> arrangements. They likely are different from the current 25AG2 design.
>
> 73,
> Gerald K5GW
>
>
>
>
>
>
> In a message dated 5/10/2015 6:24:52 A.M. Central Daylight Time,
> bcarling at cfl.rr.com writes:
>
> 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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>>> TowerTalk at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>>
>> --
>>
>> 73
>>
>> Roger (K8RI)
>>
>>
>> ---
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