Greetings,
I'm a little new at this but have done some research on the subject. I have a
~65 free standing tower where the
mast is supported at the top, and the rotator is installed at the bottom.
Advantages as I determined:
1. Don't need to climb tower to adjust/repair rotator.
2. Wind/torque load is transferred to the bottom of the tower where it is much
stiffer and stouter and NOT the top of
the tower where it has less circumference, and more prone to torque failure.
3. Vertical load remains balanced throughout the tower with out the torque of
the rotator at the top.
Being thrifty on materials, I used some 1.5" pipe in the middle of the
assembly, with 2" pipe both at the top and the
bottom where it attached to the rotator. I also have 3 thrust bearings (not
including the top bearing) between the top
and the rotator.
Yes... it does exhibit some extra "twisting", but this has not caused any
problems, and in fact provides some cushion
to any weather events that might otherwise cause failures in other parts of the
tower. (A spring... can you imagine
the frame in a vehicle if no springs were installed and driven over a rough
road?)
Anyway... that's my two bits, and so far seems to meet the design criteria that
I had.
... 73
Rob
VE6TR
On Fri, 20 Jan 2006 09:43:15 -0600, Stan Stockton wrote:
>Bill,
>
>Thanks to you and to all the others who responded to my request for
>information. I am glad I asked for information and did not do something
>stupid that was sure to not be a good situation.
>
>It is clear to me that if I were to do this, I need a diameter of about 4
>inches with about 12 inches of circumference in order to not have a little
>twist translate into a lot of antenna movement. A quarter inch of twist in
>both directions with a 1.90" mast would indicate a total movement of the
>antenna of 30 degrees.
>
>Given that the mast would have to be large, I would use schedule 40 aluminum
>pipe about 4 inches in OD but will probably not do it unless I run into a
>scrap deal on the pipe. Regarding the welding process, I am sure that a
>plate, perhaps about 3/8" thick, 6 inches wide and 2 foot long at each joint
>with a few heavy duty muffler clamps would hold it. You could even pin it
>for extra insurance. Painting a perfectly straight line on the entire
>length of the pipe would give visual confirmation as to whether it had ever
>slipped.
>
>3.5 inch schedule 40 aluminum pipe would be 63 pounds per 20 foot length.
>If I had a large enough hold in the top of the tower, I don't think I would
>have a problem dropping them through the top.
>
>Mounting the rotator independent of the tower would take the torque off the
>tower and if a thrust bearing could also be independent of the tower there
>would be no weight on the tower itself from the mast and antenna.
>
>Sounds like a lot of work and perhaps I will not do it but still considering
>the possibility.
>
>Stan, K5GO
>
>
>----- Original Message -----
>From: "Wolfert, William R." <WWolfert@columbuspolice.org>
>To: <stan@aqity.org>
>Sent: Friday, January 20, 2006 7:40 AM
>Subject: RE: [TowerTalk] Rotator at bottom of tower
>
>
>> Stan
>> I'm not an engineer but I agree with the other TT'ers that indicate the
>> 1.5"
>> pipe is too flimsy to handle the torque to which it will be exposed. You
>> didn't say what type of tower you have, but did you consider how you would
>> get long sections of pipe into the center of the tower, unless you plan to
>> use a crane. I have AB-105 tower, which bolts together and I had
>> considered
>> inserting a piece of 3" about 21' long to use as a drive pipe (from a prop
>> pitch) to turn 3 separate antennas on side mounts. I pictured unbolting
>> enough side braces to slip the pipe inside. OK that would work. THEN... I
>> pictured myself on the tower trying to get the pipe into the hole I made
>> (I
>> do all my antenna/tower work by myself- as do many TT'ers I've come to
>> learn- great encouragement!) and realized this would be a mechanically
>> difficult venture. And that's with tower that I could make a much larger
>> "hole" in by unbolting the braces. Even if you have help, really picture
>> you
>> doing the task, maneuvering a (very) heavy piece of pipe from one end and
>> putting it into a very small space with lots of little hands to grab it
>> (tower bracing). And that is just one piece. You mentioned you need 105'!
>> Once the pieces are inside the tower, they then need to be connected
>> (welded) together! I think this is not a small task at all. Good luck with
>> whatever you decide and if you go for it, be safe my friend.
>>
>> 73's Bill WR8K
>>
>> -----Original Message-----
>> From: Stan Stockton [mailto:k5go@cox.net]
>> Sent: Wednesday, January 18, 2006 7:55 PM
>> To: towertalk@contesting.com
>> Subject: [TowerTalk] Rotator at bottom of tower
>>
>> I am "considering" the possibility of running 105 feet of pipe extending
>> the
>> existing mast to near ground level and mounting the rotator at that
>> location. The antenna is 20M5L48. I have to take the rotator down
>> because
>> of a maintenance issue anyway and thought that in the long run it might be
>> nice to have the rotator low to the ground.
>>
>> The plan would be to use 1.5" Schedule 40 pipe (1.90" OD), leave the two
>> thrust bearings that are located at the top of the tower and down about 6
>> foot, add another thrust bearing about 10 feet above the rotator and have
>> about 3 or 4 other brackets with UV inhibited PVC bearings to center the
>> mast from about 20 feet to about 110 feet.
>>
>> If any of you have done something similar, I would appreciate knowing the
>> pros and cons of such a plan.
>>
>> Thanks...Stan, K5GO
>>
>> _______________________________________________
>>
>>
>>
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>
>
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