[TowerTalk] Swing Gate Mounts

Wed Feb 1 00:50:23 EST 2023

I have made a few over the years.  I never did anything more than three pieces of angle across one face of the tower - one for the rotator mounted on a plate bolted to the horizontal part of the angle, pretty close to directly off and as close as possible to a leg, and the other two each with a couple muffler clamps on the vertical faces holding short pieces of 2 inch gray conduit for “bearings”.  In between those bearings the “gate” was just 2 inch tubing that was horizontal - trussed as necessary.

 I would  not do this for a large 40m antenna but I never had an issue with 20, 15 or 10m antennas on booms up to 25 feet or a 2L shorty 40 antenna.  I probably never had anything that weighed more than a hundred pounds.

Of course I’m not a PE and do know that a PE wouldn’t approve of a lot of stuff I have done based on what I was pretty sure would be just fine. 

The problem is you need a huge gap between elements to get the most rotation unless you are using 25G.  You pretty much need the dimension across one face plus the distance from the leg to the center of the rotator X 2.  It can be difficult to design one of those tribanders that has a dozen elements in a span of 24 feet if you are using 45 or 55G.

73…Stan, K5GO

Sent from my iPhone

> On Jan 30, 2023, at 10:08 PM, Steve Maki <lists at oakcom.org> wrote:
> I was only talking about the gate itself. Of course the wider the tower face, the longer the gate needs to be. And the more thought one needs to put into the element spacing and boom-to-mast clamp location on the boom, especially for 10M yagis. But it's a very good solution for many scenarios.
> 
> -73, Steve K8LX
> 
> On 1/30/2023 8:03 PM, Grant Saviers wrote:
>> I'm not sure about the swing.  Best to draw it out on the exact tower dimensions.  Also how the elements clear.
>> Grant KZ1W
>> On 1/30/2023 15:23, Steve Maki wrote:
>>> Yes - the X configured bracing, which gets all three legs involved, is how we made all our swing gate mounts and collars in the late 90's. That puts the rotor straight off the leg, which automatically gets you 300° rotation, right?
>>> -Steve K8LX
>>> On 1/30/2023 6:08 PM, Grant Saviers wrote:
>>>> Might be better as a new topic "swing arm mounts"
>>>> Some expert advice I got was to use crossed A36 angle steel (2x2x1/4 or 1.5x1.5x3/16) U-bolted to all three legs and mount the rotator close to the tower on a 3/16 plate bolted in the V in the outside gap.
>>>> Repeat for the top bearing, xx feet above the rotator.  Could use a stock "thrust" bearing or a simple UHMW block with all the load on the rotator.
>>>> The swing arms were about 33" long mounted the the mast, which was going to be 1-7/8" x 0.188" 1026 DOM.  The mast was to be 13ft between mounts so able to mount 2 yagis.  A triangular brace mast to arm and a stub mast welded on the arm to mount the antenna with a stock mast-boom clamp.  Of course YMMV.
>>>> It's important to have all three legs capture the loading.
>>>> Ideally get it all hot dip galvanized or do a good pant job.
>>>> And find a PE to recommend a design for the planned yagis.
>>>> Grant KZ1W
>>>> On 1/30/2023 11:32, Steve Maki wrote:
>>>>> On 1/30/2023 2:23 PM, Lux, Jim wrote:
>>>>>> On 1/30/23 11:10 AM, Steve Maki wrote:
>>>>>>> On 1/30/2023 1:48 PM, Lux, Jim wrote:
>>>>>>>> On 1/30/23 9:46 AM, Grant Saviers wrote:
>>>>>>>>> I agree side mount + swing arm is a good option.
>>>>>>>>> Although my 7 K0XG R65 rings have worked great minus one motor failure, I would do side mounts for future (unlikely) towers.
>>>>>>>>> The advantages of side mounts are lower cost & weight, using standard rotators, and if desired with multiple beams on a long mast between rotator and top support.
>>>>>>>>> The side mount disadvantages are less rotation (but still can get ~250*), some offset load on the tower (use 6 guys or star brackets), and easily fabricated or purchased unique parts, although you/PE need a design.
>>>>>>>>> I think the updated Orion 2800 is a better choice than the Yaesu for very big beams.
>>>>>>>> I've been thinking about this, and I wonder if there were some "not too complex" scheme with an extra hinge point on the arm that would get you 360 degrees.  Not that I would build such a thing (would that I had room for it) - but I was thinking if you had an arm that is the length of a "face" of the tower, and some sort of offset crank linkage, you could get 360 of rotation from 240 degrees (or less) of movement from the primary arm.   My mind's eye has this as like a "wrist" that reaches around the tower. Yeah, you'd have the mass of the antenna as a cantilever load, which would put a bending moment on the tower.
>>>>>>> A swing arm where the rotor is mounted straight off a tower leg is good for 300° easy. That's plenty as long as you have another antenna to cover the dead zone.
>>>>>> Oh yeah, I figured that.. I was just contemplating "clever mechanical solutions" - The swing arm is actually a nice solution in general - simple, uses off the shelf stuff, can be added after the tower is up, etc.
>>>>>> It's like the hinge plates for mounting an antenna on a tower/mast that pivots from horizontal to vertical - a simple clever solution.
>>>>>> Of course, the other solution is to mount two (or three) Yagis and a combining network to phase them (or just switch). <grin>
>>>>> Yep, I was trying to picture your idea. Back when linear actuators were cheap (used in the satellite dish industry) I put some time into thinking about a way to use one or two to turn a large yagi on a swing gate. It never got past day dreaming and a little pencil scratching.
>>>>> -Steve K8LX
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