Rotor Size for a Wilson and TH6

[KC9LKE]

With the sunspots and 20M AM on the rise its time to start poking around for a rotor that will work FB with my tower and antenna. The tower is a 55’ Wilson and the antenna is a HyGain TH6DX. No problem finding the wind load etc for the TH6 but no specs for the Wilson tower. Just seems like a lot more mass to rotate than a mast mounted rotor so I am wondering about the size of the rotor needed for the job. I would love to go the prop pitch motor route but right now I have to be realistic with my time. So I’m looking for model #’s that would work well. Any suggestions?

Thanks as always..

Ted / KC9LKE

[K1JJ]

Ted,

Rotators have always been a weak point and trouble for most users. The only solution is to get something rated several times greater for the job. You definately need a rotator that gets mounted on a plate inside the tower.

The top-of-the-line Yaesu rotator has good reports as well as the M2 rotator and box.  Go with something that is rated for a full size 3el 40M Yagi and you should be OK. I think the M2 will even turn a 75M Yagi, so you should be in good shape.

I have a prop pitch here and know several others with them. It seems water seeps down into the gearbox and does damage. They were designed to be enclosed and in a horizontal position, so if used, take extradinary measures to keep them dry when exposed for ham use.  I used a rubber boot that straddled the mast covering the rotator with some success.

T

[Jim, W5JO]

Does anyone have any experience with Alpha-Spid?  It seems to be a very good product, but I haven't seen any peronal comments from anyone I know that will rate the product fairly.

[Pete, WA2CWA]

In order to do the job correctly, you need info on the tower. You can put the best rotor you can find on the tower, but if the tower can't handle the wind load of the antenna(s), it's all a waste of time. Is the tower crank-up, free-standing, requires guys, is it tubular, or triangular, how many sections, if triangular, the bottom section dimensions, how is the tower mounted to the earth.


Jim:
I've had an Alpha-Spid rotor since about 2004. Works great with worm drive, 1 degree positioning, self-braking action with double worm drive reduction. My Tailtwister can only get about 6 degree positioning accuracy, manual brake, and lots of high wind slop in the mechanism.

[K1JJ]

Another great rotator, maybe one of the best, is the European made, "Big Boy". They have a big and medium  IIRC.  Do a search on that name. I know someone who replaced their prop pitches with these and were happy.

As Pete said, the tower specs are important. Though, Ted, if you were considering a prop pitch, I figure you have a very robust tower there.

Even a well-guyed Rohn 45 can fail from torque. I know a guy who had a 75M rotary Yagi turned with a prop pitch. I climbed to the top and saw broken welds on the zig-zag bars near the top.  He probably should have used large triangular torque arms for the job. (six point star guying per level with a pier pin) Two of my Rohn 45's use them here.

T

[Fred k2dx]

Mounting the rotor lower on the tower is desirable. The pipe between the rotor and thrust bearing at the tower top will absorb torque, like a torsion bar.

The torque is a major consideration that hams tend to overlook, the square foot windload is a starting point. The longer the antenna boom the more twisting force you have, think of it as a lever multiplying force.

The TH6 isn't a huge load, even a properly installed tailtwister should be ok.

[KC9LKE]

ooops a case of writing to fast, or “you don’t know what I‘m thinking?”

Thanks for the input Tom, Pete, Fred.

Tom: Got ya on rotors giving trouble. The rotor on this setup was removed and was on a bench in pieces the last I saw it. I was long gone when I came back to take the tower down.
 
Pete your right this job should be done correctly. I was in a hurry and misstated myself.

It’s a 50’– 55’ crank up, fold over, tubular. The rotor mounts at ground level and the whole mast rotates. I have the specs at home for the tower BUT IIRC they don’t give any factor to add in for the “mast” when choosing a rotor. That’s what I worried about. What Fred said while I was writing this.

Ok so let’s back this up. Tom I have seen the pictures of your tower, or one of them. You rotate the whole tower? Did you have to account for this or is it negligible compared to the beams themselves? (Read moment)

Thanks
Ted / KC9LKE

[Pete, WA2CWA]

The Wilson tubular towers are similar, if not identical, to the U.S. Tower "MA" tubular version.
http://www.ustower.com/uploads/pdf_file/HAM%20CATALOG.pdf

[K1JJ]

Hi Ted,

Since your rotator is at ground level there is negligible torque on the tower.  Just make sure your thrust bearings are well greased. This is a good thing since it is a self-supporting fold-over.  The biggest factor will be ice loading and winds on the antenna that will tend to buckle the tower over.

None of my towers rotate. In fact all of my arrays are fixed in various directions and switchable via phasing or separate antenna directions.  I use rotatable side arms on the 20M and 10M stacks, but they are turned via ropes that are anchored to the ground. (330 degree coverage)

I wonder what diameter and wall size your 60' mast is?  I'll bet it will twist at least 30 degrees in high winds due to torque.  As Fred said, this flexibility will lessen the shock on the rotator by acting like a cushion. Some guys even mount their rotators on rubber pads, but in your case, your are all set with the long mast. That's a good way to maintain rotators - keep them on the ground...

T

[W2VW]

The torque on those tubular towers has to be handled by a keyway and metal strip.

There are light and heavy duty versions.

IIRC the bottom section is about 8" O.D. on the heavy types. Those can take some windload.

[K1JJ]

OK, I see - this Wilson is a "tubular tower" not a lattice-triangular  Rohn 45 type. For some reason I thought "tubular" referred to the type of material used to build it, like the legs on a Rohn. This tower is more like a set of telescoping pipes.

My previous post applies to lattice only... never mind!  

T

[KC9LKE]

Thanks for the replies.

The US towers info will come in handy, it’s a good start I’ll give them a call.
Tom, sorry about the mix-up even after two post I still didn’t give all the info.
Best Regards
Ted / KC9LKE