Rotator at Top or Bottom of Mast

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chrissim

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I'm trying to prepare for the arrival of a hexbeam. I'll be getting a ROHN 9H50 (about 30 ft. high) telescoping mast to support the hex. I'm uncertain if I should place the rotator at the top or bottom. I would have to get something along the lines of a Yaesu G 450 if I intend to rotate the entire mast. I could use a cheap Radio Shack rotator if I place it at the antenna, but that would increase the chances of the mast succumbing to inclement weather when once considers the additional weight of the rotator at the top.

I am assuming that the guy rings on the ROHN freely turn so that the mast can be rotated.

The hex is about 20 to 25 lbs.

Please provide opinions.

Thank you.
 

mmckenna

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There are is some pretty good info here:
http://k4kio.com/files/Push_up_mast_details.pdf

Personally, it seems the push up masts are a little light weight for an antenna this size, and the linked to PDF seems to even suggest that. Adding a rotor to the top isn't going to help that situation, although it would save money. Running things at the edge of their design envelope like this creates these sort of limitations. Looking at that PDF suggests that it's been done both ways. I think it would come down to how much risk you are willing to accept. A good gust of wind could destroy your antenna, and anything in it's path. Investing in either a better support structure, or putting the rotor at the bottom, might be the lesser of two evils. Personally I'd put up something along the lines of a Rohn 20g or 25g, but that isn't the question you are asking.

Seems like rotor at the base is a better option.
 

WA0CBW

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I wouldn't put the rotor at the bottom of the push up mast. The guy rings do rotate on the mast but add a great deal of downward pressure when the guy wires are used. It takes a bigger rotor when mounted at the bottom. This puts a lot of weight and torque on the rotor. As mmcenna said a better support structure for that antenna would be money well spent.
 

prcguy

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I agree, a rotor inside a tower with a thrust bearing at the top is the best way to go and a guyed push up mast on top of a rotor is not a good idea. The guy rings would need the equivalent of thrust bearings and if they ever snagged it would create a huge problem.
prcguy

I wouldn't put the rotor at the bottom of the push up mast. The guy rings do rotate on the mast but add a great deal of downward pressure when the guy wires are used. It takes a bigger rotor when mounted at the bottom. This puts a lot of weight and torque on the rotor. As mmcenna said a better support structure for that antenna would be money well spent.
 

chrissim

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Thank you for the replies and suggestions. Unfortunately, I live in a HOA restricted neighborhood, which is the appeal of this antenna and a push up mast.

From what I have read, and what the K4KIO page suggests, is that push up masts are commonly used for such configurations. I spoke with a very knowledgeable online retailer (whose ratings for customer service are excellent), and they suggested the RH950. I specifically mentioned weight and was assured that this particular mast would be fine providing it is guyed. I'll have to check into the gauge of the mast,it very well could be smaller diameter than I should use. Really, I don't know what else to do in my situation.

I agree that a rotor at the bottom could present some problems. My initial inclination was to place the rotator at the top, but as I mentioned I am concerned about the additional weight.

This certainly seems to be a conundrum. There simply is no way I could get away with some type of tower - they'd run me out of the neighborhood.

Thanks again for the replies.
 

n5ims

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Just to help show you that a push-up pole isn't less visible than a tower I'll pass this along. I used to have a small VHF beam and rotor on a 30' push-up pole. A few doors down, a neighbor had a huge TV antenna on a 60'+ Rohn 25 tower. Our house was the one known as the "house with the tower" while nobody even noticed the neighbor's.

This was due to two main things. My tower was guyed (as all push-up masts must be) and had no large trees behind it. His was self supporting (no guys) and had some nice tall trees behind it. Although my antenna was smaller and tower much shorter it was visible from most every angle. His was totally hidden by the trees when viewed from the street behind his house and from the front, the dark background of leaves made the tower very hard to see.
 

NC4DK

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Final Verdicy

What was the final result of the installation. I have a K4KIO hexbeam I intend to install on a 9H50 mast with a bottom mounted Ham IV. My plan is to place a second pipe in the ground parallel to the mast. This will allow a thrust bearing to be installed 8-10 feet up. Two sets of guys will cover the remainder. I am looking for ideas on some type of bearing assembly for the upper guys. I'll probably only go up about 30 feet. I have had good results with 30 foot beams on these bands during Field Day and Leo, K4KIO, advised that his was only up about 30 feet. Would like to hear the final configuration on this system as well as suggestions for guy wire bearings.
 

chrissim

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What was the final result of the installation. I have a K4KIO hexbeam I intend to install on a 9H50 mast with a bottom mounted Ham IV. My plan is to place a second pipe in the ground parallel to the mast. This will allow a thrust bearing to be installed 8-10 feet up. Two sets of guys will cover the remainder. I am looking for ideas on some type of bearing assembly for the upper guys. I'll probably only go up about 30 feet. I have had good results with 30 foot beams on these bands during Field Day and Leo, K4KIO, advised that his was only up about 30 feet. Would like to hear the final configuration on this system as well as suggestions for guy wire bearings.
A blast from the past! The KIO worked remarkably well at 40 feet on the push up mast. In the short time I had it, I added roughly 170 new entities, many of which I couldn't hear before the installation.

I put the G450A at the top of the mast and had three sets of guy ropes. One set of three at the top just below the rotor, and the two other sets worked their way down.

My wife and I stood atop two ladders as I pushed the mast up and she locked the mast in place. I then drilled a hole whenever I reached the stopping point of a section and inserted a stainless steel bolt and nut arrangement to secure it further. I used the preexisting cotter pin holes to insert the bolt, just drilled them a bit larger. Both my wife and I are pretty small and lightweight (5'8 140 lbs) and it really wasn't that difficult. I was concerned that it would be top heavy, but it stayed extremely stable despite numerous storms and heavy winds. I used Wireman 3/16" UV resistant Dacron 770 lb break strength for guy lines.

I initially thought of placing the rotor at the bottom, but found it difficult to source the parts I wanted. If you'd like, send me a private message with your phone (or I can send you mine) and we'll discuss it further. Regardless, good luck with your installation. I found the hex to be true to its eham rating.
 

wb6uqa

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Rotor at the top

I have a rohn 5 section with a 450a and a 6 band hex at the top. I would guy every section in 3 or 4 places. If you plan to lift this up and down every day, forget it.
 
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