Flat beam w/ imax 2000 on top

[1502gulfcoastMS]

Hello I was not able to find a thread about this here so I'm going to start one. If this has already been gone over if you could point me in the right direction that would be great.

I'm about to mount a sirio 4 (sy4 ) element beam on the flat side. I'd like to mount my imax 2000 right above the beam on the same pipe. How high above beam will the feed point for the imax need to go? I'm using a very inexpensive rotor as this is my 1st tower beam set up. The rotor is rated to handle the weight of the beam but not by much. I'd like to keep the pipe above a short as possible. The feed pointo for the beam will be at either 27' or 36'

The tower will be on a home brew hinge plate which will make it easy to bring up and down when that rotor goes out

Any extra advise is more than welcome

1502
TomTom
73

 

[M0GVZ]

I'm about to mount a sirio 4 (sy4 ) element beam on the flat side. I'd like to mount my imax 2000 right above the beam on the same pipe. How high above beam will the feed point for the imax need to go? I'm using a very inexpensive rotor as this is my 1st tower beam set up. The rotor is rated to handle the weight of the beam but not by much. I'd like to keep the pipe above a short as possible.

Any height you want but here's the problem. Putting a vertical on the same pipe as a beam puts massive lateral strain on a rotator when the wind blows which will cause damage to the rotator even though the overall weight is still well within capacity.

What you need to do is to put a rotator cage on top of the tower. The rotator bolts to a plate at the bottom and the pipe feeds through the middle of the cage, going through a hole at the top which has a bearing in it. What this does is remove all the lateral loading from the rotator and transfers it to the tower instead. It also takes the weight off it as well so it'll turn easier and last longer. The pipe can be just long enough to bolt everything on. The vertical antenna will have little effect on the horizontal beam.

 

[1502gulfcoastMS]

I would have never thought of that. I will for sure have to make something for my rotor like that. Looks like that one would turn the house. I was so close to throwing that up this week end. Looks like I still have some work to do.

As far as the height. Would the beam work as a ground plane with that I max?

 

[Captain Kilowatt]

What do you plan to use for a tower? Most decent towers have rotator plates installed anyway. Usually the top section is different and has a rotator plate installed as well as a top plate to mount a bearing so there is no need to make up a rotator cage like shown above. Even the old Radio Shack towers had a rotator shelf and the top tapered such that it would relieve sideways stresses on the rotator.

 

[2RT307]

The Sirio has a pretty light wind load, but be prepared (I see you're on the gulf coast) for winds to beat the brake. Not a really big deal, since you can spin it to the stop, and reset your dial. I always used to turn my Maco 4 element so that it was against the stop during high winds. Was kind of in the same boat, my rotor wasn't quite up to snuff for Texas winds. You WILL hear things on the beam that your buddies on verticals don't. I had an S-9 on a fella in South Dakota for 30 minutes, and my friends thought I was ghost talking.

73,
Brett

 

[1502gulfcoastMS]

What do you plan to use for a tower? Most decent towers have rotator plates installed anyway. Usually the top section is different and has a rotator plate installed as well as a top plate to mount a bearing so there is no need to make up a rotator cage like shown above. Even the old Radio Shack towers had a rotator shelf and the top tapered such that it would relieve sideways stresses on the rotator.

I think it's a rohn 25g. Not 100% sure. There is no bearing nor rotor plate. Where I work I will be able to make anything I need. The type of rotor I have is cheap one from radio shack. It's made to mount to a pole. I'll just weld a pole to the plate and attach to it. I will also make another plate for up grading in the future. Attached is a picture of what I have. This is not mine, just the same type. I have 5 10' pieces and a 10' top.

Thanks for all this great advise. Not many beams here on the MSGC.

 

[Captain Kilowatt]

OK that top section is meant to have the mast sleeve inside it to take the sideways stress off the rotator. Most people use a mast just large enough to rotate freely inside it and use a dab of grease. There is a rotator plate available from Rohn for that tower or you can make a simple one yourself.It mounts to the tower with three simple U-bolts. You could make one with a pipe attached to accept your rotator.

https://www.google.ca/search?q=rohn...2&ved=0CBsQsARqFQoTCNi7-vakickCFcodHgodkmgIRQ

With some careful measurements you could build something like the Rohn Rotor Post like below. It bolts to a leg inside the tower and aligns the rotor to the top center sleeve.

http://www.3starinc.com/rohn_25g_tower_antenna_rotor_post_r-rp25g.html