V/H Directional Beam Installation

[Kikker]

I've done a little research and can't find an answer to my question.

I'm in the process of putting up a 5 element vertical/horizontal beam antenna using a 2" diameter steel mast.

What are the recommendation on the height of the antenna above the top of a Rohn 25G tower? Are there any performance issues or concerns with the proximity of the lower vertical elements with the tower if the elements extend below the top of the tower when there is approximately 4' from the driven element to the tower.

The reason I'm asking is that I'm using a Hy-Gain T2X Tailtwister rotor mounted on top of the tower and the manufacturer recommends a 2' long mast.

 

[wavrider]

IMO I prefer to use a long enough mast pipe so that the elements of the yagi clear the top of the tower.

 

[M0GVZ]

For a vertically polarised one you need a lot more clearance. You also want to be using a non-metallic pole unless stated otherwise it interacts with the antenna and seriously stuffs things up.

If in doubt contact the antenna manufacturer.

 

[W5LZ]

With your rotor mounted where it is, you're limited by it's requirements, 2 feet. If you could move the rotor to inside that tower you could extend the mast to almost any length, depending on the limits of the mast. Those min/max limits are there for a reason, I think I'd pay attention to them.
- 'Doc

 

[w9cll]

Yes tower mount the rotor and any length mast will work.

 

[Captain Kilowatt]

Been there done that with a 4 element V/H. About three feet of the vertical elements were extending below the top of the tower and it did not affect a thing at all. On VHF it's a different story but for11m there is no issue. Tower mounted rotators are the best however if you can mount rhe rotator right under the antenna and use a longer pipe UNDER the rotator it would be better than a long pipe above it. Don't sweat a few feet below the tower top. As I said mine was and I worked all over the world and had a decent SWR and pattern to boot.

 

[Kikker]

Is there such a thing as a 2" O.D. non-metallic tubing that's strong enough to support a 41 lb. antenna? I suppose fiberglass for example. Does anyone else use anything other than steel mast material?

The steel 2" O.D. mast I have weighs about 35 lbs. by itself.

 

[Captain Kilowatt]

You will need a metal mast. On HF even at 11m the issue is minimal. On VHF and UHF it becomes almost paramount that you use a non-metallic mast for proper performance. Having said that i have run an 11 element 2m yagi vertical with a metal mast and the SWR was good and the pattern was still pretty good. Maybe not ideal but good enough.

 

[Kikker]

The issue has been so far that the 10' steel mast has put a pretty good load on the rotor while trying to get it raised.

 

[wavrider]

thrust bearing
use one and take the load off the rotor

 

[Captain Kilowatt]

You have ten feet of mast ABOVE the rotator?! That is a recipe for disaster my friend and a rather expensive one at that unless the mast goes thru a thrust bearing above the rotator to take the sideways bending forces off tbe rotator. My installation will have 17 feet above the rotator but my rotator is mounted inside the tower on a metal plate and I have a thrust bearing at the top of the tower that the mast goes thru.

 

[Kikker]

Yeap, I've come to that conclusion also. I'm going to have to stop listening to all of the advice I have been getting. I'm changing the top section of the tower to except a thrust bearing and mount the rotor inside of the tower. Unfortunately the Hy-Gain Tailtwister will not fit inside of the tower and I'm having to buy another rotor.

Anyone want to buy a recently rebuilt Tailtwister with a brand new Hy-Gain MSHD Lower Mast Support on it?

 

[M0GVZ]

Don't worry - you won't have been the first one to make that mistake and it sounds like you know plenty who have. At least you've found out now before it becomes more expensive.

 

[Road Squawker]

... I'm changing the top section of the tower to except a thrust bearing and mount the rotor inside of the tower. Unfortunately the Hy-Gain Tailtwister will not fit inside of the tower and I'm having to buy another rotor...

if you can find a Rohn BAS25G top section (which has a thrust bearing plate at top) the TX2 rotor will fit inside without any tower modifications because the cross piece is not in the way.

good luck