HyGain vertical vs Yagi over metal roof...which one to use?

[VE7 Kilohertz]

Hi guys,

In my last week before it really gets nasty here, I want to put up an antenna for the 20-10M bands. I have already assembled a TH5DX, 6 element compact triband and a new in the box AVT18-WB vertical. If I go with the yagi, it will be on a 40' tower strapped to the side of my shop, which has a tin roof and is 16' above ground at the apex. I would have to run 100' of rotor cable to the shack. If I go with the vertical, no rotor, it would mount in the middle of the roof and use the roof as the counterpoise, properly bonded of course. Easy peezy.

I would mainly be chasing DX over the pole, or to ZL and JA land. A few USA friends on 20M but mainly DX. I know the vertical has no gain, but has a nice low TO angle. The yagi has gain, and F/B ratio but may not be that great with half of it sitting over a metal roof.

So, let me know your thoughts, the pros/cons I may not have considered.

thanks

Paul

[W3GMS]

Paul,

Go with the Yagi.  It will give you rejection to cut down on the QRM.  They sometimes are quieter than verticals but that depends on your QTH.  I had a TH-6DXX up for many years and it worked very well for what I wanted to do.  Ran legal limit and stations heard me very well.  Mine was up 60' and I was pleased with the results. 

Since you have a vertical as well, why not put that up also.  If your going to work AM round tables on those bands, its sometimes nice to have the capability of switching over to an omni directional antenna.   If you just going to chase DX then I would use the beam.   

Joe, GMS 

[VE7 Kilohertz]

Thanks Joe,

I should add a bit more info to the story. This is going to be an interim antenna, something quick and easy to get me going with some aluminum, until I can get my 70' Samson freestanding tower up in the next year or so, topped with a KLM KT-34XA.    Who, knows it may be longer....   However, if the TH5DX works well, I may not go with the big monster.  I was just concerned that the yagi at 40' with a tin roof sitting 24' below it, might not perform that well.

cheers

Paul

[WBear2GCR]

I'd expect that it will work well enough, especially if the tin roof can be grounded.

Just a guess on the grounding part.

It may tune a bit differently than it would at 60' free air, meaning that you might have to adjust the length of the elements from what is expected, and/or the SWR may vary a little along with the pattern as you rotate it. But it will play.

                        _-_-bear

[N8ETQ]

Hey Paul,

      Sounds like you could just leave the Vert. on the roof anyway.
From a pure "Labor" standpoint I would go with the Vert. on the roof.
I have often wondered about elevating a Vertical Vs. the compromised
Ground situation most of us would run into by doing that. Your
in a good situation. I always liked my Vert. An old "Butternut"
ground mounted. The Yagi will come...

GL

/Dan

Hi guys,



I would mainly be chasing DX over the pole, or to ZL and JA land. A few USA friends on 20M but mainly DX. I know the vertical has no gain, but has a nice low TO angle. The yagi has gain, and F/B ratio but may not be that great with half of it sitting over a metal roof.

So, let me know your thoughts, the pros/cons I may not have considered.

thanks

Paul

[Jim, W5JO]

Putting a vertical over a metal roof may gain you something but probably won't.  If you will be sure all the metal  panels of the roof are bonded together, it will work well.  If they are not then you can have an inefficient antenna.  If you put it there then add at least 4 elevated radials for each band you will have a better antenna just try to keep them at 90 degrees horizontal from the antenna and spaced 90 degrees apart.  

The beam at 40 ft. will be more efficient if the roof is not in good condition for RF.  The vertical will work and it will be a bit better than the same vertical over poor ground.

[VE7 Kilohertz]

So I built the antenna in the living room this AM and then moved it outside. Worked in the shop, insulating and getting ready for the wood stove, then took a break and built the vertical stand, and got the antenna all mounted on the roof...then it started to snow..so now I will have to wait to get the coax connected then I can run some tests.  I built the mount so it will hold 2 large deep cycle batteries for weight (dead and drained of acid), on either side of the peak.

Yeah!

Paul

[N8AFT]

One of the few contacts I've ever had with a ham using a trap vertical had it mounted and bonded to a metal roof of a high school...Go For It.

[WBear2GCR]

I'm not sure the batts will hold that on the roof.

If the mount was say 6-8' on either side of the roof, I'd say you're likely ok in the event of a big wind. I know the wind load for a vertical is relatively low, but it is a big lever...

The resistance to tipping in the direction along the ridge of the roof is very low with that mount. It needs to be much wider or have outriggers.

I'd LAG it into the roof joists (or whatever those are called.) with such a short mount.

I've had a 4' diameter spun aluminum sat dish on a roof for many years, but it has a two level mount (the roof has a low/high level, 6' difference in height) and that uses very heavy wide web angle iron each leg of which is about 5 ft and lagged into the joists on two levels. I know that's a heap more wind load, but the distance between the dish and the upper roof is not much, like total height 6' maybe  a tad less, so there is less effective force than on a tall pole... I'm concerned about the height of the vertical making for a very good strong lever.

                    _-_-bear