tin roof & base antenna questions

[Prime Number]

I’m thinking of putting in an A-99 either on or near my tin-roofed shed. The roof is 50’ x 25’, with the ridge of the roof running longways; top of the ridge is about 20’ above ground. The roofing metal itself is unpainted galvalume-coated steel -- about as conductive as a roof can get. Due to zoning/neighbors, I can’t go much higher than 40’-50’ with the entire height, so putting up a mega-mast to get well above and away from the roof isn’t an option here.

Here are the questions:

- Is it worth it to use the roof as a ground plane?

- Or just avoid that big reflector and its unknown properties altogether by putting up a mast some distance away?

- If the roof can work as a ground plane, is it OK to mount the antenna at one end, or would it be significantly better to mount it in the middle?

- Will mounting the antenna at one end give any kind of beam effect?

- Any thoughts on grounding the roof to the antenna system?

Again, I can’t put up a mast that would be significantly higher than the roof anyway, so I expect antenna performance will be affected by the roof no matter what I do. It would be very cool though to turn this complication into something good! Any voices of experience will be much appreciated.

 

[gamegetter]

first I have never attempted such an install where you would use such a roof as a counterpoise. How would you mount to the roof for such a groundplane/counter poise?

I don't believe that using it as ground plane would be possible and if so there is the possibility that it is too much counter poise.

More than likely what you would encounter would be reflect from said roof and interference from an object in the antennas near field.

Alot of times each person's install can and will be different based on many variables and the only way to find out for sure is to experiment or tinker with the set up. Alot of us have spent a life time trying to figure out which antenna may or may not work in a particular set up only to find out that in a similar set up it does not work for someone else.

Maybe others can share some experience and see if you can get some help or ideas. good luck and try to enjoy the hobby even though it can be challenging sometimes.

 

[W5LZ]

There's nothing wrong with using a metal roof as a "groundplane", as in mounting an antenna on top of one. Yes, it will have an affect on how that antenna performs. Just how it will affect it is really variable, but in general, it's just like having any kind of good "groundplane' under an antenna, sort of nice. It will affect the tuning of that antenna, you may have to adjust that tuning a bit to get thing 'right'. But then, you'd probably have to do that sort of thing no matter where you mounted it.
The practical aspects of mounting to that metal roof are probably more important that anything else, keeping the thing on there isn't always real simple. A nice firm 'footing'/mounting method is a very good idea. On that roof wouldn't be a good as a couple of hundred feet in the air, but then it's certainly better than under that roof, right? Give it a try.
- 'Doc

 

[HomerBB]

I would put it in the middle on a tripod of some sort. Perhaps putting a pipe up through the roof mounted to a rafter with a roof jack to seal from any weather.

Mounted at one end would likely cause some directionality in your pattern in the same way placing an antenna on the one end of a vehicle does.

 

[gamegetter]

i have to ask whether the a99 has enough counterpoise on it's own or whether the half wave really needs additional counterpoise.

 

[Prime Number]

Thanks for the answers folks. Looks like it boils down to "if you're going to do it, put the antenna in the middle." Putting it out at the back end of the shed would probably point the rudimentary beam toward Mexico, which is not exactly what I'm looking for. (And no, I am not going to mount the whole darned building on jacks so I can steer the beam! Though that would be pretty cool.)

i have to ask whether the a99 has enough counterpoise on it's own or whether the half wave really needs additional counterpoise.

I don't really think that it needs any more, but I'm going to have to deal with this tin roof one way or another -- as ground clutter or as a potential Good Thing -- and this is a good place to ask if anyone else had tried something similar.

Right now, I'm leaning toward just putting up a mast over in one corner of the yard, away from this roof so it can maybe be ignored, and moving on from there. Thanks again for all the replies from the pool of experience.

 

[XBUNCEX]

So.....how did it work out for you???

 

[Beetle]

If the roof is made up of several sheets of that "galvalume coated steel", it isn't necessarily "as conductive as a roof can get". At least at RF. I'd use some galvanized hardware and fasten things securely wherever one sheet of roofing overlaps another, and then seal the junctions well to keep them dry. Places where two metallic surfaces come into contact with only the force of gravity holding them together are potent sources of electrical noise, AND if there is another source of RF in the area, like a radio or tv broadcasting antenna, you could be causing mixing products up and down the spectrum. Google "rusty bolt interference" to see more.

 

[sdmahr]

Get a GOOD magnetic mount mobile antenna and stick it up there. I did that on top of a mobile home YEARS ago and it was one of the best antenna's I ever had set up.

 

[Oatmeal]

I'm running a Imax 2k here over top a tin roof.....the antenna is 9ft above the roof line and have no reflect or any swr problems, hope this helps...

 

[Tallman]

I would put it in the middle on a tripod of some sort.

I had a house in the boondocks with a tin roof and mounted a 5/8's wave dead center of it with a five foot tripod and ten feet of pipe. Got great signal reports from all over the place. I did do the station ground bit and it helped on the receive to reduce the noise from passing vehicles. Lots of noisy ignition on cars back then in 1974. Never had a problem with swr or tuning. I would not bother with trying to mount to any of the rafters if the roof is not mounted to solid boards add a piece of 2X6 to attach the footing of the tripod to.

 

[Heavy Metal]

I ran my i-max off a conner fence post( 8" post that's 8 foot tall and @5' out of ground ) to my pasture and only made it half of the whole antenna itself was above the roof top and did not clear any of the trees in back ect and could make conversations with England ect not a problem.

 

[Captain Kilowatt]

I ran my i-max off a conner fence post( 8" post that's 8 foot tall and @5' out of ground ) to my pasture and only made it half of the whole antenna itself was above the roof top and did not clear any of the trees in back ect and could make conversations with England ect not a problem.

I had a half wave dipole in my basement strung from the ceiling joists and made contacts with the UK and Florida but it was still a shitty antenna.

 

[wavrider]

I had a steel whip mounted on side of my truck bed and worked into UK on 10 meters with a Uniden HR 2510 doing 20 watts output Using RG8X coax.

Maybe it was due to me hauling some cow manure for garden fertilizer in the bed of the truck.

Guess that makes it a shitty contact.

 

[Road Squawker]

I had a half wave dipole in my basement strung from the ceiling joists and made contacts with the UK and Florida but it was still a shitty antenna.

I can tell ya stories about my Cantenna too