1/2 a dipole or ?

[KE7XD]

Any thoughts on shooting a straight wire out from the end ridge of a metal building.  I am in a temporary setting where one option is to run a coax to the peak of the roof.  What would happen if the coax shield is connected to the metal at that point?  Will the overall setup load like a vertical pushing against the metal as a ground plain, or maybe look like one half of a dipole pushing against the metal like it would if it were the other half of a dipole.    This is for a very temporary setup only.  (Metal building is 24 X 60 X 12 foot eves. )  Can I run a 60 to 65 foot wire out and use it multi band ( 10 to 80 M )?  It will be connected to an antenna tuner.    Does any of this make sense ? ?    Any thoughts ?

[KX5JT]

Any thoughts ?

Try it.

[W1FVB]

Probably, will act like a low hanging dipole, great for local contacts

Frits

[WU2D]

Frits,

Sounds like a nice portable setup and nothing wrong with a metal roof! The problem is the the 65 ft wire will look very high Z on 40M and your tuner will not help if it is at the rig down the coax.

Do you have a remote tuner? That would be the ticket.

However, If you bring a 65 ft wire AND a 33 ft wire out from the same feed separated slightly, you will be able to use it on 75, 40 and 15 with good effect from the simple coax tuner at the rig.

If your building is very high and you feed high and slope it down it at 45 degrees or so, you have just made a sloper and it will be directional in the direction it slopes away from the building.

Even low works. I had a buddy who worked a 65 footer against his mobile home at about 25 feet ht and it worked very nice for local 75M.


Mike WU2D

[KE7XD]

Thanks guys for the feedbacks.     No remote tuner, however a second wire sounds like would be a good idea.  The building height will be about 16 feet.  Because of a small shed and bushes, a sloper is a no go.    I like John's idea, just try it.

[KD0HUX]

 TRY IT NOTHING VENTURED NOTHING GAINED

[w5omr]

Thanks guys for the feedbacks.     No remote tuner, however a second wire sounds like would be a good idea.  The building height will be about 16 feet.  Because of a small shed and bushes, a sloper is a no go.    I like John's idea, just try it.

30' above the tin roof might act as a pretty good counter-poise at 1/8th wave.

[N0WEK]

One other consideration is that all that metal is not well bonded together. Some of those less than perfect, and probably corroded, connections will act as diodes and cause all sorts of problems.

[KE7XD]

N0WEK – I was concerned about that also.  I checked and there are sheet metal screws every few inches.  These actually cut into the metal as they were installed, and most appear to be still tight.  Also there is a cap that wraps around from the roof to the sides, and also screwed every few inches.  Still a very legitimate potential problem.  Thanks !

[N0WEK]

N0WEK – I was concerned about that also.  I checked and there are sheet metal screws every few inches.  These actually cut into the metal as they were installed, and most appear to be still tight.  Also there is a cap that wraps around from the roof to the sides, and also screwed every few inches.  Still a very legitimate potential problem.  Thanks !

The screws should be much better than the old nails.

It's worth a try!