Galvanized iron - a poor ground plane?
 

I have been considering a vertical setup on the top of my galvanized
sheet metal roof and using the roof as a ground plane. My brief tests
so far indicate that the performance of such a setup does not deliver
as strong signals to my RX as my simple inverted-V. Nevertheless, my
roof is only 2 years old, still in good condition and with well
overlapping sheets.

There may be various reasons for this, but it has occurred to me that
the galvanized roof may not be such a good RF-conductor. Due to the
skin effect much of the current would run in the zinc coating, for
which I do not have much information on as far as RF-conductivity goes.
Does anyone have a comment or suggestions on this?

By the way, I am going to try to lay additional wire radials (aluminum
welding wire) on this roof, which is the subject of a post I just sent
out before this one.

73 - Kristinn, TF3KX

Galvanized iron - a poor ground plane?
 

The RF resistance of the galvanized steel roof will be sensibly zero
due to the very large area of the 'skin'. (relative to diameter of
radial wires).

If you wish to use radials they may just as well be attached to the
edges of the roof. This will effectively increase the area of a small
roof.

The difference in received signal strength compared with an inverted-V
is probably due to the difference in polarisation. A vertical on the
roof may be better for DX.
----
Reg, G4FGQ

Galvanized iron - a poor ground plane?
 

TF3KX wrote:
I have been considering a vertical setup on the top of my galvanized
sheet metal roof and using the roof as a ground plane. My brief tests
so far indicate that the performance of such a setup does not deliver
as strong signals to my RX as my simple inverted-V. Nevertheless, my
roof is only 2 years old, still in good condition and with well
overlapping sheets.

There may be various reasons for this, but it has occurred to me that
the galvanized roof may not be such a good RF-conductor. Due to the
skin effect much of the current would run in the zinc coating, for
which I do not have much information on as far as RF-conductivity goes.
Does anyone have a comment or suggestions on this?

The surface area is so large that you wouldn't be able to tell the
difference between zinc and a perfect conductor.

By the way, I am going to try to lay additional wire radials (aluminum
welding wire) on this roof, which is the subject of a post I just sent
out before this one.

That doesn't make any sense to me, unless you're concerned about the
quality of the contact between sheets. Even then, I'd think that the
capacitance would be adequate.

Roy Lewallen, W7EL

Galvanized iron - a poor ground plane?
 

TF3KX wrote:
I have been considering a vertical setup on the top of my galvanized
sheet metal roof and using the roof as a ground plane. My brief tests
so far indicate that the performance of such a setup does not deliver
as strong signals to my RX as my simple inverted-V. Nevertheless, my
roof is only 2 years old, still in good condition and with well
overlapping sheets.

There may be various reasons for this, but it has occurred to me that
the galvanized roof may not be such a good RF-conductor. Due to the
skin effect much of the current would run in the zinc coating, for
which I do not have much information on as far as RF-conductivity goes.
Does anyone have a comment or suggestions on this?

By the way, I am going to try to lay additional wire radials (aluminum
welding wire) on this roof, which is the subject of a post I just sent
out before this one.

73 - Kristinn, TF3KX

Hi Kristinn,

Effectively the radials will not even be seen by the Antenna because of
the large metal surface area of the Roof. As Reg Suggests the only way
you may improve the situation is to attach radials to the roof edge and
have them extend the length of the ground plain system. A better method
under the condition you have stated may be to be sure the bond between
roof panels is RF/electrically good and add radials to by connecting
them to the roof panels at the edge of the roof. You do not mention the
Frequencies of Interest. Aluminum on Zinc is not a good Idea. There
will be interaction and it will create noise on RX in short order.

you would be better off raising the radials off the roof by some
distance if you decide to go that root.

hope this helps. 73 Dave, KC1DI