I have erected various vertical and wire antennas from my roof, using
its metallic surface as a counterpoise (approx. 10x10m or 30x30ft). I
have come to suspect that there are some resistive losses in the roof
or the connections to it. My question is: Does anyone have a
suggestion for how to estimate by measurements the resistive losses of
the roof or its connection?

One idea might be erecting a quarter wave vertical for, say, 20m, and
measure the feed resistance. If modeling would suggest, say, an
"ideal" resistance of 35 Ohms, but the measured feed resistance would
be 45 Ohms, I could conclude that the extra 10 ohms were coming from
the resistance at the base, i.e. from the roof or its connections.
This assumes that the vertical had otherwise negligible loss (for
example, an aluminum tube). Now, to complicate things the roof is
sloping (approx. 45 degrees) and the antenna base is located at its
peak. This would be hard to model precisely, so that "ideal
resistance" would be hard to ascertain, to begin with.

Any other suggestions for estimating the roof connection losses?

73 - Kristinn, TF3KX

TF3KX wrote:
I have erected various vertical and wire antennas from my roof, using
its metallic surface as a counterpoise (approx. 10x10m or 30x30ft). I
have come to suspect that there are some resistive losses in the roof
or the connections to it. My question is: Does anyone have a
suggestion for how to estimate by measurements the resistive losses of
the roof or its connection?

One idea might be erecting a quarter wave vertical for, say, 20m, and
measure the feed resistance. If modeling would suggest, say, an
"ideal" resistance of 35 Ohms, but the measured feed resistance would
be 45 Ohms, I could conclude that the extra 10 ohms were coming from
the resistance at the base, i.e. from the roof or its connections.
This assumes that the vertical had otherwise negligible loss (for
example, an aluminum tube). Now, to complicate things the roof is
sloping (approx. 45 degrees) and the antenna base is located at its
peak. This would be hard to model precisely, so that "ideal
resistance" would be hard to ascertain, to begin with.

Any other suggestions for estimating the roof connection losses?

73 - Kristinn, TF3KX

I don't know of a good way to do it except modeling. Don't expect 35
ohms, though -- the resistance will depend on the size and shape of the
roof as well as height and diameter of the vertical, and can vary quite
a lot.

Roy Lewallen, W7EL

In article
,
TF3KX wrote:

I have erected various vertical and wire antennas from my roof, using
its metallic surface as a counterpoise (approx. 10x10m or 30x30ft). I
have come to suspect that there are some resistive losses in the roof
or the connections to it. My question is: Does anyone have a
suggestion for how to estimate by measurements the resistive losses of
the roof or its connection?

One idea might be erecting a quarter wave vertical for, say, 20m, and
measure the feed resistance. If modeling would suggest, say, an
"ideal" resistance of 35 Ohms, but the measured feed resistance would
be 45 Ohms, I could conclude that the extra 10 ohms were coming from
the resistance at the base, i.e. from the roof or its connections.
This assumes that the vertical had otherwise negligible loss (for
example, an aluminum tube). Now, to complicate things the roof is
sloping (approx. 45 degrees) and the antenna base is located at its
peak. This would be hard to model precisely, so that "ideal
resistance" would be hard to ascertain, to begin with.

Any other suggestions for estimating the roof connection losses?

73 - Kristinn, TF3KX

The REAL Question here is how are the Roofing Material Sheets bonded
together, both physically and electrically?

I have a Galvanized Steel Roof on my Cabin, where each sheet is spot
welded to it's neighbor in four places along the common length. This
provides a very effective RF Ground for a 4BTV mounted in the center on
the peak. clear down to 2006 Khz, with an applicable Tuner. I also have
a 130 Ft End-feed Longwire that uses the same Roof, via a SEA330
Autotuner for 2.0-22 Mhz Marine Operations. I have install a lot of
these type systems around Alaska for Fixed Comm's Systems over the last
3 Decades, and most are still in use even today. The bonding and
connections between the panels is the critical point for this type of
system, and Self-Tapping Sheet-metal Screws, just don't cut it in the RF
World. It isn't hard to do when installing the Roofing material in the
first place, but it IS hard to retrofit once the roofing is in place.

--
Bruce in alaska
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