On Jun 1, 2:43 pm, wrote:
What is the result of using a metal mast as the center support of an inverted V
antenna. Will it work and if so can resonable low SWR be obtained using a
tuner? Any advice appreciated.

TIR

I actually prefer a metal mast. In case of a lightning strike, the
mast
takes the bulk of the energy to ground, instead of my coax doing all
the
dirty work. A vertical on top of the mast can act as a lightning rod,
so all bets are off on those. But with my coax supported a foot or so
below the tip of the mast, feeding dipoles, I've taken strikes with no
coax
damage so far. There is some energy that runs the feedlines, but it's
fairly
small compared to the mast itself. It's enough to make an audible arc
sound
at my coax/bulkhead ground connection though. Thats with the
connectors
screwed in too.. I've never noticed any real RF coupling problems with
a
metal mast. You will see that with metal that parallels the antenna
legs
themselves. One of the worst coupling problems I ever saw as far as
tuning, was with a set of dipoles used next to a large mobile home.
All that metal surface gave us a fit. I had to try quite a few leg
locations/wire
lengths before I could get it tuned halfway decent. That was one of
the
rare cases I've seen where even the lowest band had problems.
MK

wrote:

...
screwed in too.. I've never noticed any real RF coupling problems with
a
metal mast. You will see that with metal that parallels the antenna
legs
...

Amazing we have not heard from the "EZNEC Experts" with plots of a metal
vs. non-metal support ...

JS

On Jun 3, 9:45 pm, John Smith I wrote:
wrote:

... screwed in too.. I've never noticed any real RF coupling problems with
a
metal mast. You will see that with metal that parallels the antenna
legs

...

Amazing we have not heard from the "EZNEC Experts" with plots of a metal
vs. non-metal support ...

JS


If the wires of the dipole are exactly perpendicular to the feedline,
and
no common mode currents, the plots should be the same.
The more sloping, the more coupling I would think, but even then,
it's rarely a problem.
MK

wrote in
oups.com:

On Jun 3, 9:45 pm, John Smith I wrote:
wrote:

... screwed in too.. I've never noticed any real RF coupling
problems with
a
metal mast. You will see that with metal that parallels the antenna
legs

...

Amazing we have not heard from the "EZNEC Experts" with plots of a
metal vs. non-metal support ...

JS


If the wires of the dipole are exactly perpendicular to the feedline,
and
no common mode currents, the plots should be the same.
The more sloping, the more coupling I would think, but even then,
it's rarely a problem.

Modelling the Inverted V without its support conductive mast is a little
like modelling it without a real model of its feedline, both ignore real
things that impact the antenna to some extent.

Owen

Owen Duffy wrote:
wrote in
oups.com:

On Jun 3, 9:45 pm, John Smith I wrote:
wrote:

... screwed in too.. I've never noticed any real RF coupling
problems with
a
metal mast. You will see that with metal that parallels the antenna
legs
...

Amazing we have not heard from the "EZNEC Experts" with plots of a
metal vs. non-metal support ...

JS

"John Smith" doesn't hear from this "EZNEC Expert" because I plonked him
a long time ago.

If the wires of the dipole are exactly perpendicular to the feedline,
and
no common mode currents, the plots should be the same.
The more sloping, the more coupling I would think, but even then,
it's rarely a problem.

Modelling the Inverted V without its support conductive mast is a little
like modelling it without a real model of its feedline, both ignore real
things that impact the antenna to some extent.

Owen

If you model the antenna as being perfectly symmetrical, then it makes
no difference whether you include the mast in the model or not -- the
result will be the same (assuming that the mast isn't in electrical
contact with the antenna). It might be interesting to purposefully make
the antenna model a bit non-symmetrical to see what effect the mast
would then have.

If you're not using an effective balun, adding a feedline to the model
will have an impact on the result (as it will on a real antenna) even if
the antenna is symmetrical, provided that you include the common mode
current path in the feedline model. This means modeling the feedline as
two wires, or by using the transmission line object plus a wire to
represent the outside of a coaxial cable. To be truly realistic, you
need to include the entire path to the Earth. This is seldom known, so
about the best you can do is to fiddle the length and orientation of
your feedline model to find the worst case and assume the real antenna
will have less common mode current than that.

Roy Lewallen, W7EL

Roy Lewallen wrote:

...
"John Smith" doesn't hear from this "EZNEC Expert" because I plonked him
a long time ago.
...
Roy Lewallen, W7EL

Roy:

You dropped out of being on the cutting edge long before I ever came along.

Don't even attempt to blame me for you devote religious beliefs in
established practices which are cloaked in "place-holder equations" ...
you only become ancient and unimportant when you quit adapting to change.

JS