"Ed_G" wrote in message
. 192.196...
Owen Duffy wrote in
:

"Ed_G" wrote in
. 192.196:



No, I wouldn't say "shield" would be a proper
term, either.
But I
would suggest that a "cancellation" similar to
radiation in a
balanced feedline, would be pertinent.


Then I will leave you to your view that the system is
balanced.

Owen



I would have preferred an explanation of your view on
why it
wouldn't
be, but I thank you for all your prior discussion.

From my first post on the topic:

"If Ed connects parallel line from the centre of the
dipole to the hot
and
common terminals of the ATU, there is likely to be common
mode current
on the parallel line adjacent to the ATU. If the only
connection on
the tx side of the ATU is the coax, then it will also
have a common
mode current adjacent to the ATU and near enough to equal
to the
common mode current on the other side of the ATU."

Sure, you can fabricate a parallel line from two coaxial
lines, it
just has much more loss than a conventional air spaced
line... and
although it is short, you intend operating it at extreme
VSWR. The
shielded twin line you synthesise does not have any magic
properties
in supressing or shielding feed line radiation.

Note that I am avoiding the term balanced line that some
have used.
Balance is not forced by line geometry, but is a result
of the
environment, so balanced lines are balanced by external
factors, not
the line geometry.

Owen

PS: I wonder if you had considered end feeding the
Inverted V with the
ATU. IIRC you had a sheet metal roof. You could just fix
the tuner to
the roof, connect the ground terminal to the roof sheet,
and take a
wire from the ATU output terminal to the end of the
inverted V (which
is a continuous conductor across the apex). This is an
unbalanced load
connected to an unbalanced output. Is that too easy?




Owen, after reading Roy's explanation, I came back
to this one
and what you have been saying is now more clear to me.

I will have to check what is available for end feed on
the roof,
but it is a completely rubber covered roof and I doubt
there is any
convinent way to access a ground. Tnx.

Ed



-------------------


What about running radials made of lengths of burlar alarm
metal tape? A coat of black spray paint will make them
nearly invisible on a black roof.

I didn't see your frequency requirements, but I have had
excellent results from a Cushcraft R7. I am amazed at just
how well it works, even on 75m (by accident!).

Ed, NM2K