"Owen Duffy" wrote in message
...
" wrote in news:6d1a078a-e5f4-
:

...
Though the traditional approach has been to use a 4:1 voltage balun at
the rig to feed these things, there is good argument to use a 1:1
Guanella balun (current balun), and it can be located outside the shack
and inboard shield effectively grounded to deal with common mode current.
You still need to minimise the length of coax operated at high VSWR, and
it would not be necessarily absurd to think about low loss coax.

Owen

Okay, then it might make sense to do this: Plan II

instead of using the balun is in the tuner, there is no reason
why I couldn't mount another 4:1 balun outdoors, and use a short run
of low loss coax back through the conduit into the operating room.

That would be about 15 feet of LMR-400 cable. I could go to 1/2 heliax
but would there be any benefit??

So, I would have balanced open-wire feedline from the dipole to
the 4:1 balun followed by a 1:1 common-mode RF choke with
the requiste RF ground for decoupling,
followed by the short run of low loss coax going back to a
unbalanced ant. port on the tuner. I'd still have coax in the mix,
but the 4:1 balun should hopefully tame the high impedance
excursions across the antenna operating range to
reduce the coax's losses at those points?

Otherwise it is going to be hard to get balanced line into the shack,
unless I pull it through the PVC conduit with the other coax cables.

Pete

"Pete Bertini" wrote in newsiwTn.64499
:

So, I would have balanced open-wire feedline from the dipole to
the 4:1 balun followed by a 1:1 common-mode RF choke with


See my article entitled "Is a 4:1 balun a good choice for use with an ATU
on HF?" at http://vk1od.net/blog/?p=987 .

It is difficult to answer the question about the LDF without knowing the
impedances involved. I used TLLC ( http://www.vk1od.net/calc/tl/tllc.php )
to work the examples I gave, you could do the same if you know the
feedpoint impedance etc.

If you want to solve the cases for an arbitrary two wire line, try
http://www.vk1od.net/calc/tl/twllc.htm .

Owen

"Pete Bertini" wrote in
news
....
So, I would have balanced open-wire feedline from the dipole to
the 4:1 balun followed by a 1:1 common-mode RF choke with

I should have mentioned that 4:1 baluns integrated into ATUs are most often
voltage baluns.

When operated near a voltage maximum with high standing waves, they can be
very lossy. Sometimes it is claimed that they 'tame' difficult antennas
better than current baluns, which is often due to their internal loss. The
problem as such is not the balun, it is the extreme load presented by a
very poor antenna, and the lossy balun is a poor (grossly inefficient)
circumvention.

So, when a 4:1 voltage balun allows a match where a 1:1 current balun
doesn't, the problem is probably the antenna, not the balun.

Owen

That's pretty much what I've been reading on various websites.
At least some of the mystery is being cleared up A fan dipole
is starting to look better; at least I can control the feedpoint
impedance to within reason and keep a decent pattern on
the bands.

Pete

"Owen Duffy" wrote in message
...
"Pete Bertini" wrote in
news
...
So, I would have balanced open-wire feedline from the dipole to
the 4:1 balun followed by a 1:1 common-mode RF choke with

I should have mentioned that 4:1 baluns integrated into ATUs are most
often
voltage baluns.

When operated near a voltage maximum with high standing waves, they can be
very lossy. Sometimes it is claimed that they 'tame' difficult antennas
better than current baluns, which is often due to their internal loss. The
problem as such is not the balun, it is the extreme load presented by a
very poor antenna, and the lossy balun is a poor (grossly inefficient)
circumvention.

So, when a 4:1 voltage balun allows a match where a 1:1 current balun
doesn't, the problem is probably the antenna, not the balun.

Owen