Hal Rosser wrote:

"Dan Richardson arrl net" k6mheatdot wrote in message
.. .
In your original post you said:

"The only thing I have against them (current baluns) is
They are heavy.
and cause the antenna to droop lowering the height of the feedpoint."

Anyway, with say fifty pounds of tension just how much drop are you
talking about? And what difference does it make?


Apparently it makes more difference to me than it does to you.
I don't want it digging into the tree branches.

That's a fair point. The sag in a dipole supported only at the ends is
very sensitive to the suspended weight in the middle. And if the end
supports are trees, the problem can become extreme.

Nothing wrong with your view - its probably a better-informed view than
mine - but I'll still use balanced line and I still think baluns are too
heavy. I'm just hard-headed that way. :-)

If sag is a problem, don't use 300 or 450-ohm ladder line. In terms of
weight and windage, it is a very bad solution. A much more practical
solution is to make your own ultra-lightweight parallel line. The wire
can be much thinner than the main antenna, and you can use a spacing of
several inches with the absolute minimum number of ultra-lightweight
spreaders.


But more important than that, please stop calling it "balanced line".
Somehow we have got into the habit of kidding ourselves that
parallel-wire line is balanced line. It isn't!

Parallel line does NOT automatically balance itself. It will cheerfully
allow unequal currents on the two wires. That's the same as saying it
will cheerfully support an unwanted common-mode current (same magnitude
and same direction on both wires) in addition to the wanted
equal-and-opposite currents.

So parallel line will NOT be balanced line - not until you have done
something to MAKE it balanced.

The one best way to create a balanced feedline is to make the layout of
the antenna and feedline is completely symmetrical with respect to
ground - and that includes the entire run of feedline back to the shack.
Unless you have taken the trouble to do that, you WILL have common-mode
currents on the line and it WON'T be balanced. The common-mode current
may not be large enough to cause a practical problem... but don't ever
kid yourself that it isn't there.

Because it's difficult to use a choke balun with parallel-wire line, and
because of the weight problem, about the only practical place where you
can stop common-mode currents is at ground level. A choke or a
link-coupled ATU will force a minimum in the common-mode current at that
position; but a quarter-wavelength up the line towards the antenna, it
will also force a maximum in the common-mode current (and if the line is
long enough, these maxima will repeat every half-wavelength). With
parallel-wire feedline, your only defence against that problem is a
symmetrical layout.



--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek