[Elecraft] Open Line Feeder

[W3FPR - Don Wilhelm]

Lee,

The impedance at the end of an open wire transmission line depends on the
line length and the antenna, If you know the antenna feedpoint impedance and
the transmission line length, a program like TLW (from ARRL) can predict the
impedance that must be matched at the tuner.

In many cases, a 1:1 balun (or no balun at all) will serve better than a 4:1
balun.  The impedance that has to be matched by the tuner will almost always
be something quite different than the characteristic impedance of the
transmission line.  Feedpoint values ranging from only a few ohms to a few
thousand are not unusual for a multiband antenna.

Yes, you can use your 4:1 balun, but if you have trouble matching the
antenna system on some bands, just take the balun out and feed the
transmission line directly, one wire to the coax connector center and the
other wire to the ground terminal.  The transmission line will still be
balanced as long as the antenna is being fed at its electrical center - the
fact that the current at the ends of the antenna must be zero will assure
that the feedline will be balanced.  You may check out LB Cebik's info on
multiband antennas too if you have doubts, he states it in a different
manner than I do, but the end result is the same - you don't really need a
balun in all cases and connecting directly to an unbalanced tuner will do no
harm especially in a portable situation.

73,
Don W3FPR

> -----Original Message-----
>
>
> Field Day is coming up and the K2 is going out.  I
> have the KAT100 as well...and I want to put up a 130
> foot dipole with that ladder line stuff.  Hey, its
> only for 24 hours.  To use the KAT100, I have a 4:1
> balun (a 4KW job).  Can I use that with the KAT100 and
> the open line feeder?  What are all you guys doing?
>
> Lee - K0WA
>
>
> Common sense is in short supply - get some and use it  - Lee Buller
>