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True Ladder Line and Wire Antennas

How Should I Implement My New True Ladder Line Antenna System?

Posted by Gary Baker-K7EMF on

How Should I Implement My New True Ladder Line Antenna System?

600 ohm ladder line is extremely low loss feed line which lends itself well to operating under high swr conditions.  By using a single wire dipole antenna for multiple bands, the swr on the feedline will be high.  With extremely low loss feed line such as True Ladder Line, these swr losses are negligible.  The net result is a highly efficient antenna system.

We need to think of our antenna as a system, not just an antenna.  So the question is:  how do I get as much RF power to the antenna as possible through my antenna system?  The answer is low loss feedline combined with a tuner that can resolve the impedances presented to it by the feed line over a wide range of frequencies (bands).

Here are the choices we have (most efficient to least efficient):

A)  Ladder Line from antenna feedpoint to the Balanced ATU at the transmitter location (in the shack).  

B)  Ladder Line from antenna feedpoint to the Balanced ATU at the base of the antenna support structure and fed with low loss coax into the shack.  This affords a 1:1 match for the coax and minimal loss!  The remotely located ATU may be remotely controlled via stepper motors and a steppertune controller (see at www.steppertune.com).

C)  Ladder Line from antenna feedpoint to the Unbalanced ATU (with 4:1 balun at output of ATU) at the transmitter location (in the shack).

D)  Ladder Line from antenna feedpoint to a 4:1 balun located outside the shack and fed with coax (short as possible and low loss) in to the unbalanced ATU in the shack.

Because the feed line transforms the feedpoint impedance, the length variation will change the impedance presented to the ATU.  Therefore, it is a good idea to use the "taboo length" table if one is using a typical commercially available ATU.  If one is building his/her own ATU, then it is possible to design an ATU that can resolve the wide range of impedances presented by the feed line.

Keep in mind that system efficiency is a function of keeping a low swr (1:1 match) on any coax used in the system.  If that is not possible, then keep the coax run (with high swr) as short as possible and use extremely low loss ladder line as much as possible.  This will make the system losses as low as possible and thus a bigger signal!  

I look forward to having a QSO with you on the air!  Best 73's, Gary K7EMF