How Should I Implement My New True Ladder Line Antenna System?
Our Antenna/TrueLadderLine systems are designed to operate with very high efficiency (90% or better) on all the bands from 160 meters through 10 meters using no loading coils and/or tuned networks in the antenna.
Our TrueLadderLine 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 feed 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).
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!
We are very concerned about acquiring high efficiency (90% or better) on all the bands we wish to operate, 160M through 10M. The issue with our antenna systems is whether the ATU can resolve the impedance presented to it by the antenna feedline.
We offer free system modeling to determine the impedance presented to the ATU, system efficiency and feasibility for the bands of operation desired. If you wish to have your system modeled before you install it, feel free to call Gary K7EMF at 509-290-0414 to discuss your application.
If you wish to perform the modeling yourself, we offer free software which is extremely accurate. SimNec is available in our store and located in our product categories as "Antenna System Modeling Software". When you click on that product, you will be provided with a link to download SimNec, no charge. If you place an order for the software, there is no cost and we will receive your email address so we can email you circuit files to immediately get SimNec operating for various antennas and feed system configurations. We at TLL use SimNec for our modeling and have had great results!
All feedline when operated in a high SWR situation acts as a transformer which transforms the antenna feedpoint impedance to a different impedance. TrueLadderLine is no exception. High SWR on the feedline will cause excessive loss unless the matched loss of the feedline is extremely low. TrueLadderLine fits this category due to it's extremely low loss!
Because the ladder line transforms the antenna feed point impedance presented to the ATU (due to high swr on the line), the length variation will change the impedance presented to the ATU (see "Feedline Length Modeling" tab at top of store page).
Impedance transformation to the ATU can be readily modified by changing the ladder line length. I have found that this method works very well for 80 meters up to 10 meters. 160 meters requires larger changes in ladder line length to afford the impedance change necessary. Therefore, I prefer to keep my ladder line fairly short (45 to 55 feet) to present a reasonable impedance to the ATU for 160 meters. The other bands fall into line reasonably well. I also have discovered through many system models that the impedances presented to the ATU for 160M and 80M are much easier to resolve by the ATU if I can keep the antenna feedpoint at least 45 feet above ground.
I have optimized my antenna system for 160-80-40 meters which results in a system efficiency in the mid 90% range! This system is comprised of a center fed dipole (feedpoint 55 feet above ground) 215 feet long and a TrueLadderLine length of 45 feet. The Balanced ATU is located at the base of the tower and remotely controlled with a StepperTune-BT. The antenna length of 215 feet results in a reasonably low SWR (on the ladder line) on all three bands simultaneously which affords efficiency numbers in the high 90% range!
I also prefer an Inverted V configuration which has a near Omdi-Directional pattern! If your real estate can not accommodate a full 215 feet, folding the ends down toward the ground along a non-metallic support works well also. With the ends folded downward, I try to keep them at least 10 feet above ground.
I look forward to having a QSO with you on the air! Best 73's, Gary K7EMF