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frequently asked questions

Such values have been very often discussed, but are of minor importance! They are important in case of a ladderline used as a TRAVELLING WAVES FEEDER! But as a STANDING WAVES FEEDER for a symmetrical antenna - dipoles! - the antenna works as a MULTIBAND-SYSTEM! CONSEQUENTLY for reaching this you must combine it with a BALANCE ANTENNA TUNER for all bands; thus producing the typical antiphased RF along the ladderline.

This is important for such ladderlines which shall be used as a TRAVELLING WAVES FEEDER. The distance between the two wires are responsible for the line-impedance. Such application is to find in MONOBAND-SYSTEMS.

For STANDING WAVES FEEDERS, the typical impedance figures have no importance. The other reasons for different spreaders are as follows:

  1. In salty atmospheres near the coastlines, the longer spreader is the better solution for minimizing RF-loss due to salt-water depositing to the spreader surface.

  2. QRO-Friends may use the longer ones. In case of a kilowatts power, the RF-Voltage becomes very high and this requires a good distance between the line-wires.

  3. The typical LINE RADIATION AND RECEPTION depends from the line wire distance. If the main activities are concentrated from 6 to 15m, the SP-50 is the right choice, for all the other bands, SP-120, SP-150 and SP-200 are ok!

  4. For friends of a 4-wire-feeder-system, the models SP-150 and SP-200 are prepared for it.


In our ham-language, it is another word for 2-wire-feeder. Originally, this system has been invented long time ago by Professor Lecher from Austria, and for this reason it is called sometimes the Lecherline too. our french friends are calling it "echeles a grenouilles", which means "frog-ladder" and we in DL are saying "Hühnerleiter", which is the same as "chicken-ladder". But the word "ladder-line" is describing it correctly in the same way!

The most advantageous mode of operation is the STANDING-WAVE-FEEDER, together with a balanced or symmetrical antenna-tuner. It means in this case, that the use of standing waves is the best way for a highly efficient feeding system. This is completely different to the coax-feeder, which works better without standing-waves.

WHY? The coax-cable insulation - mostly polyethylene - is stressed by the RF-field between the center conductor and the shield and converts a small energy amount to warmth. This depends directly of the frequency in use: the higher the frequency, the higher the loss! In addition to this, this loss is increased considerably by a bad SWR-figure. There are enough statistics for this effect in the amateur-radio litterature! Unfavourable SWR-values are occuring normally with coax-feed resonant antennas and the impression that a correction of such bad values by a tuner is an error: the good values are referring only with respect to the tranceiver output, but are not at all improving the bad SWR along the coax!

The ladderline is 99%-air-insulated and has practically NO-LOSS! And by the reason, the STANDING-WAVE-APPLICATION is absolutely without negative influence to the efficiency of the feeder, just in contrary to a coax-cable.

Yes, the coax are ok, but you can do things a lot better with ladderline-feeding of antennas!

For example:

  • Reduction of TVI and BCI.
  • A dipole-antenna operates on all bands with a SWR of 1,0. BUT: the use of a balanced tuner is absolutely necessary to reach this standard.
  • Following the lay-out of your antenna, the ladderline-feeder can ba a lightweight-solution compared to a coaxcable!

There is a number of systems in use, which represents different qualities.

Two of these are:

The NON-SYMMETRIC-TUNER with additional 1:4-Balun

This is a not recommendable system for ladderline-feed antennas. The match and efficiency are interdependent a good function requires a line impedance of near to 200 ohms and this can be reached only for a very limited frequency range. A mismatch is easily possible and results in lossy operation or a correct match remains possible for only some frequencies! Further the danger for TVI & BCI is considerably high!

The BALANCED or SYMMETRICAL TUNER

The balanced or symmetrical tuner is designed normally with an balun 1:1 at the input and a number of variable capacities and indutivities, thus generating the counterphased RF at the tuner output.

 

For instance :

  1. Double-Circuit with Input-Balun: simple and low-cost
  2. Hipass-T-Circuit with Input-Balun: very extended impedance matching range
  3. Double-Collins-Filter with Inpu-Balun: extended impance matching range

 

Summary:

Only the balanced- or symmetrical-tuner is able to generate the counterphased RF for ladderline-feeders on all bands, with a minimum of feeder-fadiation.

Also look at "Rothammel 12. Edition, chapter 8, page 166!

Not more difficult as with a coax-cable! Even a window-frame means not a problem!

1) For powers up to 250 watts::

  • 2 exactly equal lengths of RG-58U. The length depends of the distance from the ladderline-end to the tuner-input connections - measure it as short as possible!
  • Place these 2 lengths exactly in parallel.
  • Prepare 2 holes of 7mms dia through the window-frame, push the two cables through until the end of the ladderline. Connec only the 2 centerconductors to the ladderline, protect these 2 connections against moisture!!!
  • Now hold the 2 cables parallel by applying some pieces of adhesive tape!
  • The tuner-end of the cables are prepared by soldering the 2 shields together plus a grounding-wire, which has to be connected to the grounding post of the tuner! The 2 center-conductors to be linked to the output posts of the tuner.

 

2) For powers higher than 250 watts:

The same as before, but now with stronger coax like RG-213U or better a teflon-insulated coax, which is thinner!

To go through a wall means not big holes, but 1 hole of 20mms dia is sufficient for the 2 coax in parallel, even a third coax for your beam can be placed adjacnt to the 2 ladderline-feed-cables without negative influences

A normal stranded Cu-wire of 1,5 mm2 is ok for 1 kW of power! May it be insulated or not. A special antenna-wire is not necessary!

No! There is only a tiny increase of the shortening factor, the operation capacities are the same as with non insulated wires.
No but it is a question of personal requirements! If the lower prices and high mechanical strength are of major importance, then you may have good results with such wires too. There will be a slightly lower efficiency caused by the higher resistances in ohms. But this is practically out of consideration. The SW Broadcast-stations are using stranded bronze wires and are doing a good job: this wire has a resistance higher than the same in copper. Aluminium-wires are low-priced by mass production for electric fences. Ok for antennas, but stiff and breaks easily. Advantage: Lightweight! there are copper plated steel-wires on the market: very good and better than normal steel wires!

Yes, the system ladderline to antenna, correctly matched with a balanced tuner has practically no radiation from the feeder, due to the self-neutralizing on the parallel-wires by the counterphased RF-currents. Another reason is the strictly symmetrical layout: there is no need of a support from the ground, such antenna is self-supporting! Arisk of coax-feed antennas is a possibility of radiations from the coax, if there are bad swr-values in operation, due to non resonant antennas. These RF-voltages from the coax are floating "in-house", there causing TVI and/or BCI!

This antenna-design is broadbanded and will be shorter for a certain frequency than a single wire dipole. The matching-requirements are easier, because of the larger width of the SWR 1:2 range. This antenna can be a good solution for limited space in the garden!
   
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