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.

Siehe dazu auch "Rothammel 12. Auflage, Kap.8, Seite 166!

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