with a 450 Ohm type. The final ZS6BKW antenna is a 2 × 13.75 m dipole fed with a 12.2 m long 450 Ohm ribbon line. The feeding point here is also 50 Ohm.
better SWR is very dependent on antenna height, subsurface, environment and applied "hardware". Other versions of a ZS6BKW probably were figured out because the designers or publicists aimed for an lower SWR at their location.
COAX FEEDER
The feed point of a ZS6BKW is 50 Ohm, but count of 'about' 50 Ohm, because a random length of coaxial cable works as an impedance transformer. As a result, it is possible that the transmitter is loaded with an impedance lower or higher than 50 Ohm, confirmed by the SWR meter. Suppliers of ZS6BKW or G5RV advise or mention explicitly that their product only works well with a certain length of coaxial cable.
Use preferably a ½ wave (½λ) coaxial cable at the lowest frequency. That works for many bands as 1 ÷ 1 transformer, so that the transmitter at the beginning of the cable has the same impedance of the antenna system.
I prefer to use a multiple of 6.70 m, 50 Ohm/V 0.66 coaxial cable. For 10 - 40 m it is 2 × 6.70 m = 13.4 m and for 10 - 80 m it is 4 × 6.70 m = 26.80 m.
It is also better to install a balun (choke balun) between the asymmetrical coaxial cable and the symmetrical 450 Ohm ladder line. For example by winding close to the feedpoint an about 6 m coaxial cable on a pipe of 7 - 12 cm in diameter. An other line insulator can be made by applying as many windings as possible of RG58 types coax on a FT240-43 toroid.
ZS6BKW Other versions Antennas, Antennas for Ham Radio.
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