Doublet length and balanced-line length are selected together to transform impedances on several bands toward values that are easier to match.
Antennas · F1SYH
ZS6BKW antenna
The ZS6BKW is a multiband doublet with a balanced-line section optimized to present more favorable impedances on several amateur bands.
HF
Multibande
Optimisée
Operating principle
Main characteristics
Typical gain
Variable selon bande
Impedance
Variable, souvent plus favorable
Polarization
Horizontale
Difficulty
Intermédiaire
Dimensions and design
A common implementation uses about 28.5 metres of total wire and a balanced section whose physical length depends strongly on velocity factor.
Construction and tuning
Step 1
Determine the line velocity factor accurately.
Step 2
Calculate physical length from electrical length.
Step 3
Build the doublet symmetrically.
Step 4
Keep the balanced section vertical and clear.
Step 5
Check every band before final trimming.
Advantages
- Often a better multiband compromise than a standard G5RV.
- Efficient doublet radiator.
- No traps or loading coils.
- Accessible wire construction.
Limitations
- Dimensions depend on the actual line.
- Matching is still required on some bands.
- Balanced line is environment-sensitive.
- Requires considerable span.
History and origin
The design was developed and analyzed by Brian Austin, ZS6BKW, through optimization of the G5RV-type system.
Safety
Maintain clearance around the balanced line, especially at high transmitter power.