Balanced line carries high impedances with lower loss than coax. Antenna, line and tuner must be considered as one system.
Antennas · F1SYH
Multiband doublet
A multiband doublet is a dipole that is not necessarily resonant, fed with low-loss balanced line and an antenna tuner.
HF
Multibande
Ligne bifilaire
Operating principle
Main characteristics
Typical gain
Variable selon bande
Impedance
Très variable
Polarization
Principalement horizontale
Difficulty
Intermédiaire
Dimensions and design
Length is not critical, but some values create impedances that are difficult to match. Unfavourable line resonances should be avoided.
Construction and tuning
Step 1
Use the greatest practical span.
Step 2
Build symmetrical legs.
Step 3
Use good balanced line.
Step 4
Keep the line away from metal.
Step 5
Use a truly balanced tuner.
Advantages
- High efficiency.
- Wide HF coverage.
- No traps or loading coils.
- Low feed-line loss.
Limitations
- Requires a tuner.
- Balanced line installation is restrictive.
- Some extreme impedances.
- Large physical span.
History and origin
The open-wire-fed doublet is one of the oldest and most efficient multiband antenna systems.
Safety
Balanced line may carry high RF voltage and must remain inaccessible.