The balanced section is not simply a feed-line extension. Its electrical length transforms the doublet impedance differently on each band.
Antennas · F1SYH
G5RV antenna
The G5RV is a multiband antenna consisting of a doublet and a balanced-line section used as an impedance transformer.
HF
Multibande
Ligne bifilaire
Operating principle
Main characteristics
Typical gain
Variable selon bande
Impedance
Variable
Polarization
Principalement horizontale
Difficulty
Intermédiaire
Dimensions and design
The full-size version uses a doublet about 31 metres long and a balanced section about 10.3 metres long, corrected for line velocity factor.
Construction and tuning
Step 1
Cut both doublet legs symmetrically.
Step 2
Use balanced line with a known velocity factor.
Step 3
Keep the matching section away from metal.
Step 4
Install a choke at the coax transition.
Step 5
Use a tuner suitable for the impedance range.
Advantages
- Several HF bands.
- Relatively simple construction.
- Efficient doublet when high enough.
- Many documented variants.
Limitations
- Not truly all-band without matching.
- High SWR may occur on coax.
- Long coax may introduce losses.
- Balanced line must remain clear of metal.
History and origin
Louis Varney, G5RV, introduced the antenna in 1946. Its design placed particular emphasis on operation on 20 metres.
Safety
High RF voltage may occur on the balanced line.