At resonance the traps present high impedance and isolate the outer sections. On lower bands they contribute to the total electrical length.
Antennas · F1SYH
W3DZZ antenna
The W3DZZ is a multiband dipole using two resonant trap circuits installed symmetrically in the legs.
HF
Multibande
Pièges LC
Operating principle
Main characteristics
Typical gain
Proche du dipôle sur chaque bande
Impedance
Proche de 50 à 75 Ω
Polarization
Horizontale
Difficulty
Avancée
Dimensions and design
The historical version mainly covers 80 and 40 metres. Trap frequency and inner and outer wire lengths must be tuned together.
Construction and tuning
Step 1
Build two strictly identical traps.
Step 2
Measure their resonance before installation.
Step 3
Cut the inner sections slightly long.
Step 4
Add the outer sections.
Step 5
Install a 1:1 current balun.
Step 6
Tune the higher band before the lower band.
Advantages
- Two main bands without a tuner.
- Simple coaxial feed.
- Dipole-like pattern.
- Additional traps may be added.
Limitations
- Trap losses.
- Bands interact during tuning.
- High capacitor voltage.
- Mechanical weight in the legs.
History and origin
Chester L. Buchanan, W3DZZ, popularized the design during the 1950s as a coax-fed multiband antenna.
Safety
Trap capacitors must withstand RF voltage and be weatherproof.