Monday, February 20, 2006

A low-cost 2 elements for 40m





Objectives: - Improve reception toward NA, by attenuating EU-signals
- Provide some substantial gain over my usual dipole (3.5~4dB)
- easy to erect/remove




Playing with MMANA and NEC2 I discovered that placing a passive reflector some 8m (0.2 wl) behind my standard inverted V-dipole, I could get near to 4dB gain, while maintaining an acceptable SWR in the 50 ohms line (typ 1.7).
I also discovered that the passive reflector could be noticeably lower than the dipole, just sacrifying a few tenth's of DB.

Above: the concept, and the simulated performances (in red) compaired to a dipole at the same height (in blue) and to a 4 radials GP at 10m (black)

Below: the practical realisation with the dipole at 19m (7m above the tribander), and the passive reflector with the appex at 15m. The reflector can easily be folded along the fiberglass mast to restore the bidirectional pattern of the dipole... In the background, the 380kV power-line !

1 comment:

F4EGZ ced said...

Bonjour, effectivement l'ajout d'un reflécteur de ce type sur un dipole en V inversé fonctionne parfaitement. Weekend dernier nous avons réalisé sur le meme principe une 5 éléments en V inversé à 12m du sol. Qui donne de trés bon résultat. Peut etre à ce weekend pour la coupe du ref.
73 cédric F4EGZ (TM5J team)