Friday, August 21, 2009
6m vertical rectangle
Also known as UB5UG's rectangle
and Skydoor by JA1HWO.
I chose UB5UG's variant because it's more convenient - no need for matching/balun unit and no need to split lower bar.
I tried to connect and disconnect cable's braid at the center of lower bar - it doesn't affect SWR. Therefore I'll leave it connected as UB5UG suggested for desymmetring purposes.
Computer modeling (mmana) clearly showed that:
1. horizontal bars must be significantly thicker than vertical ones, otherwise
performance is suffering noticeably. (first I thought to make them from plastic or bamboo but after computer modeling I abandoned this idea)
2. using isolator in vertical wire is not necessary.
Its gain is about 3dBd in free space. When mounted on 2.5 meters high (middle of my 5m fishing pole) it has 9dBi and 20 degree take-off angle.
Update - can't figure out why 4nec2 shows 7.78 dBi vs 9.4 dbi in mmana :(
at the same heights and same ground parameters...
Anyway, in reality antenna shows low SWR.
Must wait for propagation and test it in real QSO not in PC hihi
73 Zilvis, LY2SS