If a helix is built correctly you can get some great range out of them but you need them both to be matched, If you have wired them left hand they both have to be that way otherwise you will get naff all signal. Also the feeder and wire has to be prety close to perfectly spaced otherwise this will degrade your signal.

For this link I think you would be better off with another type of antenna. Not trying to pimp our products but http://shop.borg.co.nz have a reasonably inexpensive 14dbi pannel antenna that would work well for your installation.

Als it would be a good idea to check your cables, make sure they have been correctly made as if a pin is out of place or there is a short you would get the same thing.

Regards
Andrew Hooper