I found the helix not to be such a good antenna for point to point in this case. The final design was a 10 element Quagi( quad driven element and reflector with yagi directors). The Quagi has the advantage of being polarity selective. The antennas were mounted for horizontal polarity thus rejecting much of the mostly vertically polarized interference.
I also discovered that on the WRT54s that the antenna ports can be operated with one port as transmit and the other receive at least if you are running DD WRT software .
Jimmie