When using the P10T and a UHF-R4 to do a point to point transmission with helical antennas, does the polarization direction of the helicals have to match or be opposite?
Matched - having the same polarization.
Here is an analogy: take two identical bolts. Thread a nut on to bolt #1. Now place the open ends of bolts together; the nut can be threaded off frrom bolt #1 on to bolt #2. The nut is the polarized RF wave. The bolts are the two antennas. The bolts share the same thread orientation or "polarization."
How to determine if a helical antenna is "left hand polarization" or "right hand polarization."
1) Position the antenna so it is parallel to the floor.
2) Place the base of the antenna to your left.
3) If the helical antenna element slants away from the antenna base, it is left hand polarization.
4) If the helical antenna element slants towards the antenna base, it is right hand polarization.