We have a gate opener with keyfob-type RF remote transmitters that operate at 318MHZ. The range from inside the car is about 75 feet -- less than we'd like due to the time taken by the gate operators to function.
The antenna is approximately 9" long, and mounted vertically on top of a metal fence post; the fence is about 1" metal mesh (similar to poultry netting) with a vinyl coating; I don't believe the fence is electrically connected to the post (at this time) due to the vinyl coating and paint on the post.
The antenna is connected via coax to the receiver; I believe the coax is grounded to the fence post via its mounting bracket.
From an online antenna length calculator, a quarter wave antenna for this frequency should be 8.83", so I believe the antenna itself is OK; my question is whether there is anything that can be improved about the way the antenna is mounted that would improve the range? The gate is at the mid-point of the driveway, so a unidirectional solution doesn't seem appropriate.
Edit: here's an rough diagram of the area; it's about 120' line of sight to the house and maybe 100' to the turn in the driveway toward the street. The area is wooded, and there are some low-hanging branches, but generally a clear line of sight from the house to the antenna.