If your gate motor is located behind a metal fence or other types of walls with metal framing, it can reduce the range of your remote control considerably because the radio waves from your remote control won't go through metal easily. Adding an antenna that is above the metal can solve this problem. However, just adding a wire as an antenna won't work because it upsets the tuning. Instead, the wire between the receiver and the antenna must be co-axial cable that connects to the common ground terminal of the receiver.
The frequency used by the remote controls is crucial for the antenna used to work properly. Today's small key ring-sized remote controls usually operate on a frequency of either 433.92Mhz or somewhere between 300Mhz and 315Mhz. Older remote controls, such as the larger cigarette package-sized ones, typically operate on a frequency of 27Mhz. It's best to use an antenna designed for the frequency used by the remote control.
Interference can be a problem even when the gate motor isn't behind any metal and has an antenna fitted. If you still only get a few meters range from your remote control, the receiver in the gate motor may be picking up interference from other wireless devices, preventing it from receiving your remote control properly unless very close. In such cases, it's better to get a Superheterodyne receiver with at least 110db sensitivity. These receivers work well with one specific frequency over a much longer distance and reject interference.
If interference persists, getting a new receiver and remote controls of a different frequency than the one suffering from interference is another option. Multi-frequency remote controls that work on three different frequencies are also available. If one frequency suffers from interference, at least one of the other two will work.
In conclusion, the range and capabilities of remote controls vary greatly depending on the system and factors such as frequency, interference, and obstacles like metal fences. Proper antenna installation and selecting the right receiver can greatly improve the performance of remote controls.