US frequencies for garage door remote ctls. is somewhere between 310 - 320 mHz. Remotes get abused and used alot so visually inspect the circuit board for any hairline cracks, poor solder joints, or loose lead components. Also clean the switch contacts and assure the battery contacts are clean as well. Many remotes employ a small trimmer capacitor to tune the circuit, but unless you have a service manual you could detune it, making things worse. Again, try repositioning or lengthening the antenna wire. In one instance for me the antenna wire improved reception by stapling it to the drywall ceiling. In another instance, it worked well by wrapping it several turns around the AC power cord to the door opener itself.