What method can be used to reduce the inductance of an antenna coil?

Reducing the number of turns in an antenna coil is a valid method to decrease the inductance. Inductance is directly related to the number of turns in a coil—more turns increase the magnetic field, which in turn increases inductance. By reducing the number of turns, you lessen the amount of magnetic field produced, thereby reducing the inductance of the coil. This is particularly important in antenna designs, as proper tuning and matching of the antenna's impedance can significantly affect performance in transmitting and receiving signals.

Increasing the wire gauge, while it can influence resistance and the quality factor of the coil, does not directly affect inductance in a predictable manner. Adding a choke typically increases inductance, as a choke is designed to block high-frequency AC while allowing low-frequency signals to pass, fundamentally relying on inductance. Decreasing the coil diameter would generally increase the inductance, as a smaller diameter can lead to tighter magnetic coupling and thus a stronger magnetic field, which increases inductance.