What is a filter?

A filter is in this context a device that is cutting out the background noise of produced by other devices, the environment, our solar system, and all living beings. A filter is essential for optimal operation of antennas, and other radio equipment including amplifiers and trancievers.

An antenna is essentially a device sensing the electromagnetic landscape it is moving through. They can be designed to pick up specific frequencies of waves, in specific polarization directions. The material used, it's magnetization, it's orientation, and placement all affect its effectiveness. For optimal effectiveness and tranceiving capabilities, it must be ensured that the antenna is impedance matched to the circuit it's connected to, it must also be placed such that interference is minimized. The quality of cables and filters removing out of band signals must also be employed for reliable performance.