The Antenna
For example, the wavelength of the amateur radio 145 MHz band is approximately
2 metres so an antenna described as 'full wave' would be 2 metres in length,
an antenna described as 'half wave' would be 1 metre in length, and so on.
Similarly, a frequency of 98 MHz, in the domestic broadcast FM band, has a wavelength of approximately 3 metres.
The wavelength (in metres) =
300 divided by the frequency (in MHz).
Obviously, a radio is designed to cover a range of frequencies so the length of an antenna can only be a rough dimension, usually cut somewhere near the center of the band. In any event, as a filter, it would be nowhere near 'fine' enough to remove unwanted frequencies except, maybe, those tens of hundreds of MHz away.... But it is a start.