What happens as the frequency of a signal in coaxial cable is increased?

All coaxial cables resist the flow of radio frequency energy to some extent, converting a portion of your signal into heat. As the frequency of the signal increases, these resistive and dielectric losses naturally increase. For example, a length of coax that works perfectly well with very little loss on the 80-meter band (3.5 MHz) might absorb almost all of your signal on the 70-centimeter band (440 MHz). It is important to note that the characteristic impedance of a coaxial cable (such as 50 ohms) is determined by its physical construction, specifically the ratio of the inner conductor's diameter to the outer shield's diameter and the type of insulation used. Therefore, the characteristic impedance remains constant and does not change with frequency; only the signal attenuation (loss) changes.