50 ohm and 75 ohm characteristic impedance

Why do 50 ohm get to be the standard RF transmission line impedance in the mobile communication systems, but 75 ohm is for CATV?

Quoted from:
http://www.epanorama.net/documents/w...coaxcable.html

Regards,
IanP

You say the characteristic impedance of the coaxial cable. But I point to the impedance of PCB. E.g. the intermidiate matching between the two amplification stages. The microstrips of 50 ohm are usually used in the radio communication.

The attenuation of a coaxial cable is the lowest when impedance is about 77 ohm. Further a dipole antenna has a real impedance about 73 ohm. Therefore for CATV, where attenuation is important, a cable of 75 ohm seems a right choice.
Anyway, another important feature is the power handling capacity; it is possible to show that the maximum power trasmission in a coaxial cable is for an impedance of 30 ohm. A good compromise to obtain a good attenuation and a good power handling capacity is 50 ohm; this value is used for application where the power trasmission is important.
For more details you can see https://www.edaboard.com/viewtopic.php?p=166750#166750

Regards