![]() ![]() The peak power handling of the same cable varies with impedance. You want to handle the highest power you can manage. According to, this isn’t the reason - it is related to using cheap steel for the center conductor instead of copper. ![]() ![]() ![]() Of course, that’s not 50 ohms, right? It is close to the 75 ohms used to carry weak antenna signals in TV systems. When you put all this together, you learn that the loss of the cable is minimized at 77 ohms for a cable with air dielectric. The impedance is also a function of the dielectric material and the diameter of the center conductor. Second, the dielectric material (that is, the insulator between the inner and outer conductors) plays a role. For coax cable carrying RF though, it’s a bit more complicated.įirst, RF signals exhibit the skin effect–they don’t travel in the center of the conductor. You generally think that thicker wires have less loss. Apparently in the 1930s, radio transmitters were pushing towards higher power levels. has an interesting article about how this became the ubiquitous match. Sure, you sometimes see 75 ohm coax, but overwhelmingly, RF circuits work at 50 ohms. If you’ve worked with radios or other high-frequency circuits, you’ve probably noticed the prevalence of 50 ohm coax. ![]()
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