In a sence the parasitic inductance of a resistor is in most cases so irrelevant that in the theoretical introductions to electronics it is fully ignored. One really needs the theory to guide the practice, and one really needs the practice to guide the theory.

It’s the same difference between theory and practice. Should I view inductors as having inherent resistance?īoth the “yes” and “no” perspectives are important. Should I view resistors as having inherent inductance? I like your comment, and I’m definitely not trying to school you, what I’m going to write is what I wish people had written for me to read whenever this question came up: are transmission lines vs antennas now balanced or unbalanced? the perspective I will elaborate is not very popular! Posted in Radio Hacks, Slider Tagged 50 ohm, cable, Coax, impedance Post navigation If you are more interested in coax terminations, we got you covered there, too.

If you want to learn more about RF design, you could do worse than watch workshop (see below). The mean between 30 and 77 ohms is 53.5 ohms. So a cable that has least loss at 77 ohms, also has maximum power handling capacity at 30 ohms. 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.

50 ohm smith chart