| Electronics > Beginners |
| Difference between coax cable and shielded cable |
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| tautech:
Coax, shielded, who cares ? Such generalization should be chastised here on EEVblog ! :P It's their intended application that really matters and I'll just drop this here for you all to pick at: Source PDF attached. |
| radiolistener:
The difference is insulator material and insulator geometry. Coax cable has specific low loss insulator material which size is stable along entire cable. It leads to stable relation between inductance and capacitance (impedance) along the cable length. Usual shielded cable may use more cheap insulation and may not keep insulator geometry along cable length. It leads to variable relation between inductance and capacitance (impedance) which is very bad for high frequency signals. Such impedance variation leads to signal reflections and standing wave in the cable. The RF energy is flowing in the insulator between central conductor and braid. This is why insulator properties and geometry are very important for coax cable. |
| tautech:
Well isn't coax by definition a shielded cable ? Shielded by braid. Then of course there's coax that's foil shielded and braid shielded too. :P |
| tooki:
--- Quote from: Berni on October 17, 2019, 05:21:51 am ---Nothing wrong with replacing RCA with BNC. The RCA cables used for composite video are 75 Ohm and the BNC cables found in a TV studio are also going to be the 75 Ohm kind. There is actually a problematic combination of 75 Ohm and 50 Ohm BNC connectors. I forgot what way around it is but i think plugging a 75 Ohm male into a 50 Ohm female BNC can damage one of the connectors because some of the dielectric inside them gets in the way. --- End quote --- Indeed, I am quite confident that most people don’t even realize there are different BNC connectors for 50 and 75 ohms. I certainly didn’t until I read about it here on the forums, even though I had a teeensy tiny bit of experience with both kinds, having used 75 ohm ones in broadcast video and on some 90s high end computer displays, and 50 ohm on old ThinNet Ethernet. But that was always with premade cables, and I knew enough to not try to feed Ethernet right into the RGBHV inputs of a display! :p |
| Berni:
Actually i got it wrong. Its mechanically fine to mix 50 and 75 Ohm BNC connectors as the only difference is that the 75 Ohm have less dielectric inside. Its the 75 Ohm N connectors that are dangerous because the center pin has slightly different dimensions and as a result plugging the larger 50 Ohm male into a 75 Ohm female can result in connector damage. |
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