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All of the CATV industry runs on 75 ohm systems, while most of the rest of the radio world uses 50 ohms.

Why was this standard chosen?

I was wondering this because good quality RG6 cable can be obtained everywhere for very little, compared to decent quality 50 ohm cabling.

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  • \$\begingroup\$ Some insight is in Andy's answer:electronics.stackexchange.com/questions/350451/… \$\endgroup\$ – glen_geek Mar 30 at 17:49
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    \$\begingroup\$ I'm not sure if I should say "a substantial minority" or "enough so that it's known" -- but there are radio amateurs who use 75 ohm transmission line for this reason. If you're going to run an antenna tuner anyway, and if you're going to build your own antennas anyway, then it's not a bad way to get a bit more bang for the buck. \$\endgroup\$ – TimWescott Mar 30 at 18:11
  • \$\begingroup\$ @TimWescott specifically, this: qsl.net/g4hbt/dipole.htm antenna specifies a 75 ohm line. I finally understand why. \$\endgroup\$ – hjf Mar 30 at 18:13
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    \$\begingroup\$ It was 75 ohms for RF signals before cable TV was a "thing". I've always figured it was the cable manufacturers, so they could force you to buy two spools of cable instead of just one. And the connector manufacturers, so they could sell you two different sizes of connectors. \$\endgroup\$ – Hot Licks Mar 30 at 19:07
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    \$\begingroup\$ Possible duplicate of How is transmission line impedance selected? \$\endgroup\$ – Dmitry Grigoryev Apr 1 at 11:17
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How is transmission line impedance selected? explains why transmission line impedance matters.

The CATV industry deals with low-level signals, so it cares ONLY about loss and not at all about power-handling. That's why they chose 75Ω transmission lines.

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  • \$\begingroup\$ Awesome! I didn't know that thing about power, and now I also understand why NOAA reception turnstile antennas specify 75 ohms too! \$\endgroup\$ – hjf Mar 30 at 18:01

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