Why 50 Ohms?

Have you ever wondered why almost all RF and microwave systems have 50-Ohm characteristic impedance? Find out in 2 minutes.
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[@clems6989]

Cable companioes went with 75ohm to minimize losses because they extend such long distances. Radio mostly went 50ohms because its a great tradeoff between loss and cost...

[@chuckcrizer]

No, cable companies went with 75 ohm cable because that was already in common usage for all modern TV systems, households and buildings.

[@clems6989]

@@chuckcrizer Lets split hairs. Cable companies followed TV which had settled on 75Ohms for the reason i stated.. Geezus !

classic engineering round off

[@bigfranz1709]

With engineering round off 😂

[@martinvollderpro]

🤣🤣🤣

[@yootoobvyooer]

How did they come up with those graphs, experiment or via Maxwell's equations? If equations, how were they derived?

[@quaxys_academy]

This is a great question. The derivations for loss and power handling capability can be found using the coaxial cable equations in the following links.
This link derives the formula for the loss:
phys.libretexts.org/Bookshelves/Electricity_and_Magnetism/Electromagnetics_II_(Ellingson)/07%3A_Transmission_Lines_Redux/7.03%3A_Attenuation_in_Coaxial_Cable
This link derives the formula for the power handling capability:
phys.libretexts.org/Bookshelves/Electricity_and_Magnetism/Electromagnetics_II_(Ellingson)/07%3A_Transmission_Lines_Redux/7.04%3A_Power_Handling_Capability_of_Coaxial_Cable

[@zedcarr6128]

This begs the question, why is there also 75 Ohm coaxial cable for video, TV etc?

[@quaxys_academy]

Thanks for your question. There are a few reasons for using 75 Ohms.

1. As demonstrated in the video, a 73-ohm characteristic impedance results in minimal attenuation. Therefore, when dealing with weak signals from an antenna or an analog video link, 75-ohm cables are preferred.
2. A half-wave dipole antenna used in TV receivers has an impedance of 73 ohms at its resonant frequency, making it well-matched to a 75-ohm cable.
3. Moreover, a folded dipole antenna used for TV receivers has an impedance of 300 ohms. So, by using a 4:1 balun, a 75-ohm cable provides an excellent match.

[@zedcarr6128]

@@quaxys_academy Thank you so much. 😲 Nearly 40 years I've been an engineer in electronics, electrics and mechanics, and this simple fact has never been explained to me, or have I ever bothered to ask the question. This is one of those nuggets of knowledge that is mind blowing. 😊 Subscribed!

[@alansalari6319]

​@@zedcarr6128Thank you for asking this important question.

[@yootoobvyooer]

How did they come up with those graphs, experiment or via Maxwell's equations? If equations, how were they derived?

[@quaxys_academy]

We have addressed your question below.