Why do we need coaxial cables for TV signal transmission, what would happen if we would just use a „normal“ cable instead?
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To act as Transmission lines in the center of the cable thats surrounded by lots of shielding material to block out electromagnetic waves traveling around in the air
What’s a “normal” cable? I mean, when I think of cables, coaxial *is* normal. It’s the way TV and cable and satellite signals have been moved for, like, 50 years or more. They’re good for long ranges with very little signal degradation (beating CAT5 and CAT6), they’re simple (only goes in one way!) to use (beating USB1 and 2), they’re simple to repair (snip, snip, pull, press, pull) (beating USB3 and Ethernet), and they’re durable (beating twisted pair RJ45, aka telephone wire). So…why wouldn’t we use them?
The precise distance between the center conductor and the shield ensures that the impedance of the wire stays consistent so that the signal will not be reflected back to the source. The outer shield also shields the center conductor from interference from other wires or radio transmissions in the area. The medium between the center conductor and the outer shield is also specially selected to allow the magnetic field made by the center conductor to form without any resistance.
There are other signal wires then coaxial wire. For higher frequency signals it is common to use waveguides which are essentially empty tubes where the radio signal bounces around inside. You may also have seen ladder lines where there are two parallel conductors in perfect balance. Similarly modern technology tends to use twinax which can be described as a combination of a ladder line and a coax cable with two center conductors and an outer shield.
If you use any odd cable to transfer signals then you will experience a lot of losses. Most of the signal will not get through the wire. And you will experience interference, both from other things to the signal but also from the signal to other things. For examples the TV signal might not work if the wire is next to the wire for your USB charger and you might see LED light flicker to the TV signal if the wires are close to each other.
Most cables are used for electrical signals. There is a significant amount of power behind the signal lots of electrons are flowing. Coax cables are used for much weaker signals where the sender can’t force the signal to be the shape they want by just using a lot of power. So regular cables for electrical, connections coax cables for gently guiding radio waves.
Trying to actually eli5 so it’s not a complete explaination but touches on the common everyday usecase.
“Normal cable” is a meaningless term. There is no normal or base type. Every cable is designed for a specific purpose and is “normal” for that application.
In the case of coax it has a lot of shielding to prevent interference in the sugnal.
I am not sure why this question is being down-voted.
If somebody thinks that this is an obvious question, consider that computer networks started with using [thick coaxial cable for wiring](https://en.wikipedia.org/wiki/10BASE5), then gradually moved to cheaper thinner coaxial cable, and eventually to the [cable made from twisted pairs of wires](https://en.wikipedia.org/wiki/Twisted_pair), which is not too far from what the OP may call “normal” cable — though it is much more carefully made than electric cords for appliances. (Note that modern computer networking cables work at similar frequencies to those used for TV transmission.)
This shows that despite its many excellent features, coaxial cable is not preferred for all applications. There is really no simple, clear-cut answer to the OP’s question, even though many things that have already being mentioned in the comments — regarding low interference, controlled impedance, availability of tools and connectors to work with coaxial cables — are all true. These factors all contribute to its popularity in many, many applications.
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