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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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.
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