Why did radio aerials switch from using metal telescopic tubes to thin cables? And what’s the advantages and disadvantages of each design?
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It doesn’t really matter if the antenna is a wire, or a telesopic tube. the lenth is important and the tube design is only to make the antenna retractable for convenience.
The length of an antenna is related to the wavelenth/frequency you can (efficiently) receive.
Idealy the length of your antenna is exactly the same as the wavelength.
Because of harmonics, you can get away with 1/2th of the wavelength, 1/4th of the wavelength, etc… Smaller antennas have weaker reception and therefore give a weaker radio signal. 1/4th wavelenth was a good size/quality antenna for a long time.
Because of advancements in ampliciation technology, even weaker radiosignals can now be used and therefore the size/lenth of the antenna can also be reduced.
Because the antenna can now be smaller, it doesn’t make much sense to make it retractable anymore. (Too much costs for not enough benefit.) Some cars even have this antenna wire as a conductor stuck to one of the windows.
Car antennas are now also no longer passive wires, but contain active components, making them even smaller, such as these sharkfins on the roof.
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