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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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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Generally, cost. A thin stiff wire like a car antenna mounted on a fender uses much less metal that a thin hollow tube that retracts into the fender. The wire is more resistant to damage since it flexes instead of bending and snapping off like the hollow tube will.

For larger antennas like house aerials on a roof, having a hollow tube may be preferable since the tube is stiff and will hold itself up, whereas a thin cable or wire requires a guy wire to hold up the floppy end straight. If there is no tree or support structure nearby you need to build and install one which is more expensive than using a self supporting tube.

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.

Mostly it’s frequency.

Frequency is inversely proportionate to wave length. Wave length determines antenna length.

Old AM radios required a big antennas. You probably seen them outside, they can be several hundred feet tall. The whole tower is an antenna.

FM radio antennas are a lot smaller. They look like little half circles mounted on the tower.

Wifi antennas are even smaller. The whole wave length is almost 5 inches. So you can put a tiny wifi antenna in your phone and it doesn’t take much space.