Coils on antennas

[Thatsclear]

Why do some antennas have coils on them and some do not? What does this do? I can't find anything explaining it. Thanks.

 

[doctordialtone]

Why do some antennas have coils on them

Coils, or "Loads" electronically alter the length of the antenna.

Read here:

Antenna loading coil: Everything You Need to Know

An antenna loading coil is an inductor placed in series with an antenna element in order to lower the antenna’s resonant frequency. A standard dipole antenna is resonant if constructed with a length of one-half wavelength. A vertical antenna (effectively half ... Read More

www.amateur-radio-wiki.net

Loading coil - Wikipedia

en.wikipedia.org

 

[Ubbe]

It could also be an impedance match that connects one part of the antenna, that might be of a 3/4 wavelenght, to a 1/4 wave part. It could also be a phase shift coil to make different antenna parts work together in phase and add gain.

/Ubbe

 

[n5ims]

They're also used to pass some frequencies and block others to form a multi-band antenna.