Why do you need a coil in a 27 MHz car antenna?

In antenna designs, you can find a coil. Why is this coil needed there? It is called an extension coil and is used where the antenna length does not correspond to the required values, usually this can be seen in car antennas for radio stations at a frequency of 27 MHz. The normal length of the pin at a frequency of 27 MHz will be equal to a quarter of the wavelength, this is approximately 2 meters 75 cm. It is problematic to install such a pin on a car and therefore the length of the pin can be 1.5-2 meters. If such a pin is connected to the output of the radio station, not all of the output power will go to it and such an antenna will be ineffective. An extension coil is connected to the pin and now the power from the output stage of the radio station will go to the pin at maximum

If you have a short antenna, use an extension coil to fine-tune to the desired frequencies