Tuned Antennas?

[Neutrino222]

Is the length of a mobile antenna the only factor that determines its tuning?

Can there be anything else added to the internals of the antenna that aids its tuning?

For example, I have a Mitex radio and it's antenna is tuned to 400-470 mhz. Going by this logic, my SDS100 antenna is the same length, so would it perform in the same way to a tuned antenna in that part of the radio spectrum?

If so, why is the length important?

 

[kb5udf]

A myriad of other factors can come into play including:
base loading coil
center matching coil
top matching device/coil
diameter of radiating element
the environment near the radiating element
ground plane

Length matters because it is a primary parameter impacting resonance. Length is often determined
with reference to wavelength. Regarding your specific antenna, some antennas are not designed to take t/x
power; they may be intended as rx only. Length alone does not guarantee 2 antennas will be identical in
performance and resonance.

I would add that most commonly used handheld and mobile antennas are based on the dipole antenna.
There is a formula you will commonly see for the length of a dipole:
length = 468/frequency in MHZ

 

[Ubbe]

Unidens antenna are multiband antennas and has one coiled up antenna element of a helix type tuned to about 155Mhz and will work at 3 times the frequency at 470Mhz and another antenna element for 800MHz.

The shorter you make an antenna the less RF energy it will capture from the air waves, if it's still tuned to the same frequency by adding coil impedance.

/Ubbe