We use 173MHz transceivers to reduce the frequency as much as possible (which reduces losses) without making the antenna too large.
However a helical antenna is based on a quarter wavelength wire (about 43cm in air) coiled into a smaller space. Glaciers have a dielectric constant which is about 2.2 and radio travels at about 1.6 m/ns. This means the helical antenna can be about half the air size. Of course in practice the environment varies its dielectric constant so optimal tuning is rare.