How well you hear depends on the radiation pattern of an antenna. A 102" whip, a 1/4 wave length antenna, has one pattern. Longer antennas (to a point) tend to have larger patterns, or patterns that cover more area. Antennas that are shorter than the 1/4 wave but use a loading coil to make it 'seem' like a 1/4 wave, have a slightly lesser area of coverage than the 'full sized' antenna. It's a function of the overal length that determines pattern shape and 'size'. The shorter antenna may load just like a 1/4 wave (or a 1/2 wave, or a 5/8 wave or whatever) but just will not have the same radiation patter as the full sized one, always less. Now, having said all that (and it's a fact), a full sized antenna has practical draw backs. Depending on just how tall/long the full sized antenna is, it'll probably be a huge P.I.T.A. on a mobile cuz it's gonna be in the way at least part of the time. Or it'll sway at speed and give different loading characteristics. So, shortened antennas are worth the trouble even if slightly less than 'perfect' (whatever the @#$$ that means anyway).
Coils do not render any miraculous properties to antennas. At most, they will make the thing load like the real-live size would. At worst, they introduce losses that counteract any so-called 'gain' claimed. (Ain't no gain to it, that's a sales hype.) It's all a matter of adding the proper reactance to a too-short antenna to make the radio think it's the real thing. Sorry if that hurts anyone's feelings, but it's true none the less. They do look impresive though, don't they? Another feature of coils is that they tend to indicate a 'broader' usable frequency range. The key words there are "tend" and "indicate". The actual usable frequency range is actually less than a 'full sized' antenna when you consider efficiency, not what the SWR meter says. So, that aspect is another 'sales hype' thingy. The thing to do is take the 'practical' aspects in to consideration. You can just see your self driving down the street with a 5/8 wave antenna (about 22 feet?) on the car, right? So shortened antennas, any antenna with a loading coil, certainly do come in handy. Don't attribute any miraculous properties to them though, just ain't gonna happen.
That help any?
- 'Doc