I did not get into the "technical" aspects in my last post because I was too lazy
But it goes something like this......
The tighter the waves, ie the bigger the Mhz, the more penetrating they are. Ie, the will go through solid objects easier with less distortion. This is one reason why microwave is used in mobile phone technology. This obviously has little bearing in RC
So the second way to make a wave more powerful is to make it stronger, ie. have a larger wave amplitude which requires an amplifier. Better radios may have a degree of amplification for a clearer signal. I am not sure however.
Another way to get better reception is to make the receiver less prone to noise (shielding) and to make the transmitters aerial and the receivers aerial the correct length. There is actually a scientific forumula for calculating how long an aerial should be for a given frequency for maximum signal strength.