Relationship between frequency and other signal characteristics
As a signal travels through the air it loses it's energy.


You might be misunderstanding something here. When we talk about signal power depending on distance from the transmitter like 1/R2, the reason is that as you get further from the transmitter, the available energy is spread across a larger area (the area of a sphere around the transmitter with radius equal to R), not because energy is lost.

There is a small loss to heating the air (or particles in the air), but this is usually not as important as the 1/R2 effect.


  Does frequency decrease due to losing energy? 


No. When we say \$E=h\nu\$, we are talking about the energy of a single photon. When we talk about a signal losing energy, if we look at it from the particle point-of-view, it loses energy by reducing the number of photons, not by the individual photons losing energy. As the previous answer said, in the classical view this is equivalent to the EM wave amplitude being reduced.