what are the factors that would vary the speed of RF signal?Thank you

 

Do you mean, for example, what determines the velocity factor of a co-axial cable?

 

Result from AppCAD simulation for coax with velocity factor less than free space ....

Propagation velocity in this coax is about 0.7 velocity of light.

The main determinant here of velocity factor is the relative permittivity of the dielectric material. If the dielectric were "free space" then the velocity factor would be (notionally) 1.

 

what are the factors that would vary the speed of RF signal?Thank you

The speed of an R.F. signal is dependent on the dielectric constant of the medium it's traveling through.

This is the main means of low frequency radio signals bending around the Earth (true groundwave). A vertically polarized wavefront in contact with the surface of the Earth follows the surface because it has a higher dielectric constant...so the wave bends toward the slower medium.

eric

 

This is also true of light and the parameter of interest is the index of refraction. Look at a rod in a glass of water and notice the effect of light bending.