John Tvedte wrote:
Ok,

w = c / f; so w= 1 wavelength - use c = speed of light (in air)

s = 0.487 w ; where is the 0.487 from?

The speed of light in air isn't the number to be using. EM waves propagate
at slower speeds in different media. Normally this speed is expressed as
a "velocity factor" which indicates what fraction of the speed in vaccuo