Originally posted by

**joni1101**View PostThe electromagnetic field of coax is totally enclosed inside the space between core & shield, and this space is totally filled with insulation. The speed of propagation along coax is therefore determined solely by elocity factor of the dielectric material in the coax.

The antenna wire's electromagnetic field is un-enclosed, and is in a space of which the wire insulation constitutes negligible part (thickness wise). Its Velocity Factor is therefore:

VF

_{eff}= (VF

_{1}x t

_{1}+ VF

_{2}x t

_{2}) / (t

_{1}+t

_{2})

where

VF

_{1}is velocity fctor of insulation, say 0.66

t

_{1}is thickness of insulation say, 2 mm

VF

_{2}is velocity fctor of air = 1

t

_{2}is thickness of air say 10 km **

***The thickness of air in which electromagnetic field of antenna wire exists is the distance between transmitting antenna and the receiving antenna, hence it is in tens or hundreds of kilometers.*

Hence VF

_{eff}= (0.66 x 0.000002 km + 1 x 10 km)/(0.000002 km+10 km) = 10.00000132 / 10.000002 = 1

Electromagnetic field of Antenna

Occupies space between transmitting and receiving antennas

Electromagnetic field of a Coax cable

Totally confined in the space between core and shield i.e. totally inside the core insulation

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