Transmission Line's Electrical Wavelength

Do you want to know the true wavelength of those transmission line?

The true wavelength of a transmission line is the electrical wavelength, and not the physical wavelength of the transmission line. The electrical wavelength is depended on the velocity factor of the speed of light of the transmission line, and the velocity factor depends on what dielectric constant of insulated material between the 2 conductors of the transmission line.

Insulated material	Velocity Factor	Dielectric Constant
Polyethylene solid	66.7%	2.25
Teflon solid	70%	2.1
Polystyrene solid	60.8% to 64.5%	2.4 to 2.7
Polypropylene solid	65% to 67%	2.2 to 2.36
Polyethylene Foam	74 to 85% Depending on how much air bubbles in the foam.	1.38 to 1.8
Air	99.9%	1.00058986
Vacuum	100%	1

So the higher the dielectric constant of the insulated material of the transmission line, the lower the velocity factor, the shorter the electrical wavelength of the transmission line, and higher the loss per long length of transmission line. The lower the dielectric constant of the insulated material of the transmission line, the higher the velocity factor, the longer the electrical wavelength of the transmission line, and lower the loss per long length of transmission line.

Here is the formula of the physical wavelength of electromagnetic radiation:

Table of Definition
f =	Frequency in MHz (Megahertz)
l =	Wavelength in feet

l = 984 / f

Here is the formula of the electrical wavelength of a transmission line of certain velocity factor:

Table of Definition
f =	Frequency in MHz (Megahertz)
l =	Electrical wavelength with the velocity factor of transmission line in feet.
VF =	Velocity factor of the speed of light of transmission line in percent

l = 984 x VF / (f x 100)

Here is the formula of the electrical half wavelength of a transmission line of certain velocity factor:

0.5l = 492 x VF / (f x 100)

Here is the formula of the electrical quarter wavelength of a transmission line of certain velocity factor:

0.25l = 246 x VF / (f x 100)

Here is the formula of the electrical one eighth wavelength of a transmission line of certain velocity factor:

0.125l = 123 x VF / (f x 100)

For Example:

A polyethylene solid insulation in the transmission line has a velocity factor 66%, and you want to know the electrical quarter wavelength of a transmission line at 27.185 MHz at CB channel 19:

246 x 66.7% / (27.185MHz x 100) = 6.036 ft

So every multiple of a quarter wavelength polyethylene solid transmission line is 6.036ft, 12.70ft, 18.108ft, 24.144ft, 30.18ft, or 36.216ft, or longer every multiple of 6.036ft.

Every odd multiple of a quarter wavelength polyethylene solid transmission line is 6.036ft, 18.108ft, 30.18ft, or every odd multiple is 1 x 6.036ft, 3 x 6.036ft, or 5 x 6.036ft.

Every even multiple of a quarter wavelength polyethylene solid transmission line is 12.70ft, 24.144ft, 36.216ft, or every even multiple is 2 x 6.036ft , 4 x 6.036ft, or 6 x 6.036ft.

For Example with the Teflon Transmission Line:

A Teflon solid insulation in the transmission line has a velocity factor 70%, and you want to know the electrical quarter wavelength of a transmission line at 27.185 MHz at CB channel 19:

246 x 70% / (27.185MHz x 100) = 6.334ft