1/2 of a wavelength inside of 72 ohm RG-59 TV coax
 

In http://www.scannerway.8m.com/cgi-bin.../antennas.html it says
(eg. 2953/144Mhz = 20.5 inches). This is 1/4th of a wavelength...
(eg. 8,859/144Mhz = 61.5 inches) This is 1/2 of a wavelength inside of 72 ohm RG-59 TV coax.
I don't get it, doesn't he mean 3/4? And isn't the wavelength the same
within or without? I suppose aside from this, the instructions are good, no?

On Tue, 30 Dec 2003 01:08:53 +0800, Dan Jacobson
wrote:

In http://www.scannerway.8m.com/cgi-bin.../antennas.html it says
(eg. 2953/144Mhz = 20.5 inches). This is 1/4th of a wavelength...
(eg. 8,859/144Mhz = 61.5 inches) This is 1/2 of a wavelength inside of 72 ohm RG-59 TV coax.
I don't get it, doesn't he mean 3/4? And isn't the wavelength the same
within or without? I suppose aside from this, the instructions are good, no?

Hi Dan,

You've forgotten the velocity of propagation inside a transmission
line is different from a wire in free space (the author suspects it is
66% of free space).

The outside electrical dimension of coax is not the same as wire in
free space either, as it has a thick dielectric covering (and there
are variations for conductor thickness as well). This is why the
common advice of cut long and tune to resonance so often attends
construction projects.

73's
Richard Clark, KB7QHC