Er.
The quote refers to a transmission line - not an antennae.
The correct  length for an antennae is very close to the calculated free
air value -but may be changed by loading coils, "top hats" and matching
networks etc.
If you use a transmission line e.g. coaxial cable as part of the matching
network then you do need to take its velocity factor into account for this
.
This velocity factor is a result of the capacitive and inductive properties
of the materials (pretty much entirely the diaelectric coefficient of the
insulator) in the transmission line. Solid polythene gives a factor of
about 0,67, expanded polythene a ration of up to about 0.84.  Since an
antennae is insulated by air, the velocity factor is close to 1.00.

Richard P











Actually - the shorter length maybe more correct - the speed of the wave
(the 3 x 10^8) will be lower in a wire than in free air - which looks to be
the figure used here. This means we end up with a shorter wavelength in a
wire.

<Quote>A radio wave in free space travels with the speed of light. When a
wave
travels on a transmission line, it travels slower, travelling through a
dielectric/insulation. The speed at which it travels on a line compared to
the free-space velocity is known as the "velocity factor".

Typical figures are:
Twin line  0.82,  Coaxial cable 0.66,  (free space 1.0).  </Quote>

http://www.amateur.radio.org.nz/nzart/examinat/amateur%20radio%20study%20guide/Course%20Files/Transmission%20Lines/STUDY%20NOTES%20-%20TRANSMISSION%20LINES.htm


Also

http://www.guerrilla.net/reference/antennas/2ghz_collinear_omni/

Using these figures we would get a 1/4 wavelength of ...

3x10^8 / 434x10^6
------------------------- x 0.85 (approx)   = 14.6 cm
            4


>>> dpharris@TELUS.NET 05/14/02 01:33PM >>>
Hi-
Except you have 434 MHz modules, so you want: 3x10^8/434x10^6 = 0.69, so
you want
a 0.69/4 = 0.173 meter = 17.3 cm 1/4 wave whip.  I think it needs to be
straight.
Hey, my 12 cm piece of wire seems to work fine, gues I should extend it.
David

Gary Neal wrote:

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