[Elecraft] Small QRP antenna

[Don Wilhelm]

Walt,

I differ, antenna wires do have a velocity factor to consider.  I built 
a 6 meter Moxon beam for my grandson out of insulated wire, and the 
resonant frequency was considerably low.  Stripping the insulation from 
the wire brought its resonance point up to what was expected.
The only reason was because the velocity factor for the insulated wire 
was less than that of non-insulated wire.

73,
Don W3FPR

On 12/29/2016 6:33 PM, Walter Underwood wrote:
> This is quite likely overly pedantic, but “velocity factor” is a characteristic of transmission lines. Interestingly, it is independent of frequency (up to the limit of the dielectric). It depends on the geometry of the line and the dielectric material.
>
> Antennas don’t have a velocity factor. The shortened elements are caused by capacitive loading against (RF) ground. There is a percentage of the free-space electrical length due to capacitive loading, but it is not a velocity factor. I don’t think this has a snappy shorthand other than “electrical lengthening due to capacitive loading”.
>
> For example, dipoles with capacity caps on the ends, like the N6BT designs, don’t change the velocity of propagation along the elements. They use massive capacity loading on the ends (the high-voltage part of the dipole) to shorten the elements.
>
> http://www.force12inc.com/products/sigma-20-hd-20-meter-heavy-duty-vertical-dipole.html <http://www.force12inc.com/products/sigma-20-hd-20-meter-heavy-duty-vertical-dipole.html>
>
> OK, overly pedantic mode off, plus I’ve nearly hit the limit of what I remember from my fields and waves class decades ago. I was pretty happy to get a B- in that class.
>
> wunder
> K6WRU
> Walter Underwood
> CM87wj
> http://observer.wunderwood.org/ (my blog)
>