Topband: Coax velocity factor

W0UN -- John Brosnahan shr at
Wed Mar 28 06:48:23 EST 2007

At 06:43 28-03-07, EP Swynar wrote:
>On 27th March Charles wrote...
> > Every time I get the same results: VF=84%.  This just seems a tad high to
>me, especially when 75% is the published value for RG-6, though I know the
>VF of foam cable is higher. Anyone else get similar results when checking
>this type of cable?

The VF of solid-dielectric cables is much easier to control than that 
of foam cables.
For a solid cable the VF is just a function of the properties of the 
dielectric material.
But for FOAM cables the VF is a function of the properties of the 
dielectric material
AND the percentage of air bubbles in the material.

Reel to reel variations can be quite large in foam cables and even 
variations in
the same reel can be significant.   EVERY phase-sensitive cable made from foam
dielectric must be tested individually.

--John    W0UN

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