At 11:36 PM 7/13/2005, Al Toothaker wrote:
>Wouldn't the different electrical lengths indicate that the cable
>manufacturing process is not consistent? Any spec on a cable has a
>tolerance and though they may wander in performance, it could still meet
>their specs.
The velocity factor in foam coax is the most difficult thing to control, since
it is a function of the percentage of air bubbles in the dielectric. Some
manufacturers specify it for a range of values -- such as 0.78 -- 0.82 VF,
others just give a nominal value.
Solid dielectric is much more controllable, but I even measure the actual
phase shift for each delay line of solid dielectric coax, if the
application is critical.
And with foam coax it is MANDATORY to TUNE (trim) each delay line to
the correct electrical length.
--John W0UN
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