[time-nuts] Safely getting the electrical length of a connected antenna feedline

Scott McGrath scmcgrath at gmail.com
Fri Aug 12 09:04:09 EDT 2016

Because Velocity Factor determines the time it takes a EM wave to traverse the cable it ALSO shortens the wavelength by the same amount relative to free space this is why coaxial cables can be used as delay lines and why when cutting resonant sections of coaxial cable the Velocity Factor must be known

Content by Scott
Typos by Siri

> On Aug 11, 2016, at 2:56 PM, Bob Stewart <bob at evoria.net> wrote:
> Why is velocity factor an issue?  Aren't we only interested in the electrical time from one end of the coax to the other?
> Bob
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>      From: Didier Juges <shalimr9 at gmail.com>
> To: Bob Albert <bob91343 at yahoo.com>; Discussion of precise time and frequency measurement <time-nuts at febo.com> 
> Sent: Thursday, August 11, 2016 1:20 PM
> Subject: Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
> I used the PPS from a Thunderbolt (fast rise lime, low rep frequency, was handy) and a digital storage scope and a couple of resistors to make a reflectometer based on this experiment:
> www.ko4bb.com/getsimple/index.php?I'd=coax-cable-impedance-matching
> You can very clearly see a 50 ohm/75 ohm mismatch.
> The biggest variable will be the velocity factor.
> Didier KO4BB
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