I know that. I was pointing out that the velocity of propagation in a cable is not the same as in space and that it depends on the physical nature of the cable, including its dielectric constant but you are right that it's mostly the dielectric constant of the core.
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the OP was as
On 4/29/2019 9:49 AM, Dennis Tillman W7PF wrote:
The speed in a cable is mostly a function of the Dielectric Constant of the filling between the inner conductor and the outer shield.
The dielectric constant of the filling along with the diameter of the inner wire and the distance to the outer shield determines the impedance.
But there are many, many other considerations manufacturers have to consider. Many of those are not listed here. What is here is signal attenuation, how well shielded from interference. Other things to consider are triboelectric noise from flexing the braided shield if the cable will be carrying very small signals, group velocity, cutoff frequency, maximum power it can handle, and on and on. Take a look at this web page to get an idea of what factors are taken into account in design of a coax cable:
Dennis Tillman W7PF
From: Richard Knoppow
Sent: Monday, April 29, 2019 1:50 AM
Subject: Re: [TekScopes] My TDR Evaluation of the SG503 012-0482-00
Cable has been uploaded
Where does it show the speed of light in a vacuum? The TDR should
be calibrated to the speed of light (electricity) in the cable. For 50
Ohm cable its about 66% of c. Varies with the impedance of the cable. If
you know the physical length of the cable you can determine both its
impedance and the velocity from it.
On 4/29/2019 1:26 AM, Albert Otten wrote:
Interesting stuff Dennis! I have to look at it in more detail. Iconsider repeating these tests since I have both Tek cables, though I
don't have quality SMA-BNC adapters.
Most remarkable is the slow speed of light in vacuum in the USA ;-)--