[time-nuts] T.I. experimenting - newbie question

[Mike S]

At 09:42 PM 4/2/2011, Joseph Gray wrote...
>I'm reading 18.9 ns. The coax specs give a VOP of 66%. This should 
>calculate out to a length of 3.74 M. When I measure the coax, I get 
>3.8 M.

Your calculation is incorrect. If the velocity factor only has 2 
significant digits, the result of the calculation can only have 2 
significant digits. And, I doubt the coax manufacturer will guarantee 
the VF to 1 part in 66.

VF is the reciprocal of the square root of the dielectric constant of 
the coax insulator. 66% implies you're using a cable which uses solid 
polyethylene. A quick google for the dielectric constant of 
polyethylene shows a range (2.2-2.4 depending on the source). That 
would be a VF range of .67-.65.

Working your numbers, I get a length of 3.7-3.8 m.