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speed u = sqrt(1/LC); L=inductance per unit length, C=capacitance per unit length

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f95toli

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However, the speed of propagation is not related conductivity of the metal (the conductivity is only related to the losses in the line) but to the dielectric constant of the dielectric (the insulator); the speed of propagation is roughly [itex]1/\sqrt\epsilon[/itex].

Remember that the wave in a transmission line is not actually traveling in the metal (at high frequencies the skin depth is very small) but in the dielectric.

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vanesch

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1) the inductance per unit of length of the conductors

2) the capacitance per unit of length between the conductors.

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Can anyone refer me to a book or website with a discussion concerning this subject?

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isn't there also the resistance per unit length and possibly a leakage conductance (between the two conductors) per unit length?

1) the inductance per unit of length of the conductors

2) the capacitance per unit of length between the conductors.

well (looking at the wiki page), maybe you're completely right, but i thought that R and G played a role in determining wave velocity in a lossy transmission line. but, it appears (not solving the diff eq myself) that it's just C and L.

maybe start here with the Telegrapher's_equations. the book or books i have on the topic are soooo old (35 years) that i can't recommend since they must certainly be out of print.Can anyone refer me to a book or website with a discussion concerning this subject?

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There are only really three types of dielectric (insulator) used in coax cable. Air where the inner conductor is supported at regular intervals, PE (Polyethylene) or Teflon (PTFE). PE is by far the most common.

The velocity factor for PE is about 66% of the speed of light. PTFE it is about 70%. Some coax cables use foam or semi-air spaced PE and the velocity factor will be higher.

http://www.nr6ca.org/vf.html [Broken]

Foam or air are used mainly to allow a larger centre conductor to be used for the same impedance in order to reduce loss. Loss per length increases with frequency due to the skin effect. The current travels in a thin skin near the surface of the conductor and the depth of this skin reduces as you go up in frequency.

The velocity factor for PE is about 66% of the speed of light. PTFE it is about 70%. Some coax cables use foam or semi-air spaced PE and the velocity factor will be higher.

http://www.nr6ca.org/vf.html [Broken]

Foam or air are used mainly to allow a larger centre conductor to be used for the same impedance in order to reduce loss. Loss per length increases with frequency due to the skin effect. The current travels in a thin skin near the surface of the conductor and the depth of this skin reduces as you go up in frequency.

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mheslep

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1. Velocity factor, the speed of electromagnetic radiation through a medium is dependent on the dielectric constant of the medium, as discussed in posts #3, #8.

2. Pulse propagation per the OP is about the movement of

Thus, if you would like to know how long it takes a pulse entering a transmission line to reach its final peak amplitude at the other end you need only know the distributed L,C of the line.

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Thanks for clarifying this, it was very confusing

1. Velocity factor, the speed of electromagnetic radiation through a medium is dependent on the dielectric constant of the medium, as discussed in posts #3, #8.

2. Pulse propagation per the OP is about the movement ofcharge; that depends on the circuit characteristics distributed over the transmission line, namely inductance and capacitance, as discussed in the rest of the posts.

Thus, if you would like to know how long it takes a pulse entering a transmission line to reach its final peak amplitude at the other end you need only know the distributed L,C of the line.

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