Quote Originally Posted by jneutron
Hi Tony

The dielectric constant of materials varies with frequency...not vacuum's.

I couldn't find the book from which I got that quote. However, from Becker:[Electromagnetic fields and Interactions]age 260: "both damping and wave velocity will depend upon the frequency, producing a distortion of the signals (of speech, for example) being carried on the conductor."

For zero distortion, (alpha)/omega = sqr(LC)

alpha being the real component of the propagation constant:

gamma=alpha minus j (square root of -1) times Beta.

What it means, is given a real resistance, capacitance, and inductance of the wire pair, there is a sweet spot where no long line distortion occurs.

Unfortunately, that is selected at one frequency (w=5000exp s-1). Dielectrics with frequency varying coefficients will cause the sweet spot to be different for different frequencies, actually eliminating the "sweet spot"

If you peruse JR's site, he mentions the dielectric frequency dependence, and may even link to the belden site where it is stated..


Dielectric constant directly affects capacitance...double one, other follows..so if the dielectric value changes with frequency, the characteristic impedance of the line changes...following Z=sqr(L/C).

Cheers, John
How do you explain the phenomenon that when all telephone calls were transmitted over wire and through repeater amplifiers, prior to microwaves, satellites, fiber optics, a coast to coast telephone call would travel through thousands of miles of wire and if there were this distortion to any significant degree, the signal at the receiving end would have been completely unintelligable but it wasn't? What is the typical degree of distortion and how does that relate to the threshhold of hearing? Is this just another example of finding a theoretical problem and blowing it far out of proportion to anything applicable to audio systems?