Oh - your capacitance of 10nF/10m is high for standard telephone
cable. It's more in line with PVC insulated "internal" (short
distance) wiring. Telephone twisted pair capacitance varies according
to type of cable but typically varies between about 35nF/km for air
pressurised "dry core" cable up to about 64nF/km for jelly filled
underground types.
RP

On 10/11/05, Richard Prosser <rhprosser@gmail.com> wrote:
> The char impedance of the cable = sqrt(L/C) at high frequencies so if
> you know the impedance then the inductance is easy.
> However. the inductance does increase slightly as frequency increases
> due to skin effect. IIRC its about 5% increase at some frequency
> dependent on the size (& shape) of the conductor.
> Also the impedance at high frequency may not be known. It's likely to
> be ~120ohms or so but does depend on the geometary etc. 600ohms is a
> low frequency value if you see it written anywhere - and is more in
> line with the old overhead wires than with modern twisted pair.
>
> Or you could just use the value of 0.5mH/km as a _very_ approximate value.
>
> RP
>
> On 10/11/05, David Van Horn <dvanhorn@microbrix.com> wrote:
> > > a real test with a simulated line? If the latter you are probably best
> > to
> > > get a reel of cable from the local radio Shark or similar store, and
> > find
> > > the inner end, and connect both ends to your circuit.
> >
> > I've seen it done with lumped constants, but I'm having trouble
> > remembering which book it's in.
> >
> >
> >
> >
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>

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