# Inductance at high frequency

Discussion in 'General Electronics' started by Jian, Nov 11, 2003.

1. ### JianGuest

A system (straight wires here):

------------------ L

------------------ L

Self-inductance of each is L (when alone),
mutual inductance is M at low frequency.

How do I obtain L(f) and M(f) from L and M for
high frequency range, say, 100MHz?

Thanks.

2. ### Robert BaerGuest

What is the diameter of the wires?
What is the spacing between the wires?
How far away are they from a ground plane or ground planes?
How long are they?

In short, you must also consider capacitance, and other
transmission-line effects.

3. ### JianGuest

What is the diameter of the wires?
I know what you say. What I'm looking for is a good procedure
to calculate the L(f) based on L and M (there are formula for
straight wire, etc...). So, let's assume:

distance: d
length: l
from ground: g
they are all in a couple of cm range.

4. ### Robert BaerGuest

According to the Allied/Radio Shack Electronics Data Handbook
(1970,1983), a parallel conductor line (ie: twin-lead) impedance is:

Z0 = (276/sqroot(k)) * log(2D/d) where the dielectric coefficent of
the surroundings is k, the wire diameter is d, and the seperation is D.

That is all i can find so far.

As a matter of note, if one makes a "gimmick" by twisting two wires
together, one gets roughly one pF per inch.
Obviously, the actual value will vary according to the insulation type
and thickness, along with the wire size.
Adding a ground plane will slightly decrease inter-wire capacitance if
it is realatively close.

5. ### GPGGuest

And the dielectric of the insulation. Basically unanswerable, unless you elaborate.  