[TowerTalk] Formula

[Jim Lux]

This is a non trivial calculation, for a variety of reasons.  NBS  Circular
74, published more than 50 years ago, will have some formulae.
The "tome" in this field is a work by Grover... Some of it is summarized at
http://home.san.rr.com/bushnell/self_inductance.htm
You'll also need to know the frequency (skin effect changes the effective
thickness of the copper strip, which changes the inductance, somewhat).

Also, bear in mind that inductance of isolated conductors is kind of a funny
thing, since the conductor has to be part of some loop (otherwise, current
couldn't flow, so there couldn't be di/dt, etc.).  What you'll find is a
series of equations that approximate the inductance of a conductor of a
given dimension at a given height over a reasonably high quality ground
plane, with the unstated assumption that there's an image formed in the
ground plane. Fortunately, the dependence on ground plane height is fairly
weak.

When designing, e.g., circuitboard traces or microstripline, one calculates
the inductance using finite element methods, or use a canned approximation
for "popular" configurations (i.e. 50 ohm lines with 1 oz copper, etc.)

In any case, a working value of 1 microhenry/meter is good for rough design,
for conductors that you can hold in your hand, (i.e. no 8 foot wide sheets,
etc.)


----- Original Message -----
From: "stephen rutherford" <sprutherford.bunny at comcast.net>
To: <towertalk at contesting.com>
Sent: Tuesday, October 21, 2003 11:53 PM
Subject: [TowerTalk] Formula


>     Where is the reference database and formulae available to calculate
the
> lead inductance of copper strapping given the width and depth in inches
and
> the length of the copper strap in feet?
>     The interest is in the broad range, especially when it for lightning
> damage or EMP hazard reduction.
>     Thank you for your assistance with this question.
>
>
> --
> Rutherford Resources
> Stephen Rutherford
> 2230 SW 106th Place
> Portland, OR 97225
> 503-525-7863
> Email; sprutherford.bunny at comcast.net
>
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