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Old March 17th 06, 01:43 AM posted to rec.radio.amateur.antenna
Roy Lewallen
 
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Default Coils are transmission lines

Reg Edwards wrote:
Reg, would you care to share your formula for velocity factor?

==========================================

Cec, can't you find it in your bibles?

Velocity = 1 / Sqrt( L * C) metres per second

where L and C are henrys and farads per metre.

What you really want to know is how to calculate L and C from coil
dimensions. But you won't find that from any bible.


. . .


What seems to be getting lost in the discussion is that L is *series* L
per meter and C is *shunt* C per meter -- that is, the C to another
conductor(*). C is not the self-capacitance of the inductor.

(*) Conductors also have capacitance to free space, but I'm not at all
sure the transmission line equations for such things as velocity are
valid if this is used for C. The equation for the resonant length of a
wire in space is very complex and can't be solved in closed form, and
even approximate formulas are much more complex than those for
transmission lines. So while transmission lines and antennas -- or
radiating inductors -- share some characteristics, you can't blindly
apply the equations for one to the other and expect valid results.

Roy Lewallen, W7EL
 
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