🚀 go-pugleaf

In article <1992Oct8.120225.6247@fys.ruu.nl> vreeburg@fys.ruu.nl 
(Jurriaan Vreeburg) writes:
>After reading Gary's answer I had some doubt of its correctness. It implies
>that by putting two 50 Ohm coax cables in series, one is able to create a 
>100 Ohm coax cable, which is certainly not true.
>
>I think that putting two cables in parallel doesn't change the impedance, since
>the impedance is defined as:
>
>                   L
>Z = square_root ( --- )
>                   C
>L: inductance per unit length
>C: capacitance per unit length
>
>What happens if we put two cables in parallel: both the inductance and the 
>capacitance
>increase by a factor of two -> Z doesn't change!!! Putting two cables in 
>series doesn't
>change the impedance as well, since L & C are defined per unit length, which 
>don't
>change at all in that case.

Connecting two 50 ohm cables in parallel does half the characteristic
impedance as seen from the input and output.  The inductance per unit length
is half of what it was for a single cable is and the capacitance per unit 
length is twice that of a single cable.  The net change in characteristic
impedance is defined by your formula, one half of that of the single cable.

Remember that the inductance of the wires is a series term, thus two wires in
parallel will decrease the inductance.  The capacitance of the cable is a
shunt capacitance, thus two cables in parallel will increase the capacitance.


						Barry
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|  ___  ________  |       Dr. Barry L. Ornitz          WA4VZQ
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