🚀 go-pugleaf

In article <1992Oct8.120225.6247@fys.ruu.nl> vreeburg@fys.ruu.nl (Jurriaan Vreeburg) writes:
>In <bvr5pd.14o@wang.com> garyf@wang.com (Gary Field) writes:
>
>>dhina@dxcern.cern.ch (Mourad Dhina) writes:
>
>>>Hello,
>>>i am trying to realize a circuit i found in an electronics magazine.
>>>one of the components it uses is a semi-rigid coax cable of
>>>25 ohms impedance. this is the first time i hear of this (i only
>>>knew 50, 75 and 93 ohms cables, which are standard). anybody
>>>knows where to find this?
>>>Mourad
>
>>Put two pieces of 50 Ohm cable in parallel. It should be exactly the same.
>>Gary
>
>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!!! (more stuff deleted)

Whoa! Be careful. Remember that parallel connection of two inductors of equal
value gives half of the inductance while parallel connection of two capacitors
gives twice the capacitance. The resulting equivalent circuit for the
transmission line has twice the capacitance and HALF the inductance and the
parallel connection of two identical transmission lines does indeed give half 
of the original characteristic impedance.
Dave