In message , Bob Myers writes
>> In a 1930s edition of the Bell System Technical Journal were two cross
>> sectional views of co-axial cables with two centre conductors surrounded
>> by a single screening braid enclosing both.
>
>Shielded twinlead, in other words. By definition, this is
>NOT a "coaxial" cable. It's sometimes referred to as a
>"twinaxial" - at least, that's what Belden calls it. Check out
>their types 9250 (95 ohm), 9207 (100 ohm), or 9271 (the
>classic 124 ohm). Such things are used for balanced lines that
>have to be protected from crosstalk, etc..
>
>Bob M.
>
>
You could also mooch around your local computer salvage place and watch out for IBM System 36/38 or AS/400 kit, they used Twinaxial cable, though I'm not sure of the impedance