Phil Allison wrote:

"Andy Cowley" wrote in message
...
doug wrote:

Mogami makes coaxial that is very good
Studios use it all the time.

For video. It's no good, it's 75 ohm, you'd need
4 ohm or 8 ohm for speakers. Anyway it seem to cost
a dollar an inch.

;-)

** It is not possible to make a 8 ohm co-ax cable.

But it *is* possible to make an interwoven cable with lots of
insulated strands have a characteristic of 8 ohms.

Such cable was sold as "Tocord" and by Mogami too IIRC.

........... Phil

Did ya notice the smileys? Irony is lost on you? Litzendracht
wire (q.v) is what you are describing. Oh, and it is possible to make
8 ohm coax although I can't conceive of a reason for doing so.

Assuming an air dielectric (relative permittivity, Er ~= 1) and a 1 mm
diameter inner conductor, the inside diameter of the outer conductor
would need to be 1.14 mm. If we consider a more realistic polythene
or ETFE (cousin to PTFE) dielectric (Er ~= 2.6) then the dimension
would be 1.24 mm. - not impossible at all. In fact if you wound some
copper tape over RG213 and used the outer and your tape, with the
original jacket as the dielectric, you'd probably be pretty close.

The characteristic impedance of coaxial conductors, Z0, is given by
Z0 = (138/(sqrt Er)) * log (R/r) . R is inner dia. of outer, r is
diameter of inner, conductors.

Making coax with Z0 ~100 is difficult, though.

best

Andy, M1EBV