[3moons]

I have questions on a type of cable found in my workbench junk box. On the surface it looks like a typical microphone cable found anywhere. There are two center leads. One with red insulation. One with clear. Each of these colors is then covered with black insulation. Then there are copper spiral strands as the shield. It is a very flexible cable. Nothing too surprising except when examined closely. I used a 10 power loupe. The copper strands of the center leads AND the copper strands of the shield are both really spiral strands of copper wrapped around centers of an insulated material. I've seen a design similar many years ago in a Telco cable. This one is a discontinued cable sold under Radio Shack's Archer brand. Can anyone explain the design? Why of the design? And where I might find something similar to experiment with? Thanks. jim...

[Ulas]

I am not a cable design expert but I think I can provide a reasonable answer to some of your questions.

Spiraling wire strands around an insulator core is common practice in litz-wire construction. It is done to reduce skin effect at radio frequencies by maximizing the number of strands that are at or very near the outside “skin” of the cable. Whether or not skin effect is a significant factor at audio frequencies is arguable, to say the least.

The construction you described is also common in microphone and other cables that are handled a lot. It increases the strength, flexibility, and heft of the cable. If the relatively small diameter conductors were twisted and insulated in a more conventional way, the cable would be skinny, stiff, likely to kink, and would be difficult to handle and coil.