[Lowfer] Cat 5 cable

[John Andrews]

Bob,

> I still dont understand how an unshielded ,twisted pair can provide
> better isolation than a piece of coax.
> but remember the frequencies involver are relatively low. The important
> factor appears to be isolation
> and a balanced twisted pair will do a better job than a shielded un
> balanced coax
> We find that in general a balanced loop works better than one that is non
> balanced. The problem isnt loss as much as its isolation and balance

I think you are exactly right. The broadcast and professional audio guys
have been finding that the miles of shielded paired audio cable they have
traditionally used can be replaced by unshielded Cat  3 or 5. This is
assuming that the source and any loads are balanced. The shielding has
little effect on noise coupled via magnetic fields.

My "ideal" receiving loop transmission line is Canare "Star Quad" microphone
cable, which has four highly twisted wires and an overall braided shield.
There are two white wires and two blue wires. The pair is formed by using
both whites and both blues at each end. Characteristic impedance is quoted
as 45 ohms, meaning that it fits well into a nominal 50 ohm system. The
braided shield is much better than foil in outdoor applications where the
cable may be flexed. With both ends of the cable connected to transformers
and the shield grounded at one end only, you should have the best possible
noise performance. I've tried this up in Maine, and it is quieter than using
RG58 with transformers. Have to order some of the cable for home.

John A.