[Lowfer] Cat 5 cable

[Jay Rusgrove]

John

And the fact that coax is not a particularly good performer at low frequencies
may explain why adding a preamplifier out at the antenna yields an improved s/n
ratio even though without the preamplifier there is still sufficient noise to
overide the receiver noise floor. I ran into this with my 100' shielded loop
this winter.

Were you using an antenna mounted preamplifier when you noticed the improvement
switching from coax to balanced line?

Jay



John Andrews wrote:

> 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.
>
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