Re: [IRCA] Cable connectors

[Chuck Hutton <charlesh3@xxxxxxx>]

I agree with Craig - CAT5 has spec values for crosstalk that have to be met from 1 MHZ up to 1 GHZ. At 1 MHZ, I think it is fair to expect at least 40 dB of attenuation.
 
Craig: Shielded cable is the norm in Europe but is not so popular here in the US. Even so, you'll always find some on eBay.
If you're in a testing mood, it would be good to try some CAT6 (better crosstalk specs) and CAT7 (shielded pairs and shielded bundle, with even better crosstalk) if you can find some that is cheap. 
 
Chuck
 

> From: bubba@xxxxxxxxxxxxxxxxxxxx
> To: irca@xxxxxxxxxxxxxxxx
> Date: Mon, 6 Sep 2010 17:59:23 -0400
> Subject: Re: [IRCA] Cable connectors
> 
Rick wrote: 
> > The problem with any balanced feedline is always line-balance. Since the
> > electric and magnetic field of the signals extends outside the physical 
> > area of
> > the twisted pair, there will always be interaction between pairs within a 
> > CAT
> > type cable. You would need far more spacing between pairs than is 
> > available in
> > the CAT cable design to prevent interaction between pairs.

And Craig replied: 
> I might agree with that except CAT5 is designed to limit the interaction. 
> The individual pairs are tightly twisted, but not identical turns per foot 
> for each of them. What that does is cancel the interaction. The four pairs 
> are also twisted inside the outer cover which further limits pickup. In the 
> test, I only used a single pair and the others were floating. I set it to 
> use the Blue-Blue/White pair.
> 
> > laying the cable on the ground or near to conductive surfaces will also 
> > upset
> > the line-balance (for UTP cable.) And this prevents the common-mode 
> > rejection
> > of signals common to both wires of the twisted pair from canceling 
> > completely.
> 
> I haven't found a source for the shielded cable or appropriate RJ-45 
> connectors and the different crimp tool. I have had access to a 25' 
> shielded cable but that again made no difference from the common type.
> 
> Bottom line to me is that the CAT5 is better than coax. I have not done an 
> A-B test with CAT5 and speaker wire. I may get to that.
> 
> One of the more important things I've learned in my lifetime is to leave my 
> ego outside. If someone has an improvement, I'll grab that in a heartbeat. 
> I do thank you for your comments on this.
> 
> Craig Healy
> Providence, RI
 		 	   		  
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