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Re: [RFI] RFI U-verse

Subject: Re: [RFI] RFI U-verse
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Sun, 27 Feb 2011 13:48:24 -0800
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
On 2/27/2011 12:11 PM, BEATTIE, GORDON (ATTSI) wrote:
> The key thing is to not just reduce off portions of the spectrum through
> the incorrect application of chokes.

One problem with DSL is that the signal on the hard wired phone line 
extends from low audio up to nearly 4 MHz. As I understand it, these 
systems will limit their bandwidth (which lowers the max data rate) if 
they see a loss of bandwidth in the circuit or see noise in the higher 
part of the spectrum.  My advice with respect to differential filtering 
of these circuits is to use a good filter design program to design for 
the widest possible bandwidth that does not include the transmitter 
fundamental, and for a characteristic impedance of 100 ohms.  This IS 
the Zo of CAT5 cable, and most closely spaced pairs are in this range or 
just below it.  There are some decent filter design programs are 
distributed free with the ARRL Handbook, and they are also available for 
free download on the author's website. The one I'm thinking of is called 
Elsie. Jim Tonne is a contributor to the ARRL Handbook.


If the interfering transmitter is on 160M and the coupling is 
differential mode, I would first install the best CAT5/6/7 cable I could 
find for the wired portion of the link and get serious with common mode 
ferrite chokes. If this were not sufficient, I would add the 
differential filter noted above, and, if still more was needed, lower 
the cutoff frequency to about 1.5 MHz. This would reduce the data rate, 
but as I understand it, most DSL systems would continue to work.  Would 
this be a reasonable approach with UVerse?

73, Jim K9YC
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