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Re: LF: Re: ADSL EMC with LF receiving?

To: [email protected]
Subject: Re: LF: Re: ADSL EMC with LF receiving?
From: "James Moritz" <[email protected]>
Date: Fri, 06 Dec 2002 12:23:30 +0000
In-reply-to: <[email protected]>
Reply-to: [email protected]
Sender: <[email protected]>
Dear LF Group,

My colleague Dave Lauder, G0SNO, has spent some time investigating ADSL and similar, and has occasionally discussed this in his EMC column in RadCom. Apparently, the idea is that so long as the phone line is accurately balanced, the differential-mode ADSL signal will generate minimal radiated QRM. However, unbalance in the phone line or its termination will lead to "mode conversion" producing common mode signals which can be radiated. This is not too much of a problem for the phone line itself, basically a twisted pair, but once it gets into the house, the UK phone extension wiring uses a 3 wire system which is inherently unbalanced. A splitter which separates out the ADSL and phone signals where the phone line comes into the building ought to minimise this, so the major concern is "splitterless" ADSL, which may be the same as the "wires only" installation that was talked about.

I expect that, like most EMC issues, how much of a problem it actually is will depend on the individual phone installation, how close it is to the LF antenna, and the transmission characteristics of that particular phone line to the exchange etc. I guess it would be mostly a near field source of QRM rather than actually radiating - but with overhead phone lines, "near field" could cover a wide area - probably your neighbor's ADSL would be more of a concern then - you can't just unplug it!

Cheers, Jim Moritz
73 de M0BMU




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