[TowerTalk] Re: RFI filter for DSL line?

[dick@pobox.com]

25 NOV, 2000 - 1030 CST

I have had a DSL connection for over 11 months and I have no known RFI
problem on the line.  However, both my 100 Base T computer network and
the analog phone lines in my house use shielded CAT 5 cable.  It was not
cheap or easy to make the changeover last December, but I'm glad I spent
the money.  Anyone building a new home, or remodeling (opening up the
walls), can specify this type of cable and the installation labor should
be about the same as the typical unshielded twisted pair wiring.

As for RFI filtering of a DSL line, the typical analog telephone line
filter will not work because it will also block the higher frequency
DSL signal.  DSL operates well above the analog voice frequency at 2 to
3 Mhz.  Therefore, a filter would have to be designed to pass everything
below this band and this would probably allow some ham band-generated RFI
to ride the DSL line.  Of course, this might not be a big problem if
one were to only operate 20 meters and higher at very low power levels.

There may be some (expensive?) electronic notch-type filter on the market
that would protect a DSL line.  If there is, I would like to know about it
just in case I develop a problem later on.  But the cheap analog voice
line filters now available will block both the RFI and the DSL signal.

- Dick Isely, W9GIG


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