[RFI] Ethernet RFI

Martin AA6E msembx-aa6e at yahoo.com
Mon Jan 24 11:26:33 EST 2005


I had lots of trouble with DSL at first -- not with ham RF, but with
getting DSL up and running reliably.  It turned out the problem was
coupling from the AC line, where I had some large lamp dimmers, INTO
the phone circuit.  Funny, I always had dropouts when the sun went
down.  Since replacing the noisy dimmers, I've had few problems.  (Of
course, the phone company didn't lift a finger to help.  I don't know
what a non-tech user would have done.)

DSL modulation, as I understand it, is concentrated below about 1 or
1.5 MHz, so the chances of direct interference with (or from) ham
operations is limited.  Of course, coupling lots of RF into the phone
line is not a Good Idea.  I expect any QRO problems could be cured by
the usual ferrite methods.

I've had no ham interactions with DSL or DSL modems at all with 100
watts of HF.  Now, when we talk about 100baseT and Linksys routers,
that's another story.

Running a direct twisted pair (possibly shielded, possibly with ferrite
common mode filtering) from your home entrance to your DSL modem could
possibly improve your DSL connection and forestall RF troubles.  But if
it's not broken, why fix it? 

In the course of my DSL troubleshooting, I did install a DSL isolation
filter at the phone entrance with a direct (but non-twisted) line to
the DSL modem, so I do not rely on little filter dongles on phones
around the house.  That may help with RF and other noise isolation,

73, Martin AA6E

--- sebdesn <sebdesn at ecentral.com> wrote:

> <Bottom line -- there's a lot more to data cabling than meets the
> <eye, and the precision test set really is required.
> <Jim Brown  K9YC
> Jim, as an additional question near to this subject. The incoming
> telco wire
> for a dsl line;
> Is the overal length and make up critical?
>  My line hits the house about three feet from the modem connection.
> However,
> it goes into the attic,then to the basement, and then back to the
> modem area
> probably a total of a 100' of 50 year old wire.Would I gain anything
> by
> getting into the box at the down lead and plugging a blocking filter
> on the
> wiring to the house, and then adding a separate cat 5 run for the ten
> feet
> directly to the modem? Any enlighten would be appreciated!
> Bud  WØHG
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