[RFI] DSL modem problem

Jon Ogden Jon Ogden <jono@enteract.com>
Fri, 05 Jan 2001 17:02:50 -0600

on 1/5/01 11:04 AM, Hare,Ed, W1RFI at w1rfi@arrl.org wrote:

> Radio Shack is now selling a filter designed for high-speed modem/DSL
> filtering.  You can also try their "telephone RFI" filter; I have measured
> them and found that they offer about 30 dB of common-mode rejection without
> significantly attenuating differential-mode HF signals inside the phone
> wiring.

Be CAREFUL!  That DSL filter is NOT for the DSL modem.  I almost bought one
today.  It is for your analog devices on those systems that share analog and
DSL over the same twisted pair.  The packaging specifically says the filter
is NOT for DSL modems.  It even shows a picture of a modem with a circle and
red line thru it.

If I am correct, the analog works by being multiplexed on to the pair with
the DSL service, but they run at different baseband frequencies.  These
filters probably limit the audio baseband so as to not affect the DSL



Jon Ogden
NA9D (ex: KE9NA)



"A life lived in fear is a life half lived."

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