> In my son's case however, the filter drops
his download speed from around 30kb to 8kb.
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.
73,
Ed Hare, W1RFI
ARRL Laboratory Supervisor
225 Main St
Newington, CT 06111
Tel: 860-594-0318
FAX: 860-594-0259
Internet: w1rfi@arrl.org
ARRL Web: http://www.arrl.org
ARRL Technical Information Service: http://www.arrl.org/tis/
-----Original Message-----
From: Michael D. Brown [mailto:mdbrown@iquest.net]
Sent: Wednesday, November 15, 2000 12:17 AM
To: rfi@contesting.com
Subject: Re: [RFI] DSL modem problem
Thanks for the replys Ernie and John.
I am evidently coming in via the phone line itself.
I am actually getting into two DSL modems, my
own, and my son's next door. We have tried
the plug in filters availabe from the phone
company, and they do work at stopping the
RFI. In my son's case however, the filter drops
his download speed from around 30kb to 8kb.
I have the lower speed account, and I can't
get any data to pass once a filter is put in
place here at my house.
I'm getting into both modems running 100 watts
on 80-10 meters. I don't have an antenna up
for 160 right now. I'm using a TH3 and inv
vees for 40 and 80. The tower is 40ft, so the
beam is at 40ft, and the inv vees just below
that.
I've tried ferrites on the cable from the jack to
the modem. No luck there. One thing I can
try I guess would be to put more ferrites on
my son's modem. This is really more of a
problem of me bothering his then it is my own.
If I'm on the hf rig, then I'm not on the internet
anyway at that moment.
We probably don't have the best phone lines
in this neighborhood. Most of the houses were
built in the early 60's.
Thanks... 73
Mike
----- Original Message -----
From: "John Kaufmann" <john_w1fv@telocity.com>
To: "Michael D. Brown" <mdbrown@iquest.net>; <rfi@contesting.com>
Sent: Tuesday, November 14, 2000 22:28 PM
Subject: Re: [RFI] DSL modem problem
> At 09:58 PM 11/14/00 -0500, Michael D. Brown wrote:
>
> >Has anyone had any luck in solving a problem
> >of an hf transmitter getting into their DSL modem?
> >I emailed the manufacture of the modem, but
> >got no response. Response from my ISP was
> >that DSL modems were indeed very sensitive
> >to rf, and that they didn't know of any fix.
> >
> >Thanks...
> >
> >Mike K9MI
>
>
> Is there a specific frequency band that causes problems with
the
> modem? DSL systems, depending on the speed, use lower portions
of the HF
> spectrum (in telephone lines, of course, and not over the air)
that could
> be susceptible to interference from the lower HF bands,
particularly 160
> meters. Supposedly the spectrum of DSL signals is notched so
that it
> doesn't radiate on the amateur bands, since it was recognized
by DSL
> engineers that even small leakage could cause interference to
amateur
> radio. Indeed my DSL modem doesn't appear to produce any
discernable RFI
> in my receiver on 160 meters. However, this does not mean that
the modem
> won't be susceptible to external interference, just like any
other
> electronic device. If the modem is an external unit, try the
same fixes
> you would use for other RFI problems, like power line filters
and chokes or
> ferrite beads (you may need a lot for low frequencies) on the
telephone
> line and the line from the modem to your PC.
>
> 73, John W1FV
>
>
>
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