[Ham-Computers] interference to dsl modem

[Jerry K]

Bill, how close is the DSL modem to your transmitter? If it's anywhere
close, the first thing I'd do is relocate the modem to a phone jack in
another part of the house and run a shielded Cat 5 drop back to the ham
shack PC. It's easy to jury-rig a loooonnng Cat 5 drop and string it out the
door of the ham shack to see if this works before committing to running a
permanent drop.

If that doesn't do it you might try a homebrew low pass filter that cuts off
just above the broadcast band (instead of 30 mHz as most do). The DSL signal
runs in approximately the same band as broadcast radio. Unfortunately, most
of the standard telephone line RFI filters sold won't work with DSL because
they are built to combat local BC station interference and their upper
cutoff freq is too low. There might be one out there by now that works (I
retired a year ago so don't follow all the latest gadgets) but all the ones
I tried on the job wouldn't fly. They filtered the problem out all right,
along with the DSL signal. Ha.

You might have to also combine the filtering with shielded Cat 5 instead of
what Ma Bell provides. Be careful if you try adding physical shielding to
the modem itself, most DSL modems are already running near their convective
heat dissipation limit by design, so it's not hard to fry one if you tin
foil it. I think Ma Bell has gone 100% 2Wire in my area, but the older
Efficient Systems and Alcatel modems also run hot, as do Ma Bell's older DSL
routers.


As for the cordless phone, in about 8,000 DSL installs and repair calls for
Ma Bell, I ran into only a couple of cases where this problem popped up. In
both cases the cordless base unit was the older 800 MHz type, and in both
cases the base unit was sitting next to the modem. Moving the base unit to
another part of the house solved the problem. But if it persists and it's an
800 MHz unit, you might have to upgrade to a 2.4 or 5 GHz unit.

Good luck.

Jerry W5KP, Ma Bell Retired


-----Original Message-----
From: ham-computers-bounces at mailman.qth.net
[mailto:ham-computers-bounces at mailman.qth.net]On Behalf Of bill barr
Sent: Monday, January 31, 2005 6:41 AM
To: ham-computers at mailman.qth.net
Subject: [Ham-Computers] interference to dsl modem


What steps have some of you all taken to minimize interference to these
cheap modems that the dsl companies give you....mine even bugs out with a
little cordless phone...50 watt cw signal on any band will take it out.It
has no problem resynching afterward though.
thanks
bill


bill barr
n4uaj at earthlink.net




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