[RFI] DSL interference

W0MU Mike Fatchett w0mu at w0mu.com
Thu Feb 19 17:13:54 EST 2009

I have the rfi filter from Excelsios (sp) coming.  Should be here tomorrow.
I will let you know if it helps with my issues on 40m with my dsl modem.

Mike W0MU 

"A slip of the foot you may soon recover, but a slip of the tongue you may
never get over." Ben Franklin
-----Original Message-----
From: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com] On
Behalf Of W2RU - Bud Hippisley
Sent: Thursday, February 19, 2009 8:42 AM
To: rfi at contesting.com
Subject: [RFI] DSL interference

I have had DSL service from Frontier Communications here in the remote wilds
of upstate NY for about five years.  Prior to this summer I had arrived at a
tolerable "truce" between my legal limit 160-meter transmissions and my DSL
link -- a truce which depended primarily on the use of Type 31 ferrites on
all the cables coming into the telco- supplied Siemens Speedstream DSL
modem:  power from the wall-wart, the phone line, and a few ethernet cables.

During that period, my DSL modem was located in the basement of the _older_
part of our house, about 100 feet from my transmitting vertical, which is
about 30 feet from the _new_ end of the house, where my shack is.  At the
time, the telco entrance and network interface device (NID) were at the old
end of the house, just beyond my radial field, but my AC service entrance
was (and still is) on a "new" exterior wall, a few feet from my shack, so I
could have a single point ground (SPG) for everything coming into the house
(except the phone line).

To minimize future lightning damage to home electronics equipment that
necessarily bridges the AC power and the telephone line (cordless telephone
base, fax machine, satellite TV receiver, etc. PC fax/ modem), this summer I
had the telco folks relocate their entrance point so as to put their NID
right next to the AC utility meter, so  
they could attach to the same SPG.   This, of course, means that the  
buried phone line (shielded twisted pairs) is now about 125 feet longer that
it was.  More importantly, it now comes within about 35 feet of my
transmitting vertical, and lays within part of the radial field for that

The telco guy installed a plastic-enclosure whole-house DSL filter
immediately adjacent to the NID, and then ran (perhaps 20 feet of)
unshielded Cat 5E TP up to the room above, where the DSL modem is now
located (next to my shack).

Now no amount of filtering with Type 31 ferrites keeps me from shutting down
the DSL modem on either 160 or 80.  Since my wife works from home much of
the time, and internet connectivity is an important part of her job, this is
an intolerable situation for her.

Over the past two weeks the local telco tech and I have been trying various
things to get my DSL interference rejection back to its previous
"acceptable" level.  Things that have not worked include:

   *  Temporarily disconnecting all "optional" cables (ethernet links) from
the modem
   *  Replacing the unshielded Cat 5E TP from the DSL filter to the modem
with shielded TP, grounded only at the SPG end
   *  Moving the DSL modem to the old end of the house by extending the DSL
wiring (using unshielded Cat5E; we didn't have enough shielded TP on hand)
   *  Filtering the POTS wiring in the house where it comes out of the DSL
filter box
   *  Removing the POTS wiring from the DSL filter box entirely
   *  Disconnecting the lightning arrestors in the NID
   *  Skipping the NID and the DSL filter box completely (i.e., running the
telco service directly into just the DSL modem -- through a ferrite, of
   *  Wrapping the DSL modem in aluminum foil
   *  Swapping out modems
   *  Looping a few turns of the shielded TP entrance cable through a Type
31 ferrite at the entrance to the NID

My telco guy has a background of having installed shielded wiring telephone
systems in government buildings near high-power radar transmitters, so he
has a preference for certain shielding techniques.  Unfortunately, keeping
1.8 MHz RF out of DSL links is not exactly the same problem.  He has been
bouncing my problem off the technical staff back at telco HQ, and they have
pointed out a few things, such as:  it's the same problem they have with AM
broadcast station interference to DSL in civilized areas; and it's
aggravated by the fact that I'm at about the 3.6-mile point on a DSL path
that's only supposed to extend 3.5 miles....:-)

The Speedstream modems are programmed to quit and reboot if the errors
accumulated in a certain period exceed 30 or so.  I've asked the tech to see
if he has any way of reprogramming that number from the central office or
remote switch.  Because of the highly intermittent nature of my
transmissions, that change might reduce the aggravation factor for my

Does anyone have other suggestions, short of giving up my SPG lightning
protection and going back to having the telco service enter the building at
the farthest point from my tower?  Are there, for instance, other DSL modems
out there that have shown themselves to be more bulletproof in actual use?

Bud, W2RU
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