[RFI] DSL interference

W2RU - Bud Hippisley W2RU at frontiernet.net
Thu Feb 19 10:42:29 EST 2009

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 antenna.

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 course)
   *  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 family.

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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