The best choice for any circuit used for connecting a computer to the telco's trunk (Inside Wiring, or Subscriber's Side of the NID) is something in the twisted pairs catagories - or use shielded cables.
This would include wiring for ADSL (common type or "flavor" of Residential Digital Subscriber Line), and Analog MODEMs.
This way, you can (try to) eliminate as much RFI / EMI from falling into the phone line circuit as possible, reduce the coupled effects of two separate phone lines in one cable, plus keep the line tuned and set at a somewhat steady value.
UTP (Unshielded Twisted Pair) cable is most convenient and requires simpler installation tasks. Common types include CAT 3 UTP and CAT 5 UTP Multi Pair Cable.
STP (Shielded Twisted Pair) is more expensive and requires more work to install.
IBM's "Type 1" is an example of STP Cable.
I won't even get into Shielded Untwisted Pair cables!
Now for a few "...,But" examples!
I have seen a couple successful ADSL setups, where the "older" 4 Conductor "JK" type cable was used between the NID and the Brouter (Bridge Router - Proper name for what has become an Oxy-Moron slang term "DSL MODEM").
Having only seen about 30 minutes of Browsing time across these connections, they did manage well (don't know if the throughput died after I left, or not!).
The most significant reasons why these setups were successful are:
* Short Distance From NID To DSE (Brouter),
* No Analog Devices Coupled To The Line (via the filters normally included with DSL packages - used to connect stuff like fax machines and regular telephone sets to the circuit with the DSL connection),
* No Visible Signs Of HAM Radio Operators In Immediate Area / No Sign Of "Big or Small Yagi's" in neighbor's yards (didn't see any large HF / VHF / UHF Antennas masted atop towers),
* Relatively Decent Electrical Appliances And Circuitry.
A few things to consider would be:
- What type of interference is falling onto the telephone line circuit,
- How intense the noise is,
- What Analog stuff is connected to the DSL circuit,
and probably the most important;
- Does the noise come in on the Telco's Trunk, meaning does the noise originate on the telco side of the NID.
As mentioned before, try relocating the DSE closer to the NID, then see what the results are.
Check around for crappy connections on anything possible (POTS circuits and AC Power circuits).
Also remember that each Passive device connected to the POTS circuit will affect the signal's power - and can bring in noise (or even create noise) if not correctly designed or connected.
I'll add more later if you like - and if you can add a little more info, that would be cool!
p.s. edited to fix spell-eeng again!
[This message has been edited by Scott35 (edited 01-28-2003).]