When To Suspect Line
Noise
With data calls, line noise can cause numerous problems. In
general, the faster you communicate, the better your phone lines need to
be. When you get up to 28.8 and 33.6 bps, it is critical that you have
clear lines from end to end. Line noise can cause the following problems
when trying to make high speed data connections:
- No connection.
- Connection, but only "garbage"
characters appear on screen.
- Connection, but no communication.
- Connection, then disconnection for no apparent
reason.
- Connection, but modem speed drops.
How To Check Line NoiseConnect to a remote computer or BBS
using a terminal emulation program such as Telix, ZTerm, or Hyper
Terminal.
Type: +++ (OK, should appear on your screen)
Type:
AT%Q (press enter) (You see a number on your screen ranging
from 000 and 255)
Type: A/ (a few times, repeatedly) (You see
numbers each time you press the enter key)
Type: ATO (the letter O) to
return from the command mode
Any numbers over 30, you have
considerable line noise.
* Note: The above modem commands are not
supported by all modem manufacturers.
Where Does the Problem Originate?Line noise can be introduced
at the remote site, by the phone lines, or at your local site. Before
making any changes, try calling a few different remote modems, to see if
you have the same line noise problems in each instance.
One of the
more common and familiar introduction points of line noise is in the
telephone company's system and even here there are several ways noise is
introduced. A signal is routed through multiple stations before it
eventually makes it to the other end and some of these stations aren't
exactly new. Older areas may have older, less sophisticated equipment that
is more apt to be affected by ambient noise. This is one reason some
people continue to have noise problems even after hanging up and calling
back multiple times. Your local telephone company is required by the FCC
to provide a minimum level of quality on the lines it maintains for your
use. Contact your local telephone company and ask them to perform a line
qualification test if you suspect this may be the problem.
Another
common noise introduction point is in your home. Most residential homes
have televisions, radios, microwave ovens, VCR's, and if you are reading
this, a micro-computer. All these devices radiate radio waves that can
(and often do) get into the phone lines and cause noise. Electric motors
and mechanical dimmer controls can introduce noise into the electrical
wiring in your house and cause problems. If your line noise problem does
not go away after repeated hanging up and calling back, then you may be
suffering from one of these household problems. If you are suffering from
this problem, you can take steps to eliminate it. First of all, turn off
EVERYTHING except the fridge and see if the noise persists. If it goes
away, then start turning things back on, checking the computer each time
until you see the noise start up again. It may be that a single device is
not bugging you but several devices plotting together to annoy you. This
elimination tournament may take awhile.
