Modem Line Noise

When To Suspect Line Noise

  1. You see garbage on the screen of your terminal emulation program (like Telix or ZTerm).
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  2. You get disconnected for no reason apparent to you (like someone else in the house picking up the telephone).

How To Check Line Noise

In your terminal program (like Telix or ZTerm), type
+++
quickly. This sequence occuring close together in time is a signal to your modem to wait for an ATtention code from you rather than continuing to send your data to the remote modem. After a pause, you will be able to type AT co mmands to your modem. To check the line noise, type
AT%Q
You should repeat the AT%Q command several times to get an average result. The result will be a number between 000 and 255 where 000 is the best possible line condition. Numbers like 020 o r higher indicate rather high line noise. A lower connection speed will be more reliable.

To return to your terminal program, type
ATO
to go back Online. You will want to delete the +++ sequence before continuing. However, if you decide to Hangup, the command is
ATH

More Information on Line Noise

Go to Supra Corporation to the File Library to General Information on telephone lines at ftp://ftp.supra.com/pub/gen_info/tel_line.txt

More Information on AT Commands

Supra Corporation keeps a list of AT commands for their modems at ftp://ftp.supra.com/pub/gen_info/at_lis t.txt. Most of these AT commands should be Hayes compatible and work on most modems.

Created: July 2, 1996
Last Revised: July 2, 1996 by jj