LINE NOISE

Telephone Line noise is critical to your connect speed. Marginal lines will prevent you from obtaining any speeds at, or near 28.8K. Many areas are plagued with corroded telephone wires and antiquated relays & switches.

REMEMBER, higher connect speeds pass data at higher speeds. The faster the data is traveling, the more susceptible it becomes to line noise! Line noise is the AIDS of telecommunications!

To determine the quality of your connections use the AT%Q command. (Refer to your AT command manual to see if your model supports the AT%Q command)

The "NORMAL CONNECTIONS RANGE FROM 0 to 15, AND APPROACHES 60 FOR PROGRESSIVELY POORER CONNECTIONS." Many times this can go as high as 50, 100, and 127. 127 is as high as the modem will measure. That is SERIOUS line noise! Around 50 or above means you are about to be disconnected.

Modems with Rockwell RC96xx, RC144xx and RC288xx chips have a fantastic feature, an E.Q.M.! It will actually measure line noise and allow you to observe it with the E.Q.M. ("Eye Quality Monitor.")

Before you condemn your high speed modem, use the following test when you have connected to a BBS. You may be in for a very rude awakening concerning the poor quality of your telephone lines!

Test Procedure:

  • 1 - CONNECT to another modem. (A BBS at ANY speed is OK for testing.)
  • 2 - TYPE: +++ (You will receive an OK - meaning you are in Command Mode)
  • 3 - TYPE: AT%Q <ENTER> (You will see a number.)
  • 4 - TYPE: A/ (Do A/ repeatedly and quickly about 25 - 30 times.)
  • 5 - Watch the number that keeps appearing after each A/

    The number should be anywhere from 001 to 015. If it says over 30 you have serious line noise. If it gets near 50 you are going to loose the CARRIER DETECT. If it drops to 000 you have lost the CARRIER DETECT.

  • 6 - TYPE: ATO to return to the on-line state and continue with the BBS. That is the letter O not the number 0 (zero.)

    Try this test with a BBS that you usually have no problem connecting with. The AT%Q will probably show readings about 002 to 015. Next call a BBS or two that you usually have problems obtaining high speeds with. You will probably see much readings with the test. I have seen normal readings for 20 or 30 seconds, then it sky roets to 100 or more for a few seconds. This proves your problem is with line noise, not the modem.

THE ULTIMATE MODEM CONNECT SPEED TEST:

There is another way to test your CONNECT modem speed and to completely eliminate the "Is it line noise" question. Bring your computer to the home of another person who has a 28.8K modem. Rather than plugging your modem into a telephone wall jack, plug it directly into his modem jack. There will be no dial tone, but you won't need one. The connect will be instantaneous. There will be NO line noise. There will be no chance of any external interference.

  • 1-Run a terminal program on both computers.
  • 2-On computer type: ATX3DT [ENTER] The X3 disables DIALTONE detect.
  • 3-On the other computer type: ATA [ENTER] This answers.

Note: This will start the connection negotiation.

If you still have a problem connecting at 26.4K and 28.8K then you can blame it on the modems, but not until you do this direct modem to modem test.

In short, STOP blaming your modem until you understand how to set it up, how to control it, and you have run these tests. If line noise is your problem, then go after your local telephone company. You should also be aware that your telephone company will probably tell you that they do not guarantee noise free telecommunications lines, they just guarantee good quality voice lines.

BUYING A NOISE FILTER

AT&T sells a telephone line filter. The model number is Z100A. Call your local AT&T Phone Center for the price. Buy it and try it. If it doesn't help, return it and get a refund!