                             Modem Line Noise Solution?

    Please read this entire message and see if you understand it before you
    begin.

    OK, what you' ll need from Radio Shack:

    1 #279-374 Modular line cord if you don't already have one. You won't need
    one if your phone has a modular plug in its base. $4.95

    1 #279-420 Modular surface mount jack (4 or 6 conductor) $4.49

    1 #271-1720 Potentiometer. This is a 5k audio taper variable resistor. $1.09

    1 #272-1055 Capacitor. Any non-polarized 1.0 to 1.5 uf cap should do. Paper,
    Mylar, or metal film caps should be used, although #272-996 may work as
    well.  (272-996 is a non-polarized electrolytic cap) $.79

    1 100 ohm resistor - quarter or half watt. $.19

    1 #279-357 Y-type or duplex modular connector. Don't buy this until you've
    read the section on connecting the Noise Killer below. (A, B,or C) $4.95

    First off, open the modular block. You normally just pry them open with a
    screwdriver. Inside you'll find up to 6 wires. Very carefully cut out all
    but the green and red wires. The ones you'll be removing should be black,
    yellow, white, and blue. These wires won't be needed and may be in the way.
    So cut them as close to where they enter the plug as possible. The other end
    of these wires have a spade lug connector that is screwed into the plastic.
    Unscrew and remove that end of the wires as well. Now, you should have two
    wires left. Green and red. Solder one end of the capacitor to the green
    wire. Solder the other end of the capacitor to the center lug of the
    potentiometer (there are three lugs on this critter). Solder one end of the
    resistor to the red wire. You may want to shorten the leads of the resistor
    first. Solder the other end of the resistor to either one of the remaining
    outside lugs of the potentiometer. Doesn't matter which. Now to wrap it up,
    make a hole in the lid of the mod block to stick the shaft of the
    potentiometer through. Don't make this hole dead center as the other parts
    may not fit into the body of the mod block if you do. See how things will
    fit in order to find where the hole will go. 
    

       ______________                 100 ohm 1/2W
       | Phone Jack |- Red __________/\  /\  ______/\  /\   /  5K Pot
       | In         |                  \/  \/        \/  \/      
       | Parallel   |- Blk ----- N/C                  /|\ (to Center Term. 
       | With       |                                  |         of Pot.) 
       | Modem      |- Yel ----- N/C    1.0 mf (200V)  |
       | Jack       |                   ____||____     |     
       |            |- Grn ____________/    ||    \____|
       |____________|                  \_______||_/
        |         |                            ||
        |To Modem |                      1.0 mf (200V)
        |  Jack   |
        |         |


    Well, now that you've got it built you'll need to test it. First twist 
    the shaft on the potentiometer until it stops. You won't know which way 
    to turn it until later.  It doesn't  matter which way now. You also need 
    to determine where to plug the Noise Killer onto the telephone line. 
    It can be done by one of several ways:

    A. If your modem has two modular plugs in back, connect the Noise Killer
    into one of them using a line cord. (a line cord is a straight cord that
    connects a phone to the wall outlet. Usually silver in color).

    B. If your phone is modular, you can unplug the cord from the back of it
    after you're on-line and plug the cord into the Noise Killer.

    C. You may have to buy a Y-type modular adaptor. Plug the adaptor into a
    wall outlet, plug the modem into one side and the Noise Killer into the
    other. Call a BBS that has known noise problems. After you've connected and
    garbage begins to appear, plug the Noise Killer into the phone line as
    described above. If you have turned the shaft on the potentiometer the wrong
    way you'll find out now.  You may get a lot of garbage or even disconnected.
    If this happens, turn the shaft the other way until it stops and try again.
    If you don't notice much difference when you plug the Noise Killer in, that
    may be a good sign. Type in a few commands and look for garbage characters
    on the screen. If there still is, turn the shaft slowly until most of it is
    gone. If nothing seems to happen at all, turn the shaft slowly from one side
    to the other. You should get plenty of garbage or disconnected at some
    point. If you don't, reread this message to make sure you've connected it
    right.

    1) The pot need not be either 5K or audio taper. I used a 10K 15 turn trim
       pot.  Suggest you use what is handy.
    2) I used 2MFD's of capacitance (two 1MFD's in parallel) Two R.S. p/n 272-
       1055 work fine. Remember that about 90 Volts will appear across red &
       green at ring, so the caps should be rated at 100VDC+.
    3) I ended up with a final series resistance value (100 ohm + pot) of 2.75K.
       I speculate that one could probably use 2MFD and a fixed 2.7K resistor
       and do the job 90% of the time. The adjustment of the pot is not very
       critical.  Changes of +/- 1K made little difference in the performance of
       the circuit.

    This should help some.  I did not originate this file, but I did clarify
    the circuit diagram a bit.  I can't recall where I got it from or I would
    give the author credit, my aplologies to the author.

    I did build this device and it worked for me.  I would also recommend 
    that you check the phone wiring where it enters your building (if
    possible).  You may find the wires are corroded, and that can be a major 
    source of noise.

    Good Luck,
                 Steve Ellis 

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