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Eliminate background noise
NOTICE: TO ALL CONCERNED Certain text files and messages contained on this site deal with activities and devices which would be in violation of various Federal, State, and local laws if actually carried out or constructed. The webmasters of this site do not advocate the breaking of any law. Our text files and message bases are for informational purposes only. We recommend that you contact your local law enforcement officials before undertaking any project based upon any information obtained from this or any other web site. We do not guarantee that any of the information contained on this system is correct, workable, or factual. We are not responsible for, nor do we assume any liability for, damages resulting from the use of any information on this site.
Modem Noise Killer (alpha version)
With this circuit diagram, some basic tools including a
soldering iron, and four or five components from Radio Shack,
you should be able to cut the noise/garbage that appears on
your computer's screen.
I started this project out of frustration at using a US
Robotics 2400 baud modem and getting a fare amount of junk when
connecting at that speed. Knowing that capacitors make good
noise filters, I threw this together.
This is very easy to build, however conditions may be different
due to modem type, amount of line noise, old or new switching
equipment (Bell's equipment), and on and on. So it may not work
as well for you in every case. If it does work, or if you've
managed to tweek it to your computer/modem setup I' d like to
hear from you.
I'd also appreciate any of you electronic wizzards out there
wanting to offer any improvements. Let's make this work for
everyone!
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. 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.
***END OF ORIGNAL FILE***
ADDITION TO ORIGNAL FILE - 2/29/88 - Mike McCauley - CIS 71505,1173
First, a personal recomendation. _THIS WORKS!!!_
I have been plagued with noise at 2400 for some time. I went
round and round with Ma Bell on it, and after they sent out
several "repair persons" who were, to be kind, of limited help
in the matter, I threw in the towel. I saw this file on a board
up east a few days ago, and thought I'd bite.
Threw the gismo together in about 10 minutes, took another five
to adjust the pot for best results on my worst conection, and
guess what? No more worst connecion!
A few pointers:
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.
Hope it works as well for you as it did for me.
Mike McCauley
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2nd ADDITION TO ORIGNAL FILE - 2/6/89 - Rich Appel - Philadelphia, PA.
Visual CIRCUIT DIAGRAM:
??????????????????????????????????????????????????????????????????????????????
? ?
? ?
? DUPLEX JACK ?
? -OR- ==============\=================== MODEM ?
? 2ND WALL JACK \phone cord ?
? ETC. ?
? | ?
? | /phone cord ?
? |========/===================== MODULAR JACK ?
? | | ?
? | | ?
? ============================ RED WIRE | |===== GREEN WIRE ==== ?
? | | ?
? | | ?
? | | ?
? | 1 - 2.7 K OHM VARIABLE RESISTOR NON-polarized | ?
? ===== RESISTOR ======= "POT" ===== Capacitor == ?
? 5-10 K OHM 1-2 Mfd ?
? ?
? ?
??????????????????????????????????????????????????????????????????????????????
3RD ADDITION TO ORIGINAL FILE 1/24/92 Michael Thompson N2NLQ
Voorhees NJ
This circuit appears to be correct.
Another option you may wish to consider, is one of direct installation into
your telephone line. This can be acomplished by finding the wiring block
for your phone line. Once you've located it, you should be able to
determine where the red and green wires connect, and make the apropriate
connections.
This setup is more cost effective than buying plugs and jacks.
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