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Written by Bill Noel

Your system has noise!! Ever heard that from one of your users? Of course you have. And did you have a problem? Most likely not. If you had a noisy line then all of your calls would have been noisy. Then where is the problem? It is in what is known as the trunking network. The Trunking Network is a series of lines and trunks that connect switching offices. All offices do not have direct trunks, so they are routed through a connection office. Sometimes these trunks operate on copper cable, sometimes onT-Carrier, and sometimes on the Fiber Optic cables that are currently being installed. Any one of these methods can cause data problems. In fact, any carrier system can cause one way data errors. That is, the BBS can be seeing errors and the user does not see them, or vice versa. The latter problem makes your user know for sure that your BBS is in trouble.

Trunking Network problems are the most difficult problems to solve. Southern Bell does not train their Repair Clerks to handle trunking complaints. What you should do when you experience data problems to a certain exchange is listen to a quiet line into that office. Try to describe the problem in terms of steady noise, "popping," "frying," "other people on the line", etc. Tell the repair clerk that you always have this type of problem when calling the 457 exchange when calling from the 999 exchange. Tell her this is a trunking problem and to please really the report to Trunking Maintenance. Never tell her that you have a data problem. Southern Bell does not guarantee data transmission on non-conditioned lines. (However, a non-conditioned line that meets all of their normal residential service requirements will support data up to 2400 baud with very little problems). Remember that when you buy a cheap modem, you get a cheap modem. Why was it cheap? Because they left things out like noise filters! Keep that in mind when you buy.

But what if you are really having trouble on you line? Be careful before calling Ma Bell with a complaint. If you are not paying them the $1.00 service charge for House Wire Maintenance, they will hit you with about $35.00 per hour to fix the problem, or even if they don't fix it but prove it was you fault. The mini-jacks located in your house can cause you a lot of noise problems. They get all kind of things in them like smoke, grease, animal hair, and dust. These things cause the contacts to corrode. Corrosion causes noise. If you have an OHM meter and the technical skill to use it, lift the house wire from the terminals and check for high resistance shorts in you house with all of your modems and phones removed from the jacks.

Noise problems can also come from the carbon blocks located in the small grey box located where the phone lines enter your house. Normally this condition will appear after an electrical storm or high winds when there may have been currents flowing on the phone lines. These devices belong to the phone company and you should not mess with them. I hope this will shed some light on the subject of noise for you.

Listing NOISE_1.TXT

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.


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.


To: All From: Tom Cryar, Baltimore, MD

Before you spend any money to get the parts mentioned above (cheap as they are), a quick and dirty test will allow you to determine the likelyhood of success using the resistance-capacitance fix:

(An assumption is made that you have a regular telephone hooked up on the same line that you use for telecommuncating. If not, make sure you have one plugged into the 'phone' jack on your modem, or put a splitter or 'Y' in the line and hook a phone set onto the line.)

With the extension phone "on-hook" (not in use), place a call to your favorite NOISY BBS. You all have one or two in your directory.

Once your modem has established a connection, you will probably see the familiar mixture of text and garbage on the screen. If by some miracle you got a clean line, disconnect and try again. For this test, you want a noisy line!

While the line is generating garbage to your screen, lift the handset from the phone which is on your modem line. You should see an instant reduction in the amount of garbage on your screen.

If this test reduces the noise content on your line, the resistor-capacitor fix should help.

I cannot predict what effect the RC fix will have on your normal phone service. I used to be up on phone line requirements, but much has changed over 15 years.

My personal experience regarding noise confirms that your friendly ("Value on the Line") phone company is highly un-interested in your problem. The phone repairman who called to get details on my reported noise problem told me that the phone company's "only responsibility was to make sure I got a dial tone when I lifted the receiver"! Apparently, successful communications is not a consideration.

The problem I was having may shed some additional light on the various ways for the phone company to generate noise instead of data:

The Network Interface Box (phone co. equipment) for my house is on an outside brick wall which faces east. The drop line to the pole goes into a junction box mounted on the east side of the pole. Since my house is in the city, the junction box and Network Interface Box are both shaded from the direct rays of the sun until about 9:30 to 10:00 a.m.

My noise problem seemed to be temperature, time, season and sky dependent: In the winter, my problem was minimal. In the summer, it was maximal. When the air temperature rose above 80 F, the noise rose accordingly. When the sky was cloudy or overcast, the problem was less than when the sun was out in full force.

In addition to the above, the noise problem was time dependent: My phone line was relatively noise-free until about 10:00 to 10:30 a.m., later if it happened to have been cool overnight.

It doesn't take an Eistein-clone to figure out that something is probably heating up in the Network Interface or pole junction box. Most likely since the junction box is quite old, there is a fair amount of corrosion on the wires and connectors in the junction box. When they heat up, the resistance across the connection goes up. You can still push a voice signal across the corrosion but a data signal just ends up with too many bits fouled up.

When I put the extra load of another phone extension onto the line, the phone

company switching equipment sees a lower impedance at my house and pushes a little more current down the line…often enough to overcome the lousy connectors.

In fact, I have never gotten around to putting an RC fix onto my own modem line although it is one of my future projects.

When my line is too noisy to be cleared up by one additional extension on the line, I connect a second extension on the same line. So far, two extensions plus the modem load have been sufficient to clear up even the noisiest line I encounter.

8/12/88 * end *

… Another G-file from The Corner Pocket [DSS] @3121 [301-583-0609] …

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