Copyright ©1998- 2001 by Randy B. Singer. All Rights Reserved. For personal use only. This work may not be: reproduced in any form, mechanically, electronically, or photographically; quoted; Xeroxed; abstracted; condensed; or disseminated in any way without the author’s express written permission.

Back when the first V.32bis (14,400 bps) modems appeared, many users had trouble connecting to online services with their new high-speed modems due to noise on their phone lines. I could help many people with line noise problems by either tailoring the initialization string for their modem, or by instructing them on how to get the phone company to repair and clean up their phone lines. For the few people for which neither of those options worked, I recommended line noise filters.

There are a few companies that advertise in magazines that sell these filters for as much as $150. I started experimenting with homemade filters to see if I could build one just as good for less money. After a lot of experimentation with components of different ratings, I hit upon a setup that solves the problem almost every single time. The line noise filter that I devised is both inexpensive to build and easy to put together yourself. (It costs less than $10 and takes less than 30 minutes to build!)

I once considered selling these devices commercially. I would have added an LED and a variable resistor and a variable capacitor to jazz it up, and I would have put it in a fancy box, but it would have been functionally what is presented in this article. I estimate that these devices could have been sold for about $50 to 65 each. Now you can make the device yourself, and pocket the savings!

The introduction of V.34 (28,800 bps), and faster modems has not generated as many complaints about these modem’s sensitivity to line noise as the move to V.32bis did. I don’t know if that is because the newer modems have better error correction capabilities, or because phone companies have installed better equipment, or a combination of these, or something else. The latest modems may be exhibiting less sensitivity to line noise because of better error correction routines, but the tradeoff seems to be that they are not running as efficiently, and thus as fast, as they might be capable of. Many users of V.34 modems are not achieving full 28,800 bps connections. Users of 33.6K bps modems rarely attain the full speed they are capable of , and users of 56K bps modems almost never get close to the speeds that their modems are advertised as capable of. Using a phone line Noise Killer might enable these modems to achieve higher connection speeds and throughput.

Before diving into this project, you should run a couple of tests to verify that your problem is actually being caused by line noise.

Here are some easy tests that you can do to determine if you have a line noise problem. Both of the following tests require that you use a text-based terminal program. A good terminal program to use for this purpose is ZTerm, which is shareware and can be downloaded from:

http://hyperarchive.lcs.mit.edu/HyperArchive/Archive/comm/term/zterm-101.hqx

The first test comes courtesy of 3COM. Go to this Web site and follow the instructions:

http://www.3com.com/56k/need4_56k/linetest.html

Unfortunately, this test has been known to give false readings. To back up the 3Com test, here is a line-noise test that you can do using the built-in diagnostic functions of your modem. This test uses Hayes commands. (The Hayes command set, also known as the "AT" command set, since most commands are preceded with an "AT", meaning "attention", is a standardized set of instructions that your modem uses to communicate with your telecommunication software. All modern modems use it. Though not all of them avail themselves of all of the possible commands, and many add an extended command set that is not implemented in a universally standardized way. Don’t worry. Understanding this little bit of tech-info isn’t necessary to be able to conduct the test. It’s very easy.)

1) Log-on to an online service (a local text-based BBS is ideal for these purposes) using your telecommunications program.

If your line noise problem is so bad that you can’t log on to a local BBS, you can probably hear it in the background during regular voice phone calls.

2) Once you are logged on, type the escape code that your modem uses to get into terminal mode while still logged on to the online service.

That usually is "+++" followed by a "return". Check your modem’s instructions to be sure.

3) Next, type "AT%Q" and hit "return". (This is the usual Hayes command to have your modem test the line. Check your modem’s user manual to see if your modem uses a different command.) Your modem will instantly test the line and report the quality of the connection numerically on-screen. 0 is the best score, 8 is the poorest (noisiest). 0 to 2 is considered acceptable quality. You can repeat this procedure several times for a better sampling. Keep in mind that line noise will vary from minute to minute, and that it may be drastically diminished or it may increase at different times of the day. Line noise may even be influenced by such things as the appliances in use in your house (all of which create magnetic fields that become current, and thus noise, within phone lines in close proximity to them), the weather, how many people are using the phone system at a given time, how far away the number you are calling is, what city you are calling, and who knows what else.

4) To return to logon mode type "ATO". (That’s an "oh" not a "zero".) You can now log off from the online service.

Another similar line noise test, for Supra modems, is detailed at:

http://206.156.108.200/products/support/techmine/mac/data/lnoise.html

Please be aware that even though you cannot get your 56K (V.90) modem to connect to the Internet at anything approaching the speed that you might expect, it may be that the problem has nothing to do with line noise. Call the repair department of your local telephone service provider (usually the number is 611) and ask to speak to a technician. Ask if your neighborhood has multiplexed phone lines or if there has been "pair gain." This is a method that is used to provide phone service to a neighborhood by splitting the phone lines so that there are enough to go around. If your neighborhood lines are multiplexed, your chances of ever attaining high internet connection speeds are slim. The device detailed in this article won’t help. In fact, short of having the phone company run a new copper line for you, probably nothing will.

Have a look at these Web sites for a more detailed discussion of troubleshooting your Internet connection problems:

http://www.teleport.com/~curt/modems.html

http://www.parkcity.net/support/modems/trouble.html#SPEED

Apple's 56k Page
http://til.info.apple.com/techinfo.nsf/artnum/n24482

Troubleshooting Guide
http://www.56k.com/trouble/connect.shtml

Simple things to try first to see if they will help improve your modem connection:

1. If your modem phone line is connected to a surge suppresser that is part of a surge strip, or UPS, disconnect it from these, move the line as far away as possible from these devices, and see if things improve. If they do, consider getting an in-line surge suppresser. Cheap surge strips are a very common source of line noise problems.

2. Is the phone line from your modem to the phone jack part of a tangle of wires behind your computer? Try separating the phone line wire from the rest of the wires and moving it as far away from the other wires as possible. Several feet, if possible. If you can't move the phone line wire away from other wires, do your best to try and keep this wire from running parallel to adjacent wires.

Why do I recommend this? If you can remember your high-school physics, when a current runs through a wire it creates a magnetic field around the wire. When a second wire runs parallel to the first wire, inside of this magnetic field, the magnetic field creates a current in the second wire. In this case this current induced into the second wire is noise created in your modem's phone line. If you can separate your modem's phone line from other cables, or at least try to keep them from running parallel to each other, you can eliminate a very common source of line noise.

3. The phone line cord used between the modem and the phone jack is usually cheap "silver satin" phone cord. IBM and Belkin sell a replacement that is much better at rejecting noise and maintaining signal strength. It has the same connectors at each end, RJ-11 modular connectors, but the cable itself is cat. 4 unshielded twisted pair. The same cable used in 10base-T Ethernet networks. For only about $12 I have seen these cables make a worthwhile difference.

4. If you are using a "Y" or other type of splitter at the phone jack, try removing it to see if things improve.

5. If you have any devices on your desk that use a large transformer, such as a florescent desk lamp, or a telephone with a mechanical bell, or a large CRT monitor, try unplugging them, or, at the very least, moving your modem and its associated cables as far away from them as possible. (Interesting Example: Have you ever noticed that your connections are unreliable in an intermittent fashion? Could it be that the problem only pops up when the refrigerator cycles on? You may need to get a noise filter for your refrigerator.)

6. There have been problems with connection speeds using the Apple modem script in conjunction with Apple internal modems that come with iMac and G3's and G4's, so many folks have switched to these script(s):

Ross's Scripts
http://www.taniwha.cwc.net/

If you determine that line noise is indeed your problem, it would probably be most logical if, before you go ahead and build this filter, you have your phone lines checked, and possibly repaired, by your local telephone company. Dealing with the phone company could be the basis for another entire article. I don’t want to go into that here, but a good source for articles with advice on the matter, and for ammunition to use when dealing with the phone company, is the Supra BBS at: 1-503-967-2444. You can access this BBS using the copy of Zterm that you downloaded for the phone line noise test.

Or you can view some of the documents from the Supra BBS on the Web at:

http://www.netdirect.net/home/tech/tel_line.html

http://www.umich.edu/~archive/mac/misc/documentation/oflinenoise.txt

The phone company will not want to be very helpful. Technically, all the phone company has to do is provide voice quality lines. They don’t have to give you lines clean enough for reliable high-speed modem communications. So, to get any assistance from them, you may have to claim that the background noise on your phone line is audible and annoying. (And, indeed it may be.) Also, unless you have a service contract with them, the local phone company is only responsible for the phone lines up to where they attach to your house, but not within your house. As a result, they will almost always claim that the problem is with the lines inside your house. You will have to stick by your guns and insist that you want the phone company’s lines thoroughly checked out.

The Device!

Now, if you have given up on trying to get help from the phone company, and you either know that you have a problem with phone line noise (or just strongly suspect that you do, you don’t have a lot to lose if you build this project and it doesn’t work.) you should read all of the following instructions and then gather up the tools and materials that you will need to assemble this project before you begin.

It is easy to build this phone line Noise Killer. You can solder the connections, or you can use an inexpensive crimping tool and use crimp connectors. (I prefer the latter myself. It’s faster and cleaner.) This device is really just a low pass filter, such as those used in radio tuners to reduce noise when listening to AM and FM stations. It uses a capacitor or two, which are generally good noise filters, and a resistor, and a phone line cord with a universal male phone jack connector. When done you can just plug it into your modem or into your phone jack and it does its job, thereafter requiring no attention. The standard comment that I get when I have someone listen on the phone line while I plug one of these devices in is: "Oh my! The phone line suddenly got very quiet! I hadn’t realized how much noise there had been in the background!" I hope that this device works as successfully for you.

To make it easier to assemble the parts for this project, I have chosen parts that are available at any Radio Shack and I’ve included their part numbers. Personally, when building this device I purchase my parts from the mail order catalog Digi-Key, because they have the exact capacitor and resistor values that I need without having to double-up on components, and their prices are lower also. Instead of having to use two capacitors and two resistors to achieve the proper values, as you do using parts from Radio Shack, using Digi-Key components you can reduce your parts list to only one capacitor and one resistor. Digi-Key will send you a free catalog. Their phone number is: 800-344-4539.

Parts:

 

If you want the ultimate in fine tuning and control, you can use variable resistors and capacitors in this project. But I have found that 2 MFD's of capacitance works well. (Any non-polarized capacitor should do: paper, Mylar, or metal film capacitors will all work fine. The caps should be rated at 100VDC+.3 since about 90 volts will be traveling through this device.) A total of about 2.7K ohms of resistance at a quarter or half watt works well. Unfortunately, Radio Shack doesn’t have single components that meet these specifications, so I have chosen combinations of components that will do the job. (Two 1 MFD capacitors wired in parallel, and one 2.2K Ohm resistor wired in series with one 560 Ohm resistor.) You can, once again, reduce your parts list to one capacitor and one resistor if you source your parts from Digi-Key and get components which closely approximate the necessary values.

You may need to purchase one #279-357 duplex modular connector. Don't buy one though until you've read the section on connecting the Noise Killer below.

Construction:

On the end of the 12-inch phone cord (part # 279-391) where the multi-colored spade-ended wires emerge, all the wires except for the green and red ones won’t be needed, so cut these unneeded wires off right where they emerge from the sheath of the cord. Use some electrical tape or (if you want to be fancy) some heat-shrink tubing, to insulate and seal off the ends of the cut wires. Cut off the spade ends of the green and red wires that remain. Strip off some insulation at the ends of the green and red wires so that there is enough wire exposed to either attach a crimp connector or to solder the end of the wire.

[Refer to the accompanying diagram for the next section.] Attach one end of both capacitors together and then attach that end to one end of one of the resistors. Attach the other end of that resistor to the other resistor. You may want to shorten the leads of the resistors first so that everything will fit nicely into the project box that you chose . Now attach the two free ends of the two capacitors together.

If it is easier for you, you can run wires between the components, making them easier to work with and attach to each other. Just make sure every lead is well insulated so that when everything is pressed into the project box, leads that are not supposed to touch do not touch. You will have to be careful about the length of the chain of these components if you want to fit it into a small project box. If you are willing to use a large project box, you can work with long leads, or extended leads, between components.

The box that you put this project in should be all plastic, so that it is well insulated, and you should be able to permanently seal the box either with screws or with glue. A lot of current will be flowing through this project when attached to the phone line, so you want to make sure that it cannot accidentally come open while in use. (This is especially important if you have small children.) I purchased several colorful plastic boxes that came in two halves at Tap Plastics in Sacramento on Florin Road. These boxes come in just about any size and shape that you want. (You can even get colored see-through boxes that let you see the components inside. These look really cool if you have done a neat job of construction.)

Radio Shack has a couple of plastic project boxes you can buy, but they are kind of large and klunky. If you don’t mind how this project looks, and you don’t mind a large box hanging out of your phone jack in the wall, one of these would be fine. DO NOT get one of the boxes with a metal lid. Get one that is all plastic.

You need to make a hole in the side of the plastic box for the wires to go through. Before you make the hole, check how everything is aligned once the components are assembled inside the box, in order to decide where the hole should be. Put the appropriate size rubber grommet in the hole. Run the wires through the hole and connect the free end of the joined capacitors to the green wire and the remaining free end on one resistor to the red wire. Carefully stuff the entire assembly down into the box. You may want to use some electrical tape or a dab of silicon sealer glue to hold the components securely in place inside the box so that they don’t bang around and come apart. Close and permanently seal the box. You are now done!

Installation:

You will need to decide where you want to plug the Noise Killer into your telephone line. It can be done in any of several places, these are the two best options:

A.) If your modem has two modular jacks in back, and one is free because it does not have a line connecting to a telephone plugged into it, connect the Noise Killer into the free jack.

B.) Technically, you should be able to plug the Noise Killer into any free phone jack in your house and it should work equally well wherever you install it. I prefer to have it close to my computer and modem in case I want to quickly disconnect it, for instance if I want to test and see if it is making a difference on a particular connection. This means plugging it into the same phone jack that your modem is plugged into. To do this, you will need to purchase a duplex, or Y-type, modular adapter. (Radio Shack part #279-357.) Plug the adapter into a phone outlet in the wall, plug the line from your modem into one side and the Noise Killer into the other.

Testing:

With your modem turned off, pick up your phone’s handset and listen to the dial tone. Plug in the Noise Killer. You might notice any of a number of things: a minor reduction in volume of the dial tone; a reduction in background noise; or no change at all. It all depends on how bad the line noise was to begin with. Actually, I can’t remember ever plugging this device into anyone’s phone line and not noticing some reduction in background noise. If you don't hear much difference when you plug the Noise Killer in, don’t let that bother you.

User your modem to connect to the Internet via your internet service provider. Try this several times, at different times during the day, and note whether you are now achieving faster, more reliable connections.

Author’s Note

The last time that this article was published (in the Berkeley Macintosh User’s Group Newsletter), the feedback that this author received via e-mail was interesting. Many people wrote to tell me that the device worked a miracle and to thank me. A few wrote to tell me that it didn’t work, a couple of the people who wrote to tell me the latter also were angry with me (I guess they thought that I had wasted their time), and one person wanted a detailed analysis of the theory behind how this device works.

Let me explain right here that I am a tinkerer, not an electrical engineer. I’ll leave it to someone else to explain why this device works. And I offer these plans "as is". I don’t guarantee that this device will work for you. All I can suggest is that it might be worth a shot. Please let me know how this device works for you (and be nice!) You can drop me an e-mail message at:

randy@mother.com

WARNING!:
DANGER! High voltage will be flowing through this project when it is in use. Be sure to permanently glue or screw this device shut before using and NEVER open it while it is plugged into the phone jack! Severe injury or death could result. Be sure to carefully insulate all exposed connections. Use only an insulitive plastic box for this project with NO metal sides.

About the Author of This Web Site:

Randy B. Singer is one of the co-authors of The Macintosh Bible (4^th, 5^th and 6^th editions), the world’s best selling book about the Macintosh Computer.

Mr. Singer also has a large Web site entitled:

The List of Law Office Software for the Macintosh Computer, located at:
http://www.macattorney.com/

Mr. Singer’s bio page is located at:
http://www.macattorney.com/rbs.html

Mr. Singer can be reached via e-mail at: randy@mother.com