Make your own null modem cable

Make your own null modem cable

One of my coworkers needed to make a null modem cable last week, and most of the sites he found made it far, far too difficult. Here’s how to make your own null modem cable.

Most of the time, you only need three pins. In fact, I never needed more than three pins, no matter what I was connecting. Usually, a 3-wire null modem cable is more than sufficient.

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Improving DSL speed

I found some DSL speed tips. They work. If you have DSL, you should read them and do the same.I went from speeds all over the map to a fairly consistent 600 kbps just running a new CAT5 line for DSL. Replacing the cheap, flat, old-fashioned phone cord running from my modem to the phone jack and the other cheapie in my patch panel with UTP phone cords boosted me another 30-50 kbps. That extra boost varies, but it’s something, and I’m glad to be consistently above 600 kbps now.

Finding UTP phone cords is a challenge. Supposedly Lowe’s has them but I can’t verify that. I had one that I wasn’t using for some insane reason. I found another one at a garage sale, obviously from a DSL installation kit. I don’t remember what I paid for it, only that it was a lot less than it’s worth to me. Digging through boxes of random cables at garage sales can pay dividends.

The easiest way to get them is probably to make your own from scrap lengths of CAT5/5e/6 cable. Just crimp RJ11 modular plugs onto the ends instead of RJ45. Radio Shack sells a package of 10 plugs for $6. Overpriced, but convenient. There’s always a Radio Shack nearby.

Belkin sells a special shielded twisted pair modem cable as an “Internet cable,” for around $20. I’m sure it’s a very good cable, but it’s not worth 20 bucks.

When looking at a store, as a general rule, flat cables are always bad, but a round cable stands a chance of being good.

If you have a fairly new house, chances are your phone wiring is pretty good, in which case the most important thing is getting a good phone cord. If you have a house built in the ’60s like me, with phone wire run after the fact by a weekend handyman who either didn’t know or didn’t care how to avoid interference on the wires, that’s another story. If there’s 30 feet of bad wire between the telco and the modem, the quality of that last 6 feet of wire doesn’t make much difference.

While you’re at it, you might as well replace all your phone cords with these higher-quality models. Your voice calls will be clearer, and it eliminates the possibility of those cables introducing interference into the line. That interference shouldn’t reach the modem, but “shouldn’t” is no guarantee.

New wiring

Gatermann and I spent most of the day pulling CAT5e through the house. It’s long overdue. The guy who wired the phones in the house broke every single rule I could find about running voice/data cable, and it wasn’t good stuff to begin with. Plus, I was really tired of the lack of reliability of 802.11g in this house. Why I can see all of my neighbors’ networks but not my own is beyond me.Running a single CAT5e line from where the phone network comes in over to the center of the house made a huge difference. The phones sound clearer, the DSL is much faster (consistently 630K now–it used to dip to 300K frequently) and running lines is much easier when you’re away from the circuit breaker box and not surrounded by power cables everywhere.

At present I only have two rooms networked, but it’ll be easy enough to add to that as needed now.

Wireless is convenient, but 100-meg is very nice. It’s reliable and fast. Gigabit is even nicer. Now it would actually be practical to upgrade to gigabit. At gigabit, network resources run nearly as fast as local ones.

I wish I’d done this years ago.

Wiring the house

My trusty Linksys WRT54G started dying yesterday. I think I’ve had it 3-4 years, so it’s had a decent run.

I have some temporary wiring in place until I decide what I want to do, but I really think I want some wired Ethernet.For one thing, my phone wiring is really bad, and I think that’s affecting my DSL speed and reliability. Modern CAT5 wiring would solve that problem neatly. And if I ran a dedicated unfiltered line straight to the modem and filtered lines everywhere else, I could get by with just a single line filter, instead of a half dozen. That should improve reliability too.

And while I’m running CAT5, I might as well run two wires, so I’ll have convenient network jacks in several places in the house. And if I’m running wire, I might as well run CAT5e and get gigabit capability. That should give me faster and more reliable networking, both locally and online.

The project would take about $100 worth of cable and jacks, I estimate. I already have plenty of jacks, so I’d just have to buy a spool of CAT5e. That, and find the time to run it.

I may keep wireless around for ultimate convenience (a combo DSL modem/router/access point costs about $70, which isn’t much more than another WRT54G, and my modem is getting old too), but I like the idea of having my desktop PCs connected via gigabit. It’ll make sharing drives more practical, and potentially much more secure if I get fancy with network segmenting and firewalling.

I think I’m going to be asking the network wizard at work a lot of questions… Good thing he sits right next to me.

And now mostly I need a free weekend to do all this.

A day of catching up

I might finally have reliable DSL. Gatermann and I spent a good part of the day cleaning up my phone wiring. The wiring appeared to have been done by someone who couldn’t make up his mind how he wanted to do it. Seeing as I had two jacks that didn’t work anyway, and I own exactly three telephones plus an answering machine, we pulled out a number of the runs altogether (the wires are still there, just not hooked up at the box). And we cleaned up some oxidation that had shown up on some of the lines that were there.
My DSL connection does seem to be more reliable as a result. We’ll see in time how it turns out, but I know the brief storm we had tonight would normally knock me off the ‘net, and I haven’t fallen off yet since we did the work.

We also rebuilt a system. I’ve been intending to rebuild this one for some time (I pulled the case out of storage months ago) but never got around to it. Anymore, it seems like it’s a lot more fun to mess with other people’s computer projects than with my own. Anyway, we pulled out the system that served up this web site up until about a year or so ago (a Celeron on one of the last of the AT motherboards, a socket 370 job from Soyo), removed it from the old Micron case I’d put it in, and we put it in a monster server case, a former Everex 486/33. It’s a really good-looking case–battleship gray with black drives. And it’s built like a battleship too–very heavy gauge steel. It was pretty funny when we pulled out the full AT motherboard that had been in there and installed the Soyo, which is even smaller than what we used to call baby AT. We installed my CD-RW and DVD-ROM drives and a few other bits and pieces, and… an ISA video card. Yes, I’m sick. I was out of PCI slots and I loaned the AGP video card for the system (a Radeon 7000) to Steve last week and won’t be able to meet up with him to get it back until Wednesday at the earliest. I am half tempted to go ISA for either the sound or network card for the time being in order to free a PCI slot for an Nvidia Riva 128 card I have kicking around. It would be a big improvement. The screen writes remind me of BBSing; the text comes onto the screen at a rate somewhere between what I remember 300 bps and 1200 bps looking like.

But then again, what I want this system for (primarily) is to do things like burn CDs, and I don’t need superfast video for that. And I don’t know that I’m going to be burning anything between now and then.

Yes, I know, catch-up days are terribly exciting to read about.

But somewhere around here I think I have some stuff I wrote last week and never posted. I’ll have to see if I can find it to post tomorrow.

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