Getting Started With Linux AX-25 and TCP/IP

AX25 Tips

The first thing I would recommend here is reading everything you can get your hands on before you start. There is a good chance that before you are done, you will have messed up your Linux distribution so bad, that you will have to re-install and start over (so by then you will know which sound card programs you don't like and won't have to re-install them) and they won't be taking up space on your hard drive. Yeah, I found this out the hard way.

FAIR WARNING! When you are done setting up the stack, you will probably be confused as to what worked and what didn't, so once everything is running use a backup program, and backup your system! Someday, you will want to re-install your OS to get rid of all the junk you couldn't resist downloading, and knowing that you will have to set all this up again will keep you running on an inefficient system for way to long. Yeah, I found that out the hard way too.

As you read up on your ax25 network, keep in mind things like nodes, servers, etc. that way by the time you start setting up the real thing, you will know what to get, and where it goes. As most networking people I have talked to say "Draw the damned thing out on paper" (I recommend in pencil, you will probably end up changing some ideas along the way). If you already understand networking you already have a big jump on the rest of us.

What works with the ax25 stack?

Well, first, let's cover the hardware side.

The ax25 stack will allow your TNC-2 "radio modem" to connect into the ax25 stack in "kiss mode" kiss means 'keep it simple stupid', and when you're working with ax-25, the simpler the better. You can also attach software modems such as Tom Sailer's wonderful soundmodem program to the ax-25 stack, so you don't need to buy a tnc-2, or another tnc-2. The soundmodem is also a great alternative to tearing up your expensive radios to make them work with 9600 baud fsk, if your radio can switch from rx/tx fast enough. There is also the baycom type modems, which are part hardware, part software. Using the baycom module for these modems allows a cheaper alternative when you need a hardware solution, and if you operate qrp, they are very small, use almost no power, and work.

Now for software side

Most of your packet software will run off the ax25 stack. This can be anything from a stand alone system like FBB, to Xastir, an APRS clone, or a simple splitscreen terminal program like linpac. I like linpac because I can hit CRTL/ALT/F2 log in as a user, start linpac, then hit CTRL/ALT/F1 and log in as another user and start X-windows. No matter what I am doing in X, the console mode linpac is listening, and if someone connects to me, it dings and I can hit CTRL/ALT/F2 and I am right in the terminal, quick. This is one of Linux's great advantages, multiuser. I can have programs running under several users at the same time, which means I can use different users to digipeat information from one network to another, etc. But, not to scare you, this doesn't have to get that complicated, and even if it does, that usually takes years to develop a system that large and complicated, and if you do, by then you will understand the ax25 stack much better.

Programs that use the ax25 stack can often be remotely controlled, or connected to the internet, or into a large convers server, lots of things are possible, but, first you have to get the stack to work.

Once you have an understanding of how it works, the best information I can give you is the program ax25-config. It will help set up the files you need to get your system working. It may be all you ever need. But, read the files it produces, and try to figure out how you would add other things you might want in the future. That will give you time to think about it, and by the time you are ready to add something else, if you ever need to, you will already have an idea of what is required.

A simple packet station

Here is an example of how simple your packet station can be.
A 2 meter fm transceiver (one of the old ones without CTCSS would work fine here).
A mic cable to connect the radio to the tnc
A Baypac or Baycom modem, which can key the handheld without other circuitry.
A laptop computer that will power the baypac modem (some won't), and your software.
A lightweight camera tripod to mount the rubber duck on, and it will act as a groundplane for the duckie.
A piece of thin coax to connect the antenna to the handheld. It is not a good idea to leave the antenna on the handheld, the mic cable is usually right next to it, and the rf goes straight into the computer via the modem. THAT IS A BAD THING! Keep the antenna at least ten feet from the radio/computer. I Found this out the hard way too!!!
That is it! I have used a station like this before on adventure radio trips, and it works great.
You could add a gps unit to the above setup, and now people could watch you hike or bike or sail, or drive around using APRS.
And, everything else you do to your network could grow from there. Of course, if you do this at home, with a desktop computer, you could use a regular large tnc-2 modem, external antennas, and better coax, but, the concept is the same.
Then, just let the network grow. You could write scripts to control your Cat system radio so that when you start xastir, the cat changes the frequency of the radio to 144.390 MHz for example, when you switch to the local bulletin board it runs your packet terminal and switches frequency automatically, and when you run say TNOS it would put your frequency on the TNOS frequency, and you are off to the races.... or ares..... or whatever. You control how simple or complicated you want the system to be.
It's that simple, and that complicated, the choice is up to you.

If you have any questions after reading this page, other people probably will too. Please send me an e-mail.   I am not a networking genius, but, if I can help, I will certainly try. And, that will give me information to make this page better, and isn't that what it's all about????

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Last updated by KF8GR Aug 9, 2004