More on Packet Radio

 Navigating packet radio can be very hard, especially if you're just starting out in the hobby. You may have questions like "What's the difference between APRS and packet?" or "Why can't I use X software for packet?" Heck you may even wonder how can you set up your own packet radio operation. Today, I hope that this blog post can put some of those wonder and questions to rest. So follow me as I delve into (hopefully) helping you get your start in the internet of amateur radio - packet radio!

First things first: the radio (node end)

To be honest, any radio will work for packet radio, be it HF, VHF, or even UHF like my node! It can be 2 channel or 200 channels - it all depends on what YOU need. If you need something that is as basic as it gets look into old commercial gear. Usually with software or hardware tweaks, you can get these radios to work in either the 2m or 70cm band. And they're a dime a dozen - since commercial gear went to narrow band, you can find old but quality Motorola radios for dirt cheap.

Look at interfacing options on your radio in question. The SM50 that I have running my packet network has a 16-pin connection on the back that supports everything needed for packet work - TX audio, RX audio, PTT and ground. To be honest, that's all you really need for packet work, and it doesn't require much to get things interfaced. For the heck of it, you can use something like the Easy Digi or build your own interface.

Lastly, look at power level and frequency range. VHF/UHF radios have much different propagation characteristics in comparison to HF radios. 5 watts on HF is A LOT DIFFERENT than 5 watts on VHF, and that's even different than UHF! Since I wanted something local, UHF was the perfect option. If you recall from my last post, the radio I have is set to 15 watts, and it covers the entire town of Maryville well with minimal dead spots.

The computer (node end)

Now this could be anything - a Raspberry Pi (yes, even a Zero!), an old laptop, an even older desktop...whatever you have! Personally, I picked a Pi Zero W due to its portability and the fact that it has GPIO pins for PTT, indicator lights, etc.

For an OS, go for Linux. Linux is so open source it's stupidly ingenious. Not only that, but most if not all packet software can and will run smoothly on Linux. Direwolf, the TNC software modem I use, runs at a max of 25% CPU usage on the Pi, and LinBPQ? A measly 3 or 4% uncapped! That equates to less than half the CPU used at all. 

Did I mention you could possibly use a Chromebook too?

Do keep in mind that this computer will need to likely run all the time. For my Pi, I have rules set that reboots it at noon and midnight every day. I've written a custom script as well that will cleanly start and stop both Direwolf and LinBPQ safely. So far I haven't run into any issues.

The computer (YOUR end)

Now before you ask me if you can use APRSDroid for packet work - NO.

Here's why.

Packet radio and APRS are two different aspects of ham radio. Yes, they both use the AX25 packeting protocol, but they use different frame formats. One sends a message, the other sends requests and information. One is formatted to include coordinates and a small message, the other is formally packeted with bits of data. So sadly, no - you cannot use APRSDroid on packet radio.

BUT...you can use Linux! Again! Linux natively supports the AX25 protocol (for some reason...) and it works REALLY WELL. So well I wished I would've discovered it sooner. 

To install, just run

>sudo apt-get install ax25-tools ax25-apps

This should be a good starting point. Next, you'll need to run

>direwolf -p

of course, in a different terminal window (assuming you have Direwolf installed already). Note the line that populates saying

>Created symlink on /dev/pts/X

Keep this noted. Next, go and edit axports by typing

>sudo nano /etc/ax25/axports

and add the following:

>ax0    KE0SBX    1200    255    2    Type something here for a note or something

This creates an AX25 port named ax0, belonging to KE0SBX (ThAt'S mE, replace with your call) at 1200 baud with a frame size of 255 and a window of 2. I'm not sure what the window is but 2 works for me I know! Also, in the last tidbit, add some information about the port connection.

Anyways, in your NON-DIREWOLF window, run

>sudo kissattach ax0 /dev/pts/X

where /dev/pts/X is the symlink that Direwolf created earlier. If all goes well, you should have a live connection!

To connect to a node, we need to use axcall, so type in the same window

>axcall ax0 <station that you want to call>

Now sit back, watch Direwolf run and key up, and boom - you now have a fully functional packet radio terminal!!!

Packet radio sounds so nice, it's like ASMR to my ears. Am I the only one who thinks so? ...anyone else? No?

If you want a REALLY minimalist build (trust me on this, it's like reliving the 1980s!!!) run your OS headless - you'll thank me later and it looks cool too. I'm running a test build headless at the moment (using Ubuntu server at a minimum install) and I must say it's really cool!

Unfortunately, native audio is a no-go on Chromebooks converted to run full-on Linux, so for an easy fix just use a USB soundcard, configure that in Direwolf, and that's pretty much it. For more advanced users, you can attempt to rebuild the kernel, but I won't detail how to do that.

Now that's not to say that Chromebooks can't be used for packet radio stock using only Crostini. Yes, by default these machines come preloaded without the AX25 kernel option. You'd need to go through and rebuild the ChromeOS kernel with AX25 support, but in all reality you don't even need it! John G8BPQ (the same gentleman who released LinBPQ et al) has software available called QtTermTCP which gives you the option to have an actual AX25 terminal that can connect to Direwolf, SoundModem, etc. via KISS TCP (easy) or AGWPE (more advanced). You can download it at his stable download page here. Keep in mind, he does offer this software in 32 bit and 64 bit compatibility and this works on Windows, Mac, AND Linux too! Yes, even bare minimum Crostini Linux!!!

The radio (YOUR side)

Even a Baofeng will work just fine.

No really. A standard run-of-the-mill UV5R will work just fine!

As long as you use 1200 baud, a Baofeng or any handheld will work just fine. The only caveat is you must make your own interface, which isn't hard if you understand how the Baofeng's PTT works. Spoiler alert - short the 2.5mm and 3.5mm sleeves together.

Any Yaesu, Kenwood, or Icom handheld works great too, and if you're a tech and that's all you have at the moment, you're perfectly fine! It doesn't take much to get started with APRS or packet radio, so just use what you have!

Conclusion

Packet radio has taught me so much about networking. A whole lot more than a college course on network fundamentals could ever teach me even! This is a great way to get started with digital modes, even if you just do APRS. 

As I write this, my node is 90% complete - I just need to wire the Pi up to the SM50 and put it on air! Here within the next few weeks, expect 445.925MHz in the Maryville area to come alive with AX25 1200 baud screeching!