Packet radio is is supercool!
It’s been around for a long time, but the idea of sending digital data over wireless radio links is still intriguing even today. Know that your modern smartphone is nothing more than a computer which can transmit and receive digital data over the air. Of course it’s capable of sending voice as well, but it converts that to and from a digital form. The point is, many folks take these capability for granted now.
The allure of packet (digital) radio is the ability to intimately control the process of digital wireless reception and transmission. We get to choose the radio band and frequencies, be it VHF, UHF, or HF, we get to choose the modem transmission protocol, i.e. AX.25, VARA, PACTOR, etc., and so on. We get to tinker with all of it. That’s what ham’s do.
Lately, I’ve been using the Winlink email system.. Winlink allows the sending and receiving of email over radio. I’ve been using (mostly) the VARA FM packet protocol over VHF through a digipeater located on Sandia Crest. I can’t reach the Winlink mail server directly as it’s on the other side of the mountain and so it can’t hear me. The digipeater on the crest can and so it relays my data packets to the mail server on my behalf. Awesome. I’ve also experimented connecting long distance to a Winlink mail server via VARA HF packet protocol. Ships at sea often use an HF packet link to send and receive mail as HF can work over hundreds and thousands of miles.
Other things I’ve fiddled with is trying out packet data using traditional amateur AX.25 packet protocol. This used to require an external packet modem like the ones above to interface between your computer and radio, but today we generally use a software program called a sound modem which is a simply a modem implemented as a PC application rather than a hardware device. Since my PC connects to my iCOM radio via USB, and the USB connection carries audio in both directions, setting up a modern radio to talk to a computer is simple and straight forward.
I’ve been playing around with the Automatic Packet Reporting System (APRS), which uses an AX.25 packet modem to send position and telemetry data over the air. I’ve been especially interested in using the DireWolf sound modem because it can interpret the incoming data and display it in a simple text form.
There are so many new things I can now do using packet radio, it is hard to list them all. In the next post, I’ll introduce radio repeater linking on the AllStar network using the Asterisk PBX system, modified for amateur radio. I’ve got that all running on a raspberry pi and it’s awesome!