15 April 2018

Packet Radio Is... Dead?

Google the term 'packet radio' and what returns are links to discussion after discussion on various ham radio forums focusing on the death of packet radio. Either packet radio is dead or it's dying, or its been dead for decades and why are you bringing this up again? Folks blame the internet, or cheap cell phones, or the slow communications speeds allowed under the Amateur Radio rules, or the antiquated gear, or global warming, or whatever.

There's truth in much of that. Cheap worldwide communications modes via the internet and inexpensive cell phone plans certainly have taken a bite out of the popularity of packet radio, but I think that's over-stated. For hams it was never about communications speed or the ability to instantaneously update your Facebook status so friends on the other side of the globe know which new puppy video you 'liked' this morning. It was about the technical challenge and building robust communications backbones. Packet radio is a digital point-to-point communications protocol, and if you buy the 'internet killed packet radio' line how do you explain the exploding popularity of low speed digital modes on HF?

But first, what is packet radio? The concept is simple; packet radio is the process of bundling digital data (ones and zeros) in to 'packets' of data and sending them out over the airwaves. The make-up of the data packet is controlled by the digital protocol used, and the protocol may add additional information to the packet as it is sent. For example, the standard UHF/VHF packet protocol, AX.25, adds the originating station's callsign, any digipeater routing information and the receiving station's callsign to the information packet as it is sent. This gives any digital repeater (digipeater) the information it needs to move the packet on to its intended recipient station. Some protocols, like D-STAR (discussed below) embed forward error correction blocks to the packet stream to ensure the data is not corrupted in transit. Generating packets is normally done using a terminal node controller, or TNC, connected to a radio which is in turn connected to a computer running one of a number of packet radio applications. A TNC is simply a radio modem that takes an audio signal generated by the packet radio software, and converts it to a digital signal and sends it out over the air. The TNC generates the 'packets' based on the packet protocol used.

The digital communication protocol traditionally used for packet radio - AX.25 - is an old standard that lacks error correction. A new standard with forward error correction was introduced by TAPR about a decade ago (FX.25), but adopting that would mean wholesale abandonment of existing packet gear, and hams are notoriously cheap and will cling to whatever works for as long as possible. So the old AX.25 standard soldiers on, but it is soldering on a shrinking battlefield where fewer and fewer Amateurs are getting involved with VHF or UHF packet.

When I stepped away from Amateur Radio almost a decade ago packet radio was already dying. I used to run a packet station (a VHF radio slaved to an external TNC) and played around with packet bulletin board systems (BBS) and the new-ish Automatic Packet Reporting System (APRS). Playing on the packet systems was fun - hopping through digipeaters to get to the station or BBS you wanted check in with. There were digipeater networks that spanned the southeast, and as long as you could get to a local digipeater on a tall enough tower you could in theory 'talk' from Atlanta south into Florida or north into Kentucky. The AX.25 standard, at 1200 baud, was fast enough to support real-time keyboard-to-keyboard chats or, if you checked in to a BBS somewhere, to send or retrieve short messages.

When I stepped back in to Amateur Radio a little over a year ago I was saddened but not surprised to see that packet radio as I knew it was dead. Tune around to the old packet radio frequencies on 2 meters and all you'll hear is dead air. What happened? Well, as I said earlier, the internet, expanding wi-fi services, inexpensive cell phones and rate plans, web-based global email services like GMail, and social media sites like Facebook are partly to blame. Then there's the overall decline in interest in Amateur Radio. In the Atlanta metro area the local voice repeaters sit unused for much of the day, and even the flagship repeaters like W4DOC in downtown Atlanta are silent most of the time.

Some of the blame also goes to new digital modes on HF and UHF/VHF. Hams are like crows - they are attracted to shiny objects, and HF digital modes are big, shiny objects. What helps is that if  you have the gear needed to work one digital mode, an HF radio, a sound card interface and a computer, you have the gear needed to work them all.

A decade ago, on HF, you had RTTY and the new-ish PSK-31. There were other digital HF modes out there but these two were the dominant ones. RTTY was an old standard, predating WWII, but it worked and was great for keyboard-to-keyboard chats. PSK-31 was hot, hot, hot - everyone was getting in to PSK-31. It is a very robust comms mode, used little transmit power, wasn't a bandwidth hog and permitted either traditional keyboard-to-keyboard chats or communications via macros. I believe it was the success of PSK-31 that spurred the development of other digital modes, particularly weak signal modes like JT65 and JT8. For many hams, working HF digital became the all-consuming passion and they turned away from UHF/VHF packet with it's clunky telnet interface and heavy dependency on point-to-point infrastructure.

But things had changed on the UFH/VHF bands too. When I stepped away from Amateur Radio we were just beginning to hear of a new digital standard under development by the Japanese Amateur Radio League called D-STAR. The Japanese amateurs saw the need for a narrow-band digital FM protocol that could carry voice and data. D-STAR is an open protocol with a heavy dependence on the internet. While direct radio-to-radio or local repeater chats via the D-STAR protocol are possible, D-STAR is mainly used in the 'reflector' mode here in the US - a local D-STAR node (or repeater) is connected to one of several internet-based reflectors so that all stations linked to that reflector, regardless of location, can pass traffic. This means that an Amateur Radio operator in Atlanta talking on D-STAR on a local node tuned to reflector 30C can talk to another ham radio operator in Sydney, Australia who's local node is also tuned to reflector 30C (and I've done this). But D-STAR is mainly a digital voice mode, not a data mode. Data can be sent over D-STAR, but most of it is throttled to 1200 baud by hardware restrictions. D-STAR can support APRS-like functionality and be used in packet chat and BBS-like modes using a program called D-RATS, but D-STAR as a digital packet tool seems to have been slow to catch on. The reason? Most likely the near wholesale adoption of Winlink.

Winlink deserves its own separate discussion and I'll cover it more fully in a later post, but essentially Winlink is world-wide email over radio. The system was developed in the 1980's mainly to support sailors, missionaries and other individuals and groups who didn't have access to traditional email services. It is extremely flexible and can use a wide variety of protocols (including AX.25) to 'get the message out'.

Winlink has been adopted wholesale by emergency response services across the US, including Amateur Radio emergency groups like ARES. One of the most common protocols used for sending Winlink emails or messages is (from what I can see) the AX.25 protocol riding on the 2 meter HF band. This means you need a packet TNC to run Winlink on VHF, and I suspect Winlink drives the majority of TNC sales these days.

So packet radio really isn't dead. Old applications for packet, such as BBS systems, have died off, but new ones like Winlink have come on line. No, packet's not dead - it's just carrying on in other ways and in other formats.

W8BYH out


  1. I stepped away from ham radio for about a decade myself, and was active in VHF packet, HF Amtor and Pactor. I had a lot of fun with those modes and in the back of my mind I think we still need to stay sharp with this stuff as one day we could actually need it again. I'm going to hang onto my Kantronics KPC-3 anyway. I sold my old KAM but I may dabble in PSK-31 and get my feet wet again. thanks for writing this, it was just what I needed. 73 DE N0MIN

  2. Excellent article. Very interesting to read. I really love to read such a nice article. Thanks! keep rocking. Two Way Radios on the Market

  3. Great article - thank you! 73 DE KN6PH