APRS: digipeaters and gateways in MN

APRS is a location reporting system that uses two-metre packet and GPS to keep track of stations' locations. These stations can be displayed graphically on a map. For an idea of this concept, go to aprs.fi and enter your location so that you are looking at the metro area. Aside from showing locations, this interface also lets you view the raw packet data, bulletin board messages, and weather telemetry. You can also see the Maidenhead grid co-ordinates of any location by placing your mouse over that spot on the map, along with standard GPS co-ordinates. You can create an account and enter the location of your base station, which I can imagine would be helpful for HF and DX contacts to visualise where you are.

APRS is also one of the big tools used in emergency services, and amateur public service such as marathons. While two-metre packet has been in decline for decades now, APRS remains relevant. Like so many elements of ham radio, smart-phones can now use their GPS capabilities and transmit locations through the cellular data network without using two metres whatsoever. When ham radio is employed, a mobile or portable unit sends their location in packet form (AX.25) on 144.390, but unless it reaches the internet it's just a local signal. A digipeater can re-transmit that signal and pass it along to a larger area, but at some point, that information needs to get to an IGate. An IGate (or gateway) is a two-metre transceiver (or receiver) connected to a TNC and (usually) a computer with some kind of connection to the internet -- either through the land-line phone/cable system or through the cellular data network.

Now, when you are at aprs.fi looking at the metro, notice the icons on the top right edge. The sixth one down is the "filter" option. If you hold your mouse over the icon, you should see the word "Filter" appear. Click on that icon, and you'll see a menu. Uncheck "All Stations" and check the box marked "Igates". Now you'll see only the IGates.

There's not a lot of them, and they aren't optimally distributed. The south-east and north-east are particularly devoid of them. Sure, there are some digipeaters out there that help packets along in their quest to reach one of these stations, and there are satellites that infrequently pass over and "repeat" these signals. The hams running communications for events like marathons have their own portable digipeaters, but they still rely on these few stations to get their signals to the "outside world". Almost certainly, it would be more efficient to use the cellular network for this task, but that takes amateur radio out of the equation -- which is kind of the point, after all.

We need more IGates (APRS gateways) to keep the network robust. This isn't an incredibly difficult problem to solve, and it addresses one of the core functions of amateur radio itself.

Central MN digipeaters

Currently, the Gopher Radio Club's W0YC station is handling the majority of the packets, due to their superior antenna height and central location. That station, however, is experiencing difficulties. The GRC is not the only club or trustee in town with a tower, a two-metre radio, and an internet connection. Individuals, such as N0FKB, have stepped forward to use their home stations as IGates, and this helps to fill the gaps in coverage. Setting up an IGate would be a relatively simple way for a club to establish their "emergency services" credentials, and their sites are superior to most individuals'.

In my opinion, we don't need more digipeaters passing packets on to a tiny number of IGates; we need more IGates linking those packets to the rest of the planet.

Having a digipeater or IGate at a repeater site can also display repeater info in the packet data, telling people the frequency, offset, and PL tone. This can be useful to hams from outside of the area, assuming that they have APRS capability in their vehicle.

It's not difficult to imagine the utility of APRS to SkyWarn net control staff, either. Knowing the exact location of a reporting station can save valuable time and reduce ambiguity. Supporting the dissemination of that information via an IGate seems like a natural function of that effort.

Northern MN gateways and digipeaters

Southern MN gateways and digipeaters

I see repeaters as natural sites for APRS gateways (IGates), because they have relatively high towers and excellent reception range. Many repeater sites don't have internet access, however, especially in rural areas. In the metro, we have at least two VHF repeaters within Minneapolis proper. This means that they have access to the municipal fibre-linked wi-fi network. Other repeaters have EchoLink access, which would at least imply some kind of internet access. Certainly there are places relatively near digipeaters that have internet access, where a receiver could be employed for a gateway.

The current arrangement does seem to work, though the loss of one or two gateways or digipeaters, even temporarily, would change that situation. The addition of a few home gateways in strategic locations would increase the redundancy of the network, given that most homes have internet access.

Either solution -- home gateways or repeater-based gateways -- could work. Possibly a mix of the two is best. This isn't some huge investment in time and money, nor is it something that requires co-ordination and organisation. It's not a recurring cost, once it's set up, and low-tech solutions abound.

An interesting "how-to" article can be found here explaining how to set up an IGate (APRS gateway) using a Byonics Tiny-Trak and RaspberryPi. Another source of information is here, describing how to set up a gateway with (free) AGW APRS Digi software. A gateway doesn't require high-powered, expensive hardware. Any ancient desktop or laptop that's too under-powered to even load XP can be made to work. Likewise, an IGate doesn't put a heavy burden on your internet connection. You probably used more bandwidth reading this blog post than you would use in a day running a gateway. There's also a very old article here with links to very old software that can be made to work on win95 or elderly Macs. Once a gateway is set up, it doesn't require constant attention. It just silently does its job of bringing those all of those packets that are floating around home.

Another good source is here, with info on configuring different options.

Newer software, such as Dire Wolf, can work fairly easily with RaspberryPi and a SignaLink. This is a pretty good long-term option for experimenters. Bear in mind, however, that long-term solutions require a dedicated radio that's always on, with a dedicated antenna. And, given the poor building penetration of VHF, it would likely need to be an exterior antenna. If you are close to a digipeater, though, an interior antenna would probably do the job of getting those packets home.

Basically, a Baofeng, a Tiny-Trak, a Raspberry Pi board and wi-fi can be whipped into a gateway, although that's not a great long-term solution. Still, if you'd like to experiment and set up a temporary gateway in support of a public-service event or weather situation, you could contribute to the effort pretty easily. You can't have too many gateways, but you can have too many digipeaters interfering with each other. An IGate doesn't really need to transmit, so even an old analogue scanner could be your receiver, provided you can interface it with a TNC. As you can see, improving the APRS infrastructure is not a monumental task.

In theory, APRS can be used on UHF or 1.25M with these methods. The problem is that nobody is transmitting the APRS packet data on those bands. Certainly, you could set something up on those bands among a group using the method outlined by KD0WBK here, though using a radio for UHF or 1.25M on frequencies allocated for packet in the band plan. By using an IGate on those bands, the location data would be indistinguishable from packets sent on two metres, at least as far as aprs.fi is concerned. Once it gets on the internet, it doesn't matter what frequency was used to get it there.

I would hope that at least one club could scrounge up a junky old laptop, a cheap HT, and a spare SignaLink from somewhere and make at least a symbolic effort to support the APRS infrastructure. Failing that, even a handful of individual hams could accomplish the goal. Really, if your gateway doesn't transmit, someone wouldn't even need a licence to set up an IGate in their home or office.

Ultimately, if clubs and individuals fail to take this simple step to make APRS robust, I suppose that municipalities could take over the task. But it would mark a profound failure of amateur radio to support "emergency services" in their own community. Hey, maybe the Campfire Girls could handle the job.