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Picture of Solar Powered APRS Digipeater for Amateur Radio

This instructable will show you the steps I took in building a solar powered APRS amateur radio digipeater. Some of the info presented here can be applied to other projects that require power in remote places or where utility power is flaky.

It's assumed you have some tech background, basic tools, basic electronics knowledge, and of course some common sense. An amateur radio license is required to transmit on amateur radio frequencies. The license is not hard to get and there are plenty of study materials out there. A search for "amateur radio license study materials" or "amateur radio practice exams" should yield some results.

Step 1: What's APRS?

Picture of What's APRS?

APRS can be most easily described as amateur radio's version of lojack. Yes, this description tends to annoy some diehard hams but it really is the best way to describe APRS to someone that is not a ham radio techie. APRS stands for Automatic Packet Reporting System. Packet referring to data packets that are sent via amateur radio frequencies as data chirps that can be heard with a receiver on the correct frequency. These data chirps contain information on the sender's callsign, their location, and short amounts of text which can be additional data like that from a remote weather station or relay of someone else's data.

In short, APRS can not only be used to keep track of vehicles both on and off our planet (the ISS beacons an APRS signal that can be easily picked up with basic gear), it can also be used to send telemetry and messages.

As a licensed amateur radio operator in the USA, you can take advantage of the APRS network to keep track of your car, boat, plane, weather balloon, or other moving object. You can also use the APRS network to look at weather data from the thousands of amateur weather stations that are out there. While APRS can be used to keyboard back and forth much like instant messenger, it's most popular use is showing the position of moving objects.

In order for this whole network to work, it requires users with the proper gear and digipeaters. A digipeater is a digital repeater. The digipeater listens for data chirps that have been encoded with instructions to retransmit them and then retransmits what it hears when appropriate. This allows users with mobile or portable APRS stations to cover a wider geographic area. This is how a network of radios can send data back and forth for long distances without needing an internet connection. A digipeater can be a standalone dedicated device or it can be a feature incorporated into some of the more high end VHF amateur radios.

The internet is not totally banished from APRS land. It's actually blended in as an additional resource. Stations called I-gates can take traffic heard on the radio and bounce it over to the web allowing users with no APRS gear to still see what's going on. The pic above shows APRS traffic in South Fl via the APRS.FI website. Some I-gates are capable of taking APRS traffic from web based applications such as APRSdroid and putting it out on radio frequencies. This does get a little more complicated though as all users transmitting on the radio side must have valid FCC licenses. By interfacing with the web, it allows users to view APRS traffic will beyond their normal radio range. Should the web side go down though, the APRS network continues to work solely on radio providing there's enough stations within digipeater range.

In the USA, the popular VHF APRS frequency is 144.390Mhz. You can listen in on a radio scanner for data chirps and even decode them with simple software. You dont even need a computer. There are apps out there for both android and apple. There's no need for an amateur radio license if you dont plan on transmitting so if you're just curious, you can get your feet wet in the hobby with just a scanner radio and an old cellphone. If you just want to look at the web side of things, try the APRS.FI website to see what's happening in your area.

Why solar? I could easily have left this running off utility power and actually that's how it started life. Ham radio is a hobby with a strong emphasis on self sufficiency. Unlike utility power, the Sun always comes up regardless of what mother nature has unleashed.

APRS is fun to watch as folks drive around but it can have some very important uses. In times of disaster when street signs are gone and places look unrecognizable an APRS user can be guided to a destination in real time by another station viewing their movement and it can all be done without a cellphone network. APRS is also useful for keeping track of assets such as ambulances, food trucks, bike repair techs and so forth during large marathons or bike races.

Without digipeaters, the coverage area of the APRS network would be nil. Just like any other hobby, there's always folks out there doing things for the benefit of the hobby and that helps keep things going.

chichimus1 year ago

Nice project. I have been thinking of putting an I-gate up in the top floor of my shed with a solar panel outside. We have reasonable coverage here but I live down in a small valley so there are a few gaps locally. If nothing else it would allow my wife to follow me on APRS.fi when I am out rambling about :)

ggriffith11 year ago
Nice article.
I have been running a solar powered 2m repeater for over 20 years, and your instructions will help many people. I also almost remember using packet radio prior to the internet.
But I wonder why you use a gain antenna. I built a yagi for packet but only to reach the nearest node station which was over some hills. But the repeater always used verticals to get all round coverage.
Regards. VK3CQ
ke4mcl (author)  ggriffith11 year ago
I used a vertical gain antenna to get omnidirectional gain. The goal of my setup is to pickup local stations and be able to bounce them along to the next digi for extended RF coverage.
Wild-Bill1 year ago

Cool - I feel that the Internet has had its effect on reducing the people who might have become interested in HAM radio. I find your project fascinating and I have just learned some thing new. Years ago I looked at building a repeater based data transfer system for a forest products company (I was the IT weeny). The idea was floated to me by by a HAM who developed a business creating remote security monitoring systems. I encountered him as he was looking into real time open source video compression. Unfortunately my company wasn't willing to consider the proposal. It would have been so simple to pull off using just handhelds. We already had most of the physical locations (for out radio network) and we only really needed one new location to get the data network to work to fully cover out operating area, thinking of things like remote portable cutblock weather stations. I never thought of using it to monitor the logging trucks. I think, that the potential scope of the project and what it could do for the company, scared them. Looking at the APRS.fi is interesting. Thanks.

ai4px1 year ago

Very nice! You know what would be cool? Co-locate it at your local 2m repeater site and use the discriminator audio from the input freq of repeater to feed the input of the TNC. Then you could scavenge mic encoder packets from the 2m input and spit them back out onto 144.39. Bonus points if you tie the carrier detect LED to mute the audio going into the 2m repeater, especially if the repeater has an audio delay board in it.

ke4mcl (author)  ai4px1 year ago
Would be a cool idea but repeater owners and just ham activity in general in soflo is kinda weird. We just don't get the general comraderie amongst system owners here like they have in other parts of the country. Sadly you either have to rub someone's ego or just build your stuff on your own. We have a repeater and aprs digi on a 1200ft tower within visual from my place. Its all been busted for well of over a decade and nobody can get up there due to politics. Just an all around bummer.
MikeD111 year ago

Check out the LiFePo4 batteries. They don't explode like the other Lithium technologies. $145 will get you 80 5AH cells that can be put in series (4) to get you 12.8V so you'll have a 100 amp hours at 12.8V battery. Best thing is these battery's can be charged/discharged many thousands of times. They way outperform lead acid! Just don't go below 2.8V on any cel or will wreck em.

ke4mcl (author)  MikeD111 year ago
I've been messing with lithium's but on a smaller scale. I know they can pack plenty of punch but paid $25 shipped for the 20Ah 12v SLA in this project. Hard to beat deal on Walmart.com
SamWoT.1 year ago
Wow, nice and thorough and easy to understand
Tominaz1 year ago
wow great project, I'm sure the folks in your area will appreciate the added capability