This article is Part IV of a series called Track Your Adventures for Free where I outline how to use Ham Radio and your Smartphone as an affordable APRS tracking system. For reference, here are links to the first 3 parts:
In part III we modified a smartphone headset and our Baofeng UV-5R headset to create an interface between the speaker and microphone of the two devices. As a refresher, in part I we discussed how APRS works using digital packets that are encoded in analog signals. The ham radio will receive these analog signals, which are audible to the human ear, and we must get these analog signals to our smartphone so it can decode the digital packets of information that are encoded in the signal. These packets will contain the APRS position and identification data from transmitting stations. On the other side of things, our smartphone will also use its internal GPS to determine your current position, and then use this data to create an AX.25 encoded analog signal that it will send to the ham radio to broadcast your position. Great, but how do we accomplish this?
The answer, for Android based smartphones, is to use a piece of software called APRSDroid. It is available on the Google Play store for $4.99, lifetime updates included via the play store. However, the developer also provides the software for free on the APRSDroid Website. You can download the APK to your Android phone and install it outside of the market at no cost to evaluate it. Just keep in mind that because it was installed manually, updates will not come via the Google Play store like other apps. You will have to keep track of new releases as they come out and manually install them. I recommend purchasing the app once you have evaluated it and made sure it works out for you simply to support the developer in his great work and also to ensure you always have the latest version.
After you install the application either manually or purchasing it on the Play Store, open the application and you will be greeted with the following:
For many of you, this will probably be the first time you hear about APRS-IS. APRS-IS (Automatic Packet Reporting System-Internet Service) is the common name given to the Internet-based network which inter-connects various APRS radio networks throughout the world (and space). APRS-IS is maintained and operated by volunteer Amateur Radio operators to provide world-wide capabilities to the Amateur Radio APRS RF networks and to promote the Amateur Radio service as a whole. Because you will be injecting information into the APRS-IS system, which is designed for licensed amateur radio operators (Hams), you must be properly identified to obtain the privilege. Assuming you do not already have an APRS-IS passcode, you should click on the “Request Passcode” link to continue.
Continue reading Track Your Adventures for Free – Part IV – The Software
Adventures are meant to be shared! But for those of us in the Overland community, our adventures often take us to places where there is no voice or data reception. While smartphones have the ability to beacon your position to share with friends and family back home, they are only as effective as your carrier’s coverage area. Most people make the switch to a satellite based tracking device such as the SPOT Connect or InReach to fill this void. However, these devices require that you pay a subscription for both their emergency beaconing features, and an additional fee if you want to track your travels. This isn’t always cost effective, and comes with several limitations.
A trend we see among the Overland community is that most are licensed ham radio operators or have plans to become licensed. Those who are licensed can take advantage of the Automatic Packet Reporting System (APRS) that is deployed all over the world through a network of volunteer ham radio operators and organizations. APRS is a digital communication system designed to support several tactical communication objects, one of which is Global Position System (GPS) data. The network is formed by a collaborative deployment of digital repeaters (digipeaters) that listen for packet data on the designated local APRS frequency. In North America, that frequency is 143.390 MHz, and if you tune your radio to that frequency you will hear the AX.25 protocol frames being transmitted much like an old modem or fax machine sound. The digipeters listen for local signals and re-transmit them at a higher power to propagate them over long distances much like a traditional voice repeater works. However, APRS packets can go through a specified number of hops through various digipeters, and this is selectable via the “PATH” instruction in your digital packet. Using PATH, you decide how far your actual transmitted signal is physically repeated on the network. This gives you some control over how your position beacon packets propagate. Most importantly, your packet will usually hit an APRS Internet Gate (known as an iGate) that will connect to the APRS Internet System (APRS-IS). APRS-IS is the reason why you are able to share your data with others, because your position packet data is then available on the aprs.fi website and that information can be accessed accross the world by anyone with an internet connection and who knows your call sign. It is important to note that APRS does not require the internet, that is just a bonus. It can work from radio-to-radio, allowing groups to track each other real-time. This again, highlights the use of PATH because of the geographical location of your group members. If you are all within 50 miles of each other, then a single digipeter transmission should cover your group, but if one is 100 miles away you would want to increase your PATH to ensure that your radio waves reach their particular radio.
Continue reading Track Your Adventures for Free
Safety is important to us, and we chose to use a SPOT CONNECT Satellite Messenger as a fail safe device in case things go wrong in the field and we need urgent help. The SPOT device was designed to be versatile, portable, and rugged. A part of achieving portability is to function using batteries — very specialized Energizer Ultimate Lithium batteries that are expensive and difficult to find in more remote cities. Our SPOT device sits inside of our vehicle 99% of the time, and yet we were still consuming a pair of these batteries every 4 days when using the active tracking features. We were surprised and a bit disappointed that SPOT did not offer a 12V vehicle power option, since the performance of the device would be more reliable having a consistent power source. After further researching the device, we decided to develop a solution that would retain all portability and ruggedness of the SPOT device while allowing us to plug it in to the vehicles power.
The first step in the development process involved figuring out just why SPOT insists that the device be used with the Energizer Ultimate Lithium batteries exclusively. We wondered if it was a result of needing a specific steady voltage over the battery life cycle, or if the current demands from the SPOT device were too much for a standard lithium battery. So we opened up the device to take a look at its insides and do some testing. You start by taking the back cover off your SPOT device and removing the batteries. The first thing you notice when you start the tear down is another warning on the circuit board that reads: “AA Lithium Batteries Only.”
Continue reading Hard Wiring a SPOT Device