APRS is the Automatic Position Reporting System. It uses amateur radio dedicated digital communication to send out your position in real time.
There are almost 10,000 APRS users around the world (and growing) using devices like a handheld transceiver, mobile rigs and/or home stations with GPS receivers connected to computer TNCs or built into motherboards to report their position via RF anywhere from once every 5 minutes to every 6 seconds depending on what you configure it for.
These reports get picked up by other ham operators with receiver equipment who can forward them via internet gateway's like aprs.fi, HamQTH and others where they will be displayed on any device connected to these servers pretty much anywhere in the world.
This makes APRS a great way to send out real time position reports and make them visible to others. This also makes it a great emergency communication tool as well, since ham radio operators and emergency groups like ARES and RACES use APRS for sending messages back and forth in the field via these reports that can be shared instantly on any internet connected device or server.
Ham Radio APRS - What is it Good For?
APRS is deigned as a low power consumption (and therefore long range) digital data link between Amateur Radio stations using RF on the 2 meter band upwards CW/USB channel with 4800 baud FM APRS with telemetry applications, SSTV frame stores etc.
Since its inception back in 1994 by Bob Bruninga (WB4APR) it has become an invaluable tool for many hams around the world.
Some make use of this digital data link by putting up dedicated digipeater stations hooked to GPS receivers, others build their own station rigs and antennas capable of sending out position reports every few minutes.
Others yet do nothing more than connect a TNC or KISS tuner (or even just a sound card) to their radio equipment at home relaying position information in real time via internet gateway servers like aprs.fi which is not only a great help for other amateur radio operators using APRS, but also comes in handy when you need your position to be visible on Google Maps or Google Earth for example.
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How do you use Ham Radio APRS?
- Any ham radio station can receive and forward APRS packets to other stations.
- A mobile station with a GPS receiver and TNC in the loop may send position reports once every 2 or 5 minutes, if configured to do so. An OOS (Out of Service) station sends the same kind of reports at 48 seconds intervals typically.
- A fixed station sends position reports every 10 minutes, by default, which is often considered old fashioned.
- More advanced modes like APRS Messenger offer proportionally more telemetry like bearing/direction from fixed stations to others that request such data usually via APRS-IS (internet system). You may choose how frequent your texts will be routed through the internet with this mode by adjusting settings it provides.
- A station may be configured to send out different packets on different radio channels and not just one stream of reports like most digital modes these days (such as: D-Star, Digital Voice mode etc) that works on a single RF channel only which can result in breakup if you're out of range for too long. With APRS you can choose where to emit your packets and how often they repeat (three times or hourly). You can also configure digipeating paths (e.g.: /i during the night) to avoid overcrowded areas with static packet reporting stations running 24/7 sending out their packets without reprieve.
- Finally, APRS is capable of sending bi-directional "comments" ("text messages") directly to other stations on the network. This makes it suitable for exchanging quick reports ("CQ de (call)") or packet chat (via APRS-IS servers like aprs.fi which you can use even while not connected to an RF channel). Unlike some digital modes, this mode actually uses addition inter-channel delay to avoid collisions above the noise level due to distant transmissions of packets that are delayed from your local copy.
Logging into APRS & choosing what you want to see:
APRS has been around for a long time now and many different sites have sprung up along with several different programs designed for monitoring and decoding APRS traffic in one way or another.
Most popular services these days include: aprs.fi, APRS.fi, OpenAPRS, Amprnet.org, PozTrack.com etc to name a few...
APRS network map including "The Big Picture" site - aprs.fi
If you have an 'always on' internet connection at home or even just by your mobile station's location I highly encourage you to get acquainted with these services especially because they are mostly free of charge!
The real-time data they provide is very useful for ham radio operators trying out digital modes like APRS Messenger or DigiPan software for example or even if you're into satellite tracking (ISS, NOAA weather satellites etc).
What is the frequency for APRS?
Just like with any other digital mode, APRS works on a single frequency at a time which you can see in the map above, but since most of the network is concentrated around 144.800 MHz in Europe and nearby countries you'll usually find it there or one of the nearby channels instead if something unusual was to happen in your area for example (covered more later).
Just remember that APRS doesn't have a dedicated channel so any ham radio operator may join in including mobiles which is why some repeaters (and even DMR services) are starting to carry this service over their analog FM carrier these days as well (search aprs.fi for such stations near you).
What is an APRS host?
It is usually best to choose a server closest to your own location but sometimes there are located in other areas that you may find useful as well.
Telling your APRS software which of these hosts it should use comes down to choosing proper settings or entering call sign(s) into the appropriate field (most applications will allow copying&pasting from the list mentioned above).
Keep in mind that most hosts offer access via web browser without requiring any additional configuration by their visitors which might not always be good idea (e.g.: many stations share passwords with their "friends" easily or even make them public) so you might want to use hosts that require registration instead.
APRS-IS is an internet backbone for ham radio APRS data
The above map serves as a nice introduction but it doesn't show the whole picture and barely scratches the surface of what's out there thanks to efforts like APRS-IS which is basically a worldwide high speed network for sharing all sorts of digital modes (not only APRS).
Unfortunately, its main client software (called UIview) has been stuck in DOS era for ages and most modern operating systems such as Windows 7 (or even 8 & 10) won't run it at all without some serious tinkering with compatibility settings or virtual machine. There are other programs available these days however such as the above-mentioned APRS Messenger which is far more user friendly and easy to configure (also available for Windows, Android & iOS).
APRS Messenger doesn't require all the fiddling around with compatibility settings like UIview
Other clients like Xastir are still popular as well even though they may be slightly more difficult to set up or at least moving around within the software does. Most of them allow you to download current status of all network servers so you can see what's currently active in your area making it easier to find something nearby. Speaking of which...
Listening on APRS Frequencies
Besides using one of the map links mentioned earlier or dedicated hosts that list online stations by location, aprs.fi also has a list of all packet radio gateways in the world which might be easier to use if you already know what to look for however it's only updated once every few minutes.
It is usually faster to check status of network servers or dedicated hosts which are nearly realtime thanks to their web interface (or even digipeaters depending on your setup).
As I mentioned earlier, APRS is concentrated around 144.800 MHz so keep an eye out for anything nearby when trying packets out for the first time.
Due to its popularity and relatively rich feature set compared to traditional AX.25 packet radio, chances are that you will encounter multiple strong signals near this frequency since most modern mobile rigs support transmitting/receiving both at the same time (and often also on VHF simultaneously). If in doubt, simply ask for what's up when getting on the air and someone within range should be able to help out.
Talking is not always necessary but might speed things up
Most stations that are joining APRS network usually place themselves using just their call sign however due to its popularity when it comes to mobile traffic, expect most locals to use name & location instead (much like in case of D-STAR).
Allowing access only via plain callsigns would require manual configuration on each host so you can imagine how much work that would involve so in my opinion - if you hear an interesting conversation over APRS, don't hesitate to join even if they're already talking about something completely different at the moment. It's easy to ask for who's up by just mentioning *aprs # call* where # indicates the channel number (e.g.: *aprs 3*).
Just like in case of D-STAR, chances are that you will encounter voice conversations among APRS users especially if they're using mobile setups so feel free to join them and see what's happening.
Although it is usually okay to talk at any time, you might not want to interrupt someone doing an important exchange which should become apparent once you start listening or even better - ask first.
Once initial contact has been established, don't be shy about talking as well despite the fact that many stations are running mobile with poor antennas thus low signal levels, unless they're trying to decode a packet while you're already talking at the same time.
Transmitting APRS Packets
When it comes to forwarding your own position, APRS users tend to use either plain callsigns or name/location instead of creating their own transmission objects which saves them from editing hosts each day.
As I mentioned earlier - having access only via callsign might seem like a good idea at first however it's easily circumvented by simply using a commercial software that can create any object over the air and also allows configuration of custom object names (e.g.: *aprs #12345#).
Luckily, there are other options available besides sending your position as an object ripe for spoofing 🙂 . All modern hotspots such as DVRPTR, AirNav & WiMo allow for sending your position/call sign as a separate APRS message instead.
For example, you can easily send yourself a simple text-only message containing your call sign and current coordinates by simply entering *aprs #12345* (where # is channel number) in your default APRS messaging application such as UIview or APRSpoint which will automatically be converted to an appropriate object by any nearby hotspots.
Getting access to one of those requires either using a commercial hotspot solution such as DVRPTR's Voyager or more economic software alternatives such as AirNav , previously known as NaviTrack. In case of WiMo - it features the most powerful directional antenna I've seen so far making it an excellent choice for staying in touch on several different channels at once.
An interesting alternative usually used only by locals are digipeaters set up with path *WIDE2-1*, also known as RACES reflectors which can be easily reached by anyone even if they're not participating in the local emergency net.
One of those is APRS-ALY located on top of Kyiv National University of Construction & Architecture (KPI) that covers most of the city both vertically and horizontally 🙂 .
On average, you should be able to get access to each of them over one hop while DVRPTR's Voyager will automatically repeat anything sent to any WIDE2-1 digi within its range even if it doesnt
Does APRS Require a Tone?
So far, I've been mentioning AMTOR-A which is an obsolete protocol that requires either a separate terminal node controller (TNC) plugged into your computer or used as part of the modem itself.
While most TNCs these days are USB based, some more expensive models featuring proper hardware encoders/decoders are still available however this mode of operation was quickly replaced by AX.25 packet networks running on VHF & UHF frequences thus bringing us to the question - does APRS require a tone?
The answer is no - it doesn't! Since both D-STAR and APRS use FM transmission over commercial frequencies, you can think of them both as wideband modes making them incompatible with older narrowband protocols such as AMTOR.
Although it does make APRS accessible to anyone using a standard handheld such as the excellent Yaesu FT-7800R, newer radios such as TYT MD-390 come with integrated packet support making them better candidates for APRS use.
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However, just like with AMTOR - some software might require you to set up a separate TNC and configure its parameters before enabling APRS over RF.
This usually means settings such as data speed, packets timeout and delay between retries on either side of the connection so keep your eyes open if you're planning on doing something more than casual messaging or even chatting 🙂 .
APRS Software & Hardware
Although amateur radio licensing is apparently becoming more complicated lately compared to my impression of it in the past, still most software nowadays is available for free and there are lots to choose from. After using only UIview for several years, I recently got hooked on APRSpoint due to its excellent user interface especially when paired with a touch screen/resistive monitor.
Despite not requiring an internet connection or any other services running on your pc except WinPcap - GPS tracking works just fine even under Windows 7 so feel free to use whatever you're more comfortable with 🙂 .
When it comes to hardware - every radio should be able to run APRS out of the box regardless if it's VHF or UHF model while higher-end handhelds such as Yaesu's VX-8R also come with built in TNC.
For full desktop support - assuming you already have a sound card connected to your radio, any TAPR-compatible USB or serial port TNC should be sufficient together with an appropriate cable/software combination.
- The differences of UHF & VHF are explained here.
Let me also mention that for basic APRS operation you can use either VOX or keyboard PTT which is much more suitable in case of having to do something else while messaging other stations at the same time 🙂 .
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What is APRS Passcode?
In the world of APRS, a passcode is a number printed next to a repeating station's callsign meaning it has been verified by someone already. Since this doesn't apply to any other type of messaging or location services - make sure you understand what this means before coming up with your own custom one where somebody might intercept your messages!
As for standard passcodes - unless you're using well-known software such as UIview which makes it unnecessary, any serious packet radio operation should come prepared with at least four letter/number passcodes that have been previously agreed upon in the local net.
APRS Messenger & IGate A somewhat lesser known feature of APRS is the ability to send text messages over RF without a direct digipeater path using the concept of an IGate. This allows for example your local IT department or ham club to send their members location & status updates even when they're out of radio range and it's also a great way to keep up with what's happening in remote areas where digipeating might not be available.
Communication over APRS is usually limited by the distance the signal can travel line-of-sight since it doesn't use any repeaters/reflectors unlike D-STAR therefore there's pretty much no chance you'll ever see anything but short text messages unless you live close to a major city.
When compared to packet networks such as Winlink, APRS is still very small and mostly for passing traffic between local users however it could also be used for major emergencies or natural disasters when everything else goes down.
Taking APRS mobile One of the most important things about APRS is that it can work anywhere provided you have a GPS device running in your handheld, car computer or even smart phone because this allows users to send their own messages pointing to any location known by the system.
Imagine uploading your position including an attached message every few minutes into the network's database - then next time you get back home from another trip with a laptop and floor standing beam antenna connected to your radio, you'll be able to see both current & past messages from people passing by 🙂 .
What Are APRS Codes?
APRS is a popular local wireless protocol that uses 123 different codes to mark your current location and relay it to nearby users. These could be either automatically attached by APRS Messenger software based on the contents of the message you're sending or pre-defined manually before transmitting anything.
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