APRS

You may have read or heard the term APRS.  This four letter acronym isn’t self-explanatory but is popular and important enough that we should cover the basics.

Do you need APRS? Unlikely.  Do you want it? Maybe.   Planning to buy a new VHF/UHF radio and wonder if this is a feature worth paying for?  Read on.  APRS is a big topic with way more detail than we can present here so we’ll give you a general idea of what it involves along with some research links to answer these questions yourself.

For starters, APRS stands for Automatic Packet Reporting System.

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Some publications mistakenly call it Automatic Position Reporting System

Refer to our packet topic for a background on what packet radio is all about.  What makes APRS a specialized form of packet is what info is transmitted.

APRS supports four data types, including Position/objects, Status, Messages and Queries.  The position packets contain latitude and longitude, a symbol to be displayed on a map, plus optional fields for altitude, course, speed, radiated power, antenna height above average terrain, antenna gain, and voice operating frequency.

While APRS can send packets over greater distances on HF bands, it is more commonly used with VHF FM (2m) radios to share data of interest in the local area such as GPS coordinates, weather, alerts, announcements, and such.

APRS info and messages can be directly between hams but more commonly, packet data is collected by local repeaters (gateways) and sent to the APRS Internet System (APRS-IS) for retrieval anywhere by anybody with a web browser.  Meaning your unlicensed spouse can see where you are located (technically, your transceiver) at any given time.  It is not a one-way system; APRS both transmits and receives packet data.

Also unlike normal packet radio, APRS blindly sends out data addressed to no one in particular (unconnected). Two things to know about this system: 1) no error correction (clean, strong signals required), 2) someone or something must be monitoring to be useful (another APRS ham or internet gateway).

In addition to several good references below, an excellent resource worth reading right now: Intro to APRS (PDF file link), a presentation prepared by John Gorkos AB0OO of the Joplin (MO) ARC.   It discusses what the system is not, significant info you can get through it, what you can do with it (note two separate sections for this), and suggests next steps for getting involved with APRS.

Given all the possibilities above, the primary use of APRS in ham radio is to have a transmitter location reported to a central database periodically so that others can see where a mobile/portable ham is located.

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This makes APRS particularly useful for public service events and emergency communication (EmComm) situations where managers can easily track mobile resources who have messaging capabilities.

There are numerous web services for viewing APRS maps and data but the main one (and simplest) is  aprs.fi .  Click there and you will be taken to a local map showing locations of ham APRS transmitters in your own area.  Looks like this example:

APRS Map

In North America all APRS data is transmitted on 144.390 MHz.

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Just tune your VHF radio to your global frequency to hear the packet squeal, if you are wondering what it sounds like.

APRS requires not only a 2m FM transceiver but also a computer with display and TNC radio-computer interface, plus (normally) a GPS receiver.  Radios with APRS features built in cost more than ordinary mobile or handheld transceivers, mainly because Continue reading

Packet Radio

If you’re exposed to ham radio for any length of time you are sure to hear some discussion of packet radio.

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Without going into much detail, we’ll present a big-picture description here.  Just enough for you to have a basic grasp of what’s involved and give you some idea of how it might apply to you.

Packet radio is a generalized term for a digital communication mode where data is sent in bite-sized chunks (packets) via radio.  The transmission and receipt of packet data is largely automated and features data error correction for reliable messaging.

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Packet radio (sometimes shortened to just packet) blends radio and computer technologies together.  Sounds complicated but it really isn’t.  All you need besides your normal ham radio transceiver is a household computer and an interface between the two.  The heart of this interface is a Terminal Node Controller (TNC) which is an intelligent modem that converts text to audio tones and vice versa.

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Packet radio can be used between hams directly in real-time (peer-to-peer or keyboard-to-keyboard) but is more commonly used to send messages that can be retrieved on demand.  This operates more like email or mobile phone text messaging.

Slow data rates (typically 1200 baud) make large messages impractical, so packet messages should be relatively short and not have any large files attached.  120KB is the max message size accepted by some big message servers.  A 4KB message will transfer in 2-2.5 minutes under ideal conditions at 1200 baud.

Particularly useful for emergency communication (EmComm) messages, packet radio is predominately used on VHF radios (more local) but can be sent over HF bands Continue reading