APRS for Beginners

This document was first created on Feb 21, 2021.  It was last updated on April 3, 2024 to reflect the demise of SMSGTE, the emergence of SMS, and to change a bit of wording here and there.  This is a brief primer on APRS for those interested in using that technology.  This is very much an end-user document, not an infrastructure-side document.  It is aimed at those who wish to use the system for their own purposes, usually emergency communications.

APRS stands for Automatic Packet Reporting System.  It is a system that allows the passing of digital information over amateur radio in real-time.  APRS is dependent on radios and iGates that have been designed to encode and decode AX.25 formatted packets.  Using APRS, you will be able to:

• Send text-only emails to any valid email address

• Send SMS text-only messages to any North American cellular phone

• Send beacons of your position (and other information) which will be displayed on various Internet front-ends like aprs.fi 

• Send direct messages to other APRS enabled radios in your area

• Review (on the front-ends mentioned above) APRS traffic and beacons for any area worldwide.

To use APRS, you will need one of the following.  More specifically, either of the first two (the radio and the smartphone app) can do APRS alone.  The third (a compatible TNC) needs a radio and a front end like an Android app to be useful.   Generally speaking, the radio-based solutions will require you to set your frequency to 144.390 in order to function in North America, although there are regional exceptions and one should check what the frequency is for each local area.  These other frequencies are listed further down in this document.

The best known feature of APRS is position reporting (commonly called beaconing).  This is a feature of APRS enabled radios to send the GPS position of the radio along with some other basic information (like your call sign and a beacon message) to APRS-IS where it is then displayed on APRS front-ends like aprs.fi and aprs-map.info.  Generally speaking, beaconing is simply a matter of changing the settings your APRS device to enable it.  On a Yaesu FT3D, for instance, one simply needs to set the APRS Modem to "on" and the Beacon Tx to Auto.  It is important to note that beaconing generally doesn't work on most radios unless the radio has a GPS fix.

Sending emails with APRS is simple.   One simply composes an APRS message like any other, with the recipient set to either EMAIL or EMAIL-2.  These are both  javAPRSSrvr Email Gateways and are set to relay messages to the internet.   The first part of the message must be the email address you are trying to send to, followed by a space, and then the contents of your message.  

For example:

To: EMAIL

Message: reg@testdomain.ca test message

This would result in an email being sent to reg@testdomain.ca with the contents "test message".  Keep in mind that there is no way to send binaries such as photos via APRS email.  You should see a confirmation similar to "Email sent to reg@testdomain.ca".

Sadly, the SMSGTE service which used to allow us to send texts to any phone number is now defunct due to both spam and changes in law.  There is a new SMS service available, but it requires an explicit opt-in by the recipient which makes it far less useful.  To use that service, simply  send a message from APRS to SMS using the following format: @<number> <message>  

For example:

To: SMS
Message: @9876543210 No cell coverage. Get me on the radio! 

The recipient would receive: @NA7Q-3 No cell coverage. Get me on the radio!

To opt in, have your recipients visit this site.  

NOTE: As of April 3, 2024, text messages appear to be going through using the SMS service regardless of whether the number has been registered or not.  I have just done several tests and all have worked without the number being registered.  I do not know if this is by design or if it is a temporary situation.  Right now, however, it seems to work without registering.

Sending direct messages with APRS is the simplest of all the messaging options in APRS.   One simply composes an APRS message with the recipient set to the call sign of the APRS device one wishes to send the message to.  The APRS system handles the rest.  It is important to include the SSID of the device.  The SSID is simply a numeric identifier that follows your call sign with a hyphen.  Every call sign can be followed by an SSID, and most APSR users assign different SSIDs for each of their APRS devices.  My call sign is VA7ZEB and my handheld is VA7ZEB-7 and my car is VA7ZEB-9 and so on.

For example:

To: VA7ZEB-7

Message: test message

This would result in a "test message" being sent to my handheld.  Unfortunately there is no guarantee of confirmation from the APRS direct message system your message has been sent.  You might get one if the relaying iGate is bidirectional, or you may not if it is receive-only.

The most common reason for problems with the APRS messaging system is that the user is not within range of any iGates.  A good way to see if you are in range of any iGates is simply to go to aprs.fi or aprsdirect.com and look for nearby iGates.  These are usually marked with a black R or D, or a green S or I.  If there are none in your area, consider setting up an iGate using the instructions here.

144.390 is the most common APRS frequency worldwide, but one should be aware of the various frequencies in use around the world.

• 144.390 MHz – North America, Colombia, Chile, Indonesia, Malaysia, Thailand

• 144.575 MHz – New Zealand

• 144.660 MHz – Japan

• 144.800 MHz – South Africa, Europe, Russia

• 144.930 MHz – Argentina, Uruguay

• 144.990 MHz – Vancouver, Canada (Handhelds only)

• 145.175 MHz – Australia

• 145.570 MHz – Brazil

• 145.825 MHz - ISS (International Space Station) 

• 432.500 MHz - IARU R1

In the Vancouver (Canada) area, a group of local hams found that the common APRS frequency of 144.390 was congested with mobile traffic so a series of iGates was set up on 144.990.  These are intended generally for handheld use, with the goal of leaving some iGates free of more powerful mobile traffic.  If you are in the Vancouver area and are having trouble reaching the various .390 iGates with your HT, it's worth trying .990.  I'm told this is true for some other areas, too.

D-PRS is the Icom version of APRS and DMR-APRS is the DMR version.  Both are digital standards that require specialized repeaters/iGates that are configured to work on those systems.  Obviously in the case of D-PRS, an Icom D-Star repeater/iGate is required and with DMR-APRS, a DMR repeater/iGate is required.  D-PRS radios and DMR-APRS radios are generally not able to use standard APRS iGates.  These two digital standards have not achieved widespread adoption and should only be considered if the user is certain that such repeaters/iGates are available in the user's area of use.  In general, standard analog APRS repeaters/iGates are far more common and readily available than repeaters/iGates using these digital standards.  Even if one does have good digital coverage in their area, they should keep in mind that such coverage will likely not exist in all places the user might travel to.

I hope this brief APRS primer has been useful to you. 

73,

Reg Natarajan

VA7ZEB / HJ1ZEB