What is APRS

Automatic Packet Reporting System (APRS) is an amateur radio-based system for real time digital communications of information of immediate value in the local area.[1] Data can include object Global Positioning System (GPS) coordinates, weather station telemetry, text messages, announcements, queries, and other telemetry. APRS data can be displayed on a map, which can show stations, objects, tracks of moving objects, weather stations, search and rescue data, and direction finding data.

Although APRS needs internet for you to be able to see farther stations. It can work as a standalone RF digipeater, meaning, you can still send and receive data(messages) even when there is no internet! The more digipeaters, the more stations can use the services (just like cellsites).

Here’s a brief guide from aprs.fi

What equipment can I use?

APRS is operated in a rather simple to complex setup. Starting from radios that already have built-in APRS. Examples are Yaesu FTM-100 and FTM-400, portable radios like the FT1DR and FT2DR. Please see the radio’s manual for instructions on how to enable the APRS modem and setup beacons and messages, yes messages!

Moving forward, I will show you how I built my APRS TNC or Digipeater and gateway and a radio. Before that, let me define the terms:

TNC or the Terminal node controller, is a device used by amateur radio operators to transmit and receive packet data using airwaves.

Digipeater or Digital repeaters, is either a hardware or software based digital repeated. Unlike the standard voice repeater that receives on one frequency and retransmits what it hears simultaneously on another frequency, the usual digipeater is a single frequency device. It receives a packet of data, stores it in internal memory and then a moment later retransmits it on the SAME frequency. (More info here.

Radio Basically any radio capable of transmitting and receiving radio signals. 2m or 70cm.

Computer or Laptop used for monitoring other digipeaters and TNCs.

Trivia: Did you know that SMS or Text messages can be sent through APRS using your DMR Radio?

My APRS Digipeater station (4I1AYZ-10, 4I1AYZ-12)

My APRS setup is a software base TNC but I used an ICOM radio as transceiver for my TNC.


  • Raspberry Pi 3B+
  • External soundcard (Will use this since Raspberry does not have mic input)
  • Radio to PC interface
  • Icom IC-T7D
  • PC/Laptop
  • Direwolf for Linux (Debian)
  • APRSIS32 (Windows APRS Software monitoring)
  • UISS (Satellite APRS)

Brief How to:

  1. I have installed Raspbian Buster version for my Raspberry Pi OS. You can either use the desktop version or the lite version but due to my excitement I installed the desktop version which I would not recommend as it will take some space on the disk.

2. Radio to PC interface, here the picture of the interface, it’s the same interface used for simple repeaters and echolink stations as well. Since I have configured Direwolf to trigger GPIO 26 for PTT, I have to wire the PTT to Pin 37 of Raspberry Pi 3B+ (Please ignore incorrect pin in the wiring below).

3. ICOM IC-T7D, using the standard Icom speaker/mic cord, I cut off the end and soldered it directly to the Radio-to-PC interface using below diagram:

Note: I omitted the 10uF capacitor since the interface I used already has a 0.1uF capacitor built in.

4. You can now turn on your Radio. There is a group in Facebook, APRS Philippines, were hams share knowledge and experiences with APRS. A good start for beginners. Although still not official, 144.100 Mhz Is the APRS frequency for Philippines for now.

5. Off to software installation, install Direwolf, just follow the instructions in this site. Configuration is also indicated in the instructions. After running Direwolf, you should be able to get the below status.

6. Now that we have a working digipeater, we need to monitor the stations, messages, etc. so install APRSIS32 and you should be able to see the stations now:

7. APRS can also be used to send and receive packets from Satellites, although I have not been able to do so because of restrictions of building antenna in my location, some HAMs have done it successfully. You can use UISS in that case:

You can either use ISS Detector or Heavens above to track satellites like the NO-44 or PSAT-1 and even the ISS. You can see the status here for ISS APRS and here for all other APRS satellites.

So there you are, no internet, no problem, you can still send text messages through APRS. Oh! I remember, the TRIVIA!

“Did you know you can send text messages through APRS using your DMR Radio?”

Here’s how:

1. Login to Brandmeister network and go to SelfCare.

2. Select the brand of your radio, make sure to select only Motorola or Hytera as others will not work.

3. Enter your APRS Callsign, make sure it has a suffix –(1), like 4I1AYZ-1.

4. Save the settings.

5. To send SMS to another HAM enter the aprs callsign of the HAM you wanted to contact then space and your message. Then send it to 515999 (Philippines). That’s it and enjoy! 73

Compose message

Send to 515999 or the country code of BM followed by 999

Confirmed message received!

Pi-Star Status


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