APRS RX - portapack-mayhem/mayhem-firmware GitHub Wiki

Automatic Packet Reporting System

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The APRS RX app receives and displays messages transmitted using the APRS (Automatic Packet Reporting System) protocol. It shows a live list of received stations including callsign, position (if available), hit count, and last received time.

Pre-configured Regions

Select a region to automatically tune to the correct APRS frequency for that area:

Code Frequency Region
MAN user-defined Manual — frequency set manually
NA 144.390 MHz North America
NZ 144.575 MHz New Zealand
JAP 144.640 MHz Japan
PHI 144.740 MHz Philippines
EUR 144.800 MHz Europe / UK
THA 144.900 MHz Thailand
AUS 145.175 MHz Australia
BR 145.570 MHz Brazil
ISS 145.825 MHz International Space Station

When a region is selected, the frequency field updates automatically. If you change the frequency manually afterwards, the region selector switches to MAN.

Controls

Frequency

  • Use the rotary encoder over the frequency field to adjust in steps
  • Press the middle button over the frequency field to enter a frequency manually via keypad
  • Load a frequency from SD card using the frequency manager

Radio Settings

From left to right:

  • AMP — RF amplifier: 0 = off, 1 = on (+14 dB). Enable if signal is weak.
  • LNA — IF gain (0–40 dB in 8 dB steps)
  • VGA — Baseband gain (0–62 dB in 2 dB steps)

See Description of gain settings for more details.

Volume

Audio volume is shown after the signal strength bars. Use the rotary encoder when focused on it.

Station List

The main screen shows a list of recently received APRS stations with the following columns:

Column Description
Source Callsign of the transmitting station (with SSID if present)
Location GPS coordinates if the packet contained a position report
Hits Number of times this station has been received
Time Time of last received packet

Tap or select an entry to open the Detail View.

Detail View

Selecting a station from the list opens a detail screen showing the full decoded APRS packet information including the raw info field content. Two buttons are available:

  • Done — return to the station list
  • See Map — opens the map view centered on the station's position. This button is only visible if the station transmitted a valid GPS position.

Logging

Received packets are automatically logged to the SD card at:

LOGS/APRS.TXT

Each line contains the raw decoded APRS stream data. Logging is active as long as the app is running and a writable SD card is present.

Important Notes

  • APRS RX on the HackRF is relatively insensitive. Enable AMP if you are not receiving stations that are clearly audible on a dedicated receiver.

⚠️ Be careful not to connect strong signals directly — the HackRF has no input protection.

  • Some stations transmit with a bandwidth wider than the default 8.5 kHz. If you are missing packets, increase the reception bandwidth by editing the settings file on the SD card:
    1. Navigate to SETTINGS/rx_aprs.ini using the File Manager app
    2. Select the file, press down to select the pen icon, press OK
    3. Find the line starting with nbfm_config_index and change the value:
      • 0 = 8.5 kHz (default)
      • 1 = 11 kHz
      • 2 = 16 kHz

Further Reading