Tagged: automatic packet reporting system

A Pre-Built Raspberry Pi Image for using an RTL-SDR as an APRS RX iGate

Keith Maton (G6NHU) wrote in and wanted to share his new ready to go APRS RX iGate image for the Raspberry Pi. APRS stands for “Amateur Packet Reporting System”, and is a type of packet radio communications system used by Amateur Radio operators. They often use them to transmit short mail messages, weather sensor updates, track vehicles and for various other purposes. An iGate allows APRS messages to be transmitted over the all world via the internet via a signal chain such as: RF->iGate RX->Internet->iGate TX->RF.  To run an iGate you should be a radio amateur with a callsign. A global aggregation of APRS broadcasts received by iGates can be seen at aprs.fi.

An RTL-SDR can be used to receive APRS packets easily and many amateur radio enthusiasts have been setting up APRS RX only iGates using the “direwolf” decoding software. Keith’s image simplifies the process of installing and configuring software significantly by proving a plug and play image that you just burn to an SDcard and plug into your Raspberry Pi. His post also explains how to configure the iGate correctly.

iGate Raspberry Pi Image Running
iGate Raspberry Pi Image Running

Solving APRS Interference Issues with a Bandpass Filter and Coax Notches

John, DK9JC N1JJC wanted to set up an RTL-SDR APRS packet iGate. APRS stands for “Amateur Packet Reporting System”, and is a type of packet radio communications system used by Amateur Radio operators. They often use them to transmit short messages, weather sensor updates, and for vehicle tracking. An iGate allows APRS messages to be transmitted over the all world via the internet like so RF->iGate RX->Internet->iGate TX->RF.

When trying to receive the APRS packets John discovered a problem. He discovered that there was a very strong 100kW broadcast FM and 50kW DAB transmitter on a transmission tower in line of sight of his antenna. The strong signals were overloading the dongle and completely wiping out the APRS packets that he was trying to receive at 144.8 MHz.

First John tried a simple bandpass filter with 0.8 dB insertion loss and 20dB attenuation. The filter still wasn’t enough, so he went and made a several coax notch filters to take out each of the interfering signals. A coax notch filter is simply a length of coax connected via a “T” junction to the main coax cable. This creates a notch of attenuation at a frequency depending on the length of the notching coax. With these notches combined with the bandpass filter he was finally able to receive APRS packets.

A coax notch filter
A coax notch filter

Setting up a Raspberry Pi based APRS RX IGate with an RTL-SDR

Recently amateur radio hobbyist WB20SZ wrote in to us to let us know about his work with creating an easy to build receive only APRS internet gateway (IGate) with a Raspberry Pi and RTL-SDR dongle. The process involves using WB20SZ’s “Dire Wolf” software which is a free Linux based APRS encoder/decoder. He writes that it can be used to observe APRS traffic, as a digipeater, APRStt gateway or Internet Gateway (IGate). Setting up the APRS IGate is a simple matter of piping the received APRS audio from rtl_fm into the direwolf software. Instructions for installing direwolf can be found here.

APRS stands for Automatic Packet Reporting System and is a packet radio protocol used by radio amateurs to broadcast real time data such as messages, announcements, weather station reports and sometimes the location of vehicles. If an APRS station has a GPS attached to it, the broadcasts will also contain the GPS coordinates. Internet Gateways or IGates are repeaters that are used to receive messages from a local radio and pass them on via the internet to a transmit capable IGate repeater anywhere in the world. To run an IGate you should be a radio amateur with a callsign. A global aggregation of APRS broadcasts received by IGates can be seen at aprs.fi.

Various APRS messages seen on aprs.fi
Various APRS messages seen on aprs.fi

Using Xastir with the RTL-SDR

Xastir is a Linux based program that is used for plotting Automatic Packet Reporting System (APRS) data on a map. APRS is is type of packet radio system used by ham radio for real time local area digital communications. It is often used for sending messages, plotting positions on a map or providing weather station data.

Over on his blog, KJ6VVZ’s has uploaded a post showing how he was able to get the RTL-SDR working with Xastir. He uses rtl_fm piped into MultimonNG for the APRS decoding and then sends the decoded APRS information to Xastir via a FIFO buffer.

Xastir Message Log
Xastir Message Log

Decoding APRS with SDR#, APRSISCE32 and an RTL-SDR

Over on YouTube user k2nccvids has posted a video showing how he was able to decode APRS signals and plot them on a map using APRSISCE32. APRSISCE32 is an advanced Automatic Packet Reporting System (APRS) decoder which has mapping capabilities and can also connect to the internet as an iGate. APRS is used by amateur radio hobbyists to send data like messages, announcements and also GPS coordinates.

http://www.youtube.com/watch?v=oHCTgKc8VL4