APRS with an RTL-SDR – Part1

Recently I purchased a RTL-SDR to play with. These are dirt cheap on Amazon or Ebay usually to the tune of $10 or less shipped to your door. I had a few different ideas of how I would use this, but first on my list was to build an APRS receiver & decoder.

First I had to figure out how to get my RTL-SDR working on Linux. First we need to install a bunch of pre-requisite packages on our Debian/Ubuntu system.

# sudo apt-get install doxygen doxygen-gui doxygen-latex doxygen-dbg doxygen-doc gnuradio-dev gnuradio libgnuradio* libboost-all-dev libusb-1.0-0-dev libusb-1.0-0 gnuradio build-essential cmake mono-complete monodevelop libportaudio2 fftw3-dev

Next we need to download and install the rtl-sdr drivers. Please follow This Link for more information.

After installing the drivers, we need to patch gnu-radio. Please follow This Link for more information.

Next we need to blacklist the standard dvb_usb_rtl28xxu kernel module. Run the following command:

# sudo echo "blacklist dvb_usb_rtl28xxu" >> /etc/modprobe.d/blacklist.conf

Next we need to install kalibrate. Kalibrate is a tool used to calibrate the RTL-SDR using GSM towers in the 900mhz band.

# git clone https://github.com/steve-m/kalibrate-rtl cd kalibrate-rtl
# ./bootstrap && CXXFLAGS='-W -Wall -O3'
# ./configure
# make
# sudo make install

Finally, I installed SDR # which isn’t technically necessary for APRS decoding, but it is a fun way to play with the RTL-SDR that doesn’t requiring doing a lot of hacking in Gnu-Radio.

I’m going to wrap up Part 1 here. This should get you to a working state with your RTL-SDR. In Part 2 I’ll go into getting the Ham Radio side of the software configured.

That’s all for now.

73!

APRS – Ham Radio and Mapping

APRS – Ham Radio Special Modes:

One of the great strengths of Amateur Radio is how flexible the hobby is. One type of operation that is very interesting for the Overlander is called APRS. (Amateur Position Reporting System) APRS takes raw NEMA2 data from a GPS, encodes it, and transmits it over the amateur bands. A simple APRS Transmitter/Receiver can be built by connecting an inexpensive handheld transceiver (around $35 on Amazon) to an Android Phone or Tablet with a GPS, and then installing a $4.95 piece of software called APRSdroid. This APRS site can then simultaneously transmit your coordinates, as well as display the near real-time locations of every other APRS station within receiving distance. Imagine a caravan of five vehicles, each with an small APRSdroid powered APRS system in their vehicles, with the map display turned on.

Android Phone, and Baofeng UV-3R
APRS Portable

Map Display
Map Display

Overland Mapping & Ham Radio

It’s no big secret I have a bunch of radios in my truck. In fact one of my next posts will highlight what I have installed in my Mobile Antenna Farm.

Mobile Antenna Farm

One of the radios installed though is a 10w Byonics Microtrak-RTG APRS Transmitter. If you’re not familiar with APRS take a second to read a little about it.

While driving through the mountains on the Rimrocker Trail my APRS transmitter was happily sending out telemetry data every 5 minutes (because I was traveling less than 60 miles per hour) or every time I had a more than a 14 degree change in direction. Because of the range 2m has while in the mountains (Line of sight from 9,000 feet is a long way.) I actually have a pretty complete picture of where we traveled.

RimRocker APRS Tracks

APRS isn’t as perfect as plotting your own maps with an onboard GPS and Tracking software, but it’s kind of neat to know that the family of one of the guys with us could fairly reliably track our progress through the Rocky Mountains.