Listening to TETRA Radio

Use your RTL-SDR in Linux to listen to TETRA, a digital trunked radio communications system that stands for “Terrestrial Trunked Radio”.

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Analyzing GSM with Airprobe/GR-GSM and Wireshark

The RTL-SDR software defined radio can be used to analyze cellular phone GSM signals, using Linux based tools GR-GSM (or Airprobe) and Wireshark.

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Receiving Meteor-M N2 LRPT Weather Satellite Images

The Meteor-M N2 is a polar orbiting Russian weather satellite. With an RTL-SDR an appropriate antenna, you can receive and decode its image downlink and download LRPT weather satellite images.

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Roundup of Software Defined Radios

New software defined radio (SDR) products are popping up every few months these days so we thought we’d compile a big list of available SDRs.

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Receiving ACARS Airplane Data

ACARS is an acronym for Aircraft Communications Addressing and Reporting System and is a digital communications system that aircraft use to send and receive short messages to and from ground stations. With an RTL-SDR these messages can be decoded.

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JAERO: A RTL-SDR compatible decoder for Inmarsat AERO signals

AERO is a system that provides a L-Band satellite based version of VHF ACARS (Aircraft Communications Addressing and Reporting System). ACARS is typically used by ground control and pilots to send short messages and is also sometimes used for telemetry. With JAERO and an RTL-SDR these signals can be decoded.

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List of SDRSharp Plugins

There are a number of SDRSharp plugins that extend its functionality. Here is a collection of all the plugins and download links that we know of.

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RTL-SDR Direct Sampling Mode

The RTL-SDR software defined radio can be told to run in a mode called “direct sampling mode”, which with a small hardware mod allows the dongle to tune to the HF frequencies where ham radio and many other interesting signals are found. This means that no upconverter circuit is required.

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Receiving Weather Balloon (Radiosonde) Data with RTL-SDR

Use your RTL-SDR to decode data from weather balloons (aka Radiosondes) that are launched twice daily by meteorological agencies all around the world.

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Cheap ADS-B Aircraft RADAR

Modern planes use something called an ADS-B (Automatic Dependent Surveillance-Broadcast) Mode-S transponder, which periodically broadcasts location and altitude information to air traffic controllers. The RTL-SDR can be used to listen to these ADS-B signals, which can then be used to create your very own home aircraft radar system.

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RTL-SDR Tutorial: Decoding DRM Radio

Digital Radio Monodial (DRM) radio is a type of digital shortwave radio signal that is used by international shortwave radio broadcasters. It provides superior audio quality compared to AM signals by using digital audio encoding. With an upconverter, good antenna, and decoding software the RTL-SDR software defined radio can receive and decode DRM signals. This tutorial is also applicable to other software defined radios that can receive HF with or without an upconverter, such as the HackRF, Airspy, Softrock and Funcube dongle.

Examples of DRM Decoding

YouTube user Superphish shows DRM reception with his Ham-it-up upconverter, and rtl-sdr. http://www.youtube.com/watch?v=xuLqpJvE0d0 YouTube user vu2ufg shows another example of DRM reception with the RTL-SDR. http://www.youtube.com/watch?v=25ZYSjhEP2o

Tutorial: How to Receive and Decode DRM Signals

To receive DRM with RTL-SDR, you will need the following:

  1. An RTL-SDR dongle working with SDRSharp. (Or a more advanced SDR such an Airspy)
  2. An HF upconverter such as the recommended SpyVerter or ham-it-up, or a dongle modded for direct sampling, or SDR# modded to use the experimental Oliver Jowett HF driver.
  3. The DREAM DRM decoding software with AAC decoder.
  4. Virtual Audio Cable or VB-Cable.
DRM Signal Example
Left: DRM Signal, Right: Analogue AM Signal

We will assume you have a rtl-sdr dongle with HF upconverter, and have set it up with SDRSharp and an audio piping utility such as Virtual Audio Cable or VB-Cable which allows the audio to be passed from SDRSharp to the decoding software. If you have not set these up, check out the Buy RTL-SDR and Quickstart pages, and head to the virtual audio cable download page (trial), or the VB-Cable download page (free). The sampling rate of your audio piping method must be set to 48000 samples/sec. To set this in Windows, right click your device in the Windows sound recording tab, go to properties and under the advanced tab, set the sample rate to 48000 Hz. Do the same to the same device under the Playback tab as well. Sound Properties Now, head to the DREAM download page, download DREAM and extract the zip file into a folder. DREAM is a free opensource DRM decoder. Due to software licence reasons the required audio decoder can not be shipped with the DREAM binary file. You can follow the instructions on the download page to compile your own faad2_drm.dll decoder, but as not everyone has compilation experience, a precompiled faad2_drm.dll download for windows can be found at this megaupload link. Note that using this file in some countries may not be legal due to patent laws. Place the faad2_drm.dll file into your DREAM folder. Now you can open SDRSharp, set virtual audio cable as the output audio device, and then tune to a DRM signal. DRM signals use upper side band (USB), and have a bandwidth of 10 kHz, so apply these settings to SDRSharp as well. Carefully align the left red line with the start of the signal. AGC can be left on, but it may need to be experimented with in order to get the best decoding performance. You should also experiment with the filter order. I have usually found a large filter order of 100+ to work well as this helps to remove noise from nearby interfering signals. A DRM signal looks like this (left) on the waterfall, placed next to a normal shortwave AM signal (right). Now, open DREAM and then go to Settings -> Sound Card -> Signal Input -> Device and set Virtual Audio Cable or VB-Cable as the input device. Also, ensure that Settings -> Sound Card -> Signal Input -> Sample Rate is set to 48000 Hz. DREAM Audio Settings Try to get the green “Level [dB]” bar in DREAM to be near the center by adjusting the volume settings in SDRSharp. If everything is set up correctly, you should see three green bars underneath the volume meter and start seeing information about the DRM radio station you are tuned to in the window, and also begin to hear some audio. DREAM

Some Tips:

  • To receive DRM signals you will need a good HF antenna, placed up high. A simple long wire strung across your attic may work well. Look up “random wire antenna”. Also a magnetic loop antenna may be a good choice.
  • RTL-SDR tends to place imaged broadcast AM signals into some DRM signals. This can cause decoding to completely fail. We suggest trying a HF filter that blocks the AM broadcast band.
  • If you hear no audio when decoding, check that you have placed faad2_drm.dll into the DREAM folder correctly.
  • DRM is a digital signal, so it will either work and play audio or it will not work at all. Poor reception may cause the audio to constantly drop out.
If you enjoyed this tutorial you may like our ebook available on Amazon.

The Hobbyist’s Guide to the RTL-SDR: Really Cheap Software Defined radio.

8 comments

  1. Megaletdown

    that creepy megaupload link is probably outdated and they won”t let me in with my browser. how insane is it that i normal non computer savvy people are supposed to compile a program to get some freeware running??

  2. Pingback: Rtl-sdr | Pearltrees
  3. Dean

    You do NOT want to use that Megaupload site. It will attempt to put about 50 MB of crap on your computer if you consent to the download.

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