March 2, 2015

Decoding Aviation VOR and ILS Signals with RTL-SDR

Previously we’ve posted about how hpux735 (aka William) was able to use an RTL-SDR to decode an aviation VOR navigation signal using GNU Radio and an RTL-SDR. VOR is an acronym for VHF Omni Directional Radio Range and is an older method of navigation used by aircraft.

Now over on YouTube William has uploaded a new video that continues his series on decoding VOR and navigation radio signals. This time he focuses on ILS or Instrument Landing System signals. The ILS is a radio system that is used to help aircraft find and land on the runway safely even in reduced visibility situations such as rain and fog. William’s video explains how ILS works and also shows how he is able to make use of the ILS signal in GNU Radio to extract navigation information.

William has also uploaded some supplemental material to his blog including the GNU Radio grc file and the baseband ILS signal data he collected whilst flying.

VORs and SDRs Part 3: ILS

Watch this video on YouTube

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February 25, 2015

Linux Command Line based Doppler Correction and Demodulation Tools

Programmer Andres has recently been working on creating a toolset for receiving AX.25 packets (FSK 9600) from satellites with an RTL-SDR or other software defined radio. The AX.25 protocol is commonly used for APRS packet radio or telemetry in amateur radio satellites. Andres’ programs focus on using a true UNIX philosophy of piping data between different programs. The toolset consists of doppler correction and demodulation tools and the piping philosophy is demonstrated in the following example:

rtl_sdr | doppler | demod | multimon-ng

Andres writes…

rtl_sdr receives raw IQ data from satellites which is then piped to “doppler” which corrects doppler offset. Zero centered baseband signal is piped to “demod” which outputs demodulated audio suitable for multimon-ng to do actual AX.25 packet decoding.

Such pipeline is intended for resource constrained embedded platforms like RaspberryPi or BeagleBoneBlack where running full blown SDR software would be too much.

The doppler corrector tool works by using the same libraries for calculating satellite positions as those used in Gpredict and the demod tool uses the liquid-dsp library to demodulate the IQ stream.

More information about Andres’ project can be found in these three blog posts that he has written.

Andres also writes that he would be interested in hearing any feedback or pull requests on GitHub for these tools.

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February 25, 2015

How to Receive the Funcube Satellite with an RTL-SDR

Over on the Hamspirit.de blog author Jan as written a post explaining how to receive the FUNcube satellite with an RTL-SDR dongle (note in German, use Google translate). The FUNcube is a CubeSat (a low cost miniature 10 cm cube sized satellite) which is intended mainly for educating young people about radio, space, physics and electronics, but has also piqued the interest of amateur radio hobbyists.

Jan first writes how the Funcube Dongle was originally invented as a low cost means of receiving the FUNcube satellite, but now there are the even lower cost RTL-SDR dongles. Jan’s post then goes over how to receive the FUNcube at a frequency of 145.935 MHz using software such as SDR-Radio or SDR# and how to decode the telemetry data using the FUNcube dashboard. He also explains a bit about the FUNcubes operating modes which change the satellites transmission strength depending whether or not its solar panels are in sunlight or not.

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February 23, 2015

ARTEMIS: Free Signal Identification Software

Marco, a reader of RTL-SDR.com and user of our sister site sigidwiki.com has been developing some Windows software to display the sigidwiki.com database in an easier to access format. The software is called Artemis and can be downloaded from http://markslab.tk/project-artemis/.

Artemis allows for various example signals to be quickly viewed with the corresponding example waterfall image, frequency, bandwidth and other information. There is also a filtering function that allows you to search by frequency and type of signal.

Marco writes that he would love to hear any user requests for new features such as more filters, improvements, or anything else as well as any bug reports. We also note that data such as frequencies and bandwidths provided in the sigidwiki.com database may not yet be 100% correct since the wiki is relatively new and is yet to mature.

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February 23, 2015

SDR Capture The Flag Competition Tutorial

During several hacker and security themed conferences (Shmoocon, Bsides, Derbycon, Defcon, etc) organizers from Wireless Village have been setting up competitive WiFi and SDR themed capture the flag (CTF) games. In the competition the organizers broadcast a signal and the competitors are required to complete various tasks (capturing flags) such as determining the centre frequency of the transmission, demodulating the signal and finding any meta data contained within the signal such as codec flags in DVB-T signals and RDS data in FM signals. The team which captures the most flags wins a prize. The process of capturing flags often requires the use of some sort of software defined radio like the RTL-SDR, HackRF or BladeRF.

Recently, Russell one of the CTF organizers wrote in to let us know about a SDR CTF training resource that he has put together. The site contains various exercises/tutorials that allow participants to practice the skills needed to compete in the competition. Most exercises involve using a Raspberry Pi together with PiFM for transmitting a simulated competition signal, then receiving and demodulating the signal with a SDR. The exercises include running rtl_power, setting the PPM offset, decoding morse code, AFSK, RDS, ASK/OOK, DVB-T, POCSAG, MotoTRBO, SSTV and decoding numbers stations.

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February 22, 2015

The International Space Station is Transmitting SSTV Images

Happysat, a reader of RTL-SDR.com has written in to remind us that the International Space Station (ISS) is currently transmitting slow scan television (SSTV) images out of respect of the 80th birthday of Russian cosmonaut and first man to go to space Yuri Gagarin. The images will be transmitted continuously until 24 February 21.30 UTC.

SSTV is a type of radio protocol that is used to transmit low resolution images over radio. A RTL-SDR dongle and satellite antenna (QFH, turnstile, even terrestrial antennas like random wire antennas and monopoles have been reported to work) can be used to receive and decode these images. Happysat writes that it is expected that the ISS will continuously transmit 12 images at a frequency of 145.800 MHz FM using the SSTV mode PD180, with 3 minute off periods between each image.

To decode the images it is recommended to use SDR# and pipe the audio into MMSSTV, a freeware SSTV decoding software program. To get the best results out of MMSSTV happysat recommends enabling “Auto slant” and “Auto resync” under Options->Setup MMSTV->RX.

To know when the ISS is overhead you can track it online using http://spotthestation.nasa.gov/sightings/, http://www.isstracker.com/ or http://www.mcc.rsa.ru/English/trassa.htm.

Received SSTV images can be submitted to the ARISS Gallery, and Happysat has also uploaded a collection of his own personal received images here.

Happysat also shows us some images from the ISS showing the Kenwood D710 transceiver located in the Russian service module, the computers used to generate the SSTV signal and the antennas used for amateur radio transmission.

One of the broadcast SSTV images from the ISS — One of the SSTV images broadcast from the ISS

Computers on the ISS used to transmit SSTV images

Antennas on the ISS used to transmit SSTV images

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February 20, 2015

Highlighting some SDRPlay Reviews

Update: Note that we also now have our own comprehensive review available here which compares the Airspy, SDRplay RSP and HackRF.

The Radio Spectrum Processor (RSP) by SDRplay is a receive only software defined radio with a 100 kHz to 2 GHz range (with a small gap at 380 MHz to 430 MHz), a 12-bit analogue to digital converter (ADC) (~10.4 ENOB), 8 MHz bandwidth and a bank of several switched front end filters. It currently costs $299 USD and with these specs and price range we consider the RSP to be a competitor to the Airpsy and Funcube Dongle software defined radio offerings.

Recently several reviews of the SDRplay RSP have been written online and in magazines. The first review comes from the pages of the UK based Radio User magazine (pdf warning) which goes through the specs, design, install and operation of the device. A more recent review shows an unboxing and there’s also this review submitted to the SDRplay team which demonstrates some FM dxing results. There are also several more reviews collected by the SDRplay team linked on the SDRplay website at http://www.sdrplay.com/reviews.htm.

We also note that we recently posted about some in depth measurements that Leif (programmer of Linrad) recently made to multiple SDR’s, including the SDRplay.

The Radio Spectrum Processor (RSP) by SDRplay.

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February 20, 2015

The SatNOGS Story

In a previous post we talked about the SatNOGS project which aims to provide low cost satellite ground stations (where one critical component is currently an RTL-SDR dongle) along with free networking software in order to create a crowd sourced satellite coverage network. The SatNOGS project was also recently the grand prize winner of the Hackaday prize which saw them take almost $200k US dollars of prize money.

Today Hackaday has written a post promoting their project and explaining what it is all about. Check out their post here http://hackaday.com/2015/02/19/ground-stations-are-just-the-beginning-the-satnogs-story and go and support this project by checking out the SatNOGS community.

The internal of the current SatNOGS ground station.

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