Category: RTL-SDR

Watching DVB-T TV and Using SDR Mode at the same time with two RTL-SDRs

Normally if you want to use the RTL-SDR as an SDR on Linux you install the SDR drivers, and blacklist the Kernel's built in DVB-T drivers to prevent them from taking over the RTL-SDR. Once blacklisted, no RTL-SDR plugged into that system can be used for DVB-T watching unless the blacklist is removed. But if the blacklist is removed, SDR mode cannot be used. So it's impossible to use one RTL-SDR as an SDR, and one for DVB-T TV at the same time.

However now, Hayati A. has submitted news about his RTL-SDR driver patch which allows you to run SDR mode and DVB-T TV mode at the same time with two RTL-SDR dongles.

The idea behind allowing two dongles to operate in separate modes is that one dongle needs to have the PID code stored in its EEPROM changed to a code which was recently registered by Hayati. The dongle with this PID code won't be recognized as a DVB-T device by Linux, and so can only be used for SDR. An dongle with the stock EEPROM can then be plugged in and used for DVB-T.

The patch has been accepted into the development branch of the librtlsdr drivers and the Readme notes read:

  • A special USB vendor/product id got reserved at http://pid.codes/ : 0x1209/0x2832 
  • for such devices the linux kernel's DVB modules are not loaded automatically, thus can be used without blacklisting dvb_usb_rtl28xxu below /etc/modprobe.d/
  • this allows to use a second RTL dongle for use with DVB in parallel 
  • the IDs can be programmed with 'rtl_eeprom -n' or 'rtl_eeprom -g realtek_sdr'

Note that the DVB-T drivers in Linux should not be blacklisted if you are doing this. Also some cheaper RTL-SDR models don't come an EEPROM, and those models can not do this.

YouTube Tutorial: Using RTL-SDR on an Android Smartphone

Over on YouTube, channel Null Byte has uploaded a video showing us how to use an RTL-SDR V3 on an Android smartphone. In the video he discusses the hardware and software required to get started on Android and demonstrates the free SDRoid Android app (based on RFAnalyzer) by tuning to several signals including a voice signal. Later in the video he also shows an ADS-B app for receiving aircraft positions. The video is intended for people new to RTL-SDR so it is a little basic, but it's a great introduction.

He notes that the next video (which will probably be released in a week) will show RPiTX being used with the RTL-SDR.

Use an RTL-SDR Software-Defined Radio Receiver with an Android Smartphone [Tutorial]

An Overview on RF Direction Finding with RTL-SDRs

Thanks to K2GOG of the Hudson Valley Digital Network for writing in a sharing with us his latest blog post which is a useful overview of some direction finding techniques that can be used with RTL-SDR dongles. RF direction finding is the act of using a radio to determine the physical location of a signal.

In his post K2GOG mentions our successfully crowd funded KerberosSDR which will be shipping in January next year. KerberosSDR is our 4x coherent RTL-SDR, and one possible application is to use it as a four antenna phase coherent direction finder. K2GOG explains the phase coherent concept in his post quite elegantly.

While looking over KerberosSDR, K2GOG was also reminded of another direction finding technique called heat mapping which can be performed with a single RTL-SDR. This process involves driving around with an RTL-SDR and GPS logger, measuring the signal power as you drive and combining it the current GPS coordinates. From that data a heat map can be generated, which shows where the signal is the strongest, and therefore where the likely source is. The RTLSDR Scanner application by eartoearoak makes doing this easy, and in his post K2GOG provide a short tutorial on setting it up.

A heatmap generated by K2GOG with an RTL-SDR, GPS and RTLSDR Scanner.
A heatmap generated by K2GOG with an RTL-SDR, GPS and RTLSDR Scanner.

An Open Source VOR Receiver for Airspy and RTL-SDR

Thank you to Thierry Leconte (TLeconte) for writing in and submitting his new command line based open source software called vortrack. Vortrack is a simple VOR decoder which calculates the angle towards the VOR. It is compatible with both RTL-SDR and Airspy radios, and runs on Linux.

In the past we've seen several other posts about RTL-SDRs being used to decode VOR signals, but Thierry's implementation appears to be the easiest way to get a bearing straight away. You'll get the most use out of the software if you install it on a portable device like a Raspberry Pi and take it out for a drive as you'll be able to see the VOR angle changing then.

VOR stands for VHF Omnidirectional Range and is a way to help aircraft navigate by using fixed ground based beacons. The beacons are specially designed in such a way that the aircraft can use the beacon to determine a bearing towards the VOR transmitter. VOR beacons are found between 108 MHz and 117.95 MHz, and it's possible to view the raw signal in SDR#.

A DVOR Ground Station at an Airport. Source Wikipedia.
A DVOR Ground Station at an Airport. Source Wikipedia.

Motherboard Article: Creating an IMSI Catcher with an RTL-SDR

Motherboard, an online technology magazine has recently run an article titled "With $20 of Gear from Amazon, Nearly Anyone Can Make This IMSI-Catcher in 30 Minutes". The article describes how an RTL-SDR together with the IMSI-Catcher Linux software can be used to collect IMSI numbers from cellphones connected to a nearby cell tower. The IMSI is a unique number assigned to each SIM card and collecting this data could be used to identify if someone is in the area covered by the cell tower.

The IMSI-Catcher software only works with the older 2G GSM signals which are now being phased out in some countries and are relatively unused in others. Also unlike more advanced IMSI-Catchers which create a fake cell tower signal, the RTL-SDR based IMSI-Catcher can only collect IMSI numbers when the cellphone first connects to the cell tower.

One of our older posts with a YouTube tutorial video explains the RTL-SDR IMSI Catcher in more detail. 

IMSI-Catcher Python Script
IMSI-Catcher Python Script

Measuring Broadcast FM Multipath Distortion with an RTL-SDR

Over on GitHub user jj1bdx has just released a new tool called rtl_power-fm-multipath which can be used for estimating broadcast FM multipath distortion with an RTL-SDR. Broadcast FM multipath is caused when a signal is received from multiple directions due to it reflecting off and refracting through physical objects like buildings and terrain. As the reflected/refracted signals will be delayed it can cause echo like distortions in the RF signal which can cause issues like poor digital decoding, poor FM audio reception and ghosting in analogue video.

The multipath distortion estimation method works by measuring the ratio of the strength of direct/reflected radio waves which results in the desired/undesired (D/U) ratio. This measurement method was proposed by Komiya87 and JushinFM who both wrote papers in Japanese describing the method. In summary the methodology is:

  • Measure the maximum peak strength for +-50kHz spectrum of the target FM station
  • Obtain the maximum value (Lmax) and minimum value (Lmin) within the spectrum
  • Obtain the ratio of the maximum and minimum values L = Lmax / Lmin (note: Lmax and Lmin are real values (not in dB), and L must be > 1)
  • The estimated D/U ratio R = (L+1) / (L-1) (in the real value, not in dB)

The rtl_power-fm-multipath program is based on rtl_power and works by using rtl_power to record power measurements for 5 minutes, then sending the data to a peakhold function which computes the maximum power value for each frequency, and then calculations the distortion ratio.

An example of Multipath Distortion on a DAB+ Signal. From Gough Lui's post https://goughlui.com/2015/03/28/trip-to-hk-cn-2014-part-5-rtl-sdr-more-radio-ais-night-photos/
An example of Multipath Distortion on a DAB+ Signal. From Gough Lui's post at https://goughlui.com/2015/03/28/trip-to-hk-cn-2014-part-5-rtl-sdr-more-radio-ais-night-photos

Es’hail-2: First Geostationary Satellite with Amateur Radio Transponders Successfully Deployed

Today SpaceX have successfully launched and deployed the Es'hail-2 satellite which is now in geostationary orbit. This launch is special for amateur radio enthusiasts because it is the first geostationary satellite that contains an amateur radio transponder on it. The satellite is positioned at 25.5°E which is over Africa. It will cover Africa, Europe, the Middle East, India, eastern Brazil and the west half of Russia/Asia. Unfortunately, North America, Japan, most of South America, Australia and NZ miss out.

Coverage of Es'hail 2
Coverage of Es'hail 2

The satellite has a two bandwidth segments, a 250 kHz narrow band for modes like SSB, FreeDV, CW, RTTY etc, and a 8 MHz wide band for digital amateur TV (DATV) modes like DVB-S and DVB-T.

The downlink frequencies are at 10 GHz so a low cost TV LNB could be used as the antenna. For receiving the narrowband modes, an RTL-SDR or similar SDR could be used, and for the 8 MHz DATV modes a standard DVB-S2 set top box can be used to receive and decode the video. For uplink, the transmission frequency is at 2.4 GHz.

According to the commissioning order of the satellite, it is expected that the AMSAT transponders will be activated only after all tests have been passed, and after other higher priority commercial telecommunications systems have been activated. This is expected to take about 1-2 months.

2018: Es'hail-2 and its amateur radio payload - Graham Shirville (G3VZV) & Dave Crump (G8GKQ)

An Overview of Aircraft Communication Modes from HF to UHF

Over on YouTube icholakov has uploaded an informative video that gives an overview of the main communication modes that aircraft use from HF to UHF. In the video he also gives examples of those modes being received and decoded with an SDR.

The modes that he explains and demonstrates are VHF voice, VHF ATIS automated weather, ACARS short data messages, HF voice, HF automatic weather, HF data selective calling (SELCAL), HF data link (HFDL) and UHF ADS-B aircraft positioning.

Monitoring airplane communications