April 20, 2013

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.

DRM REE Noblejas Radio with RTL SDR (RTL2832), Nooelec Ham It Up Upconverter, SDR Sharp and DREAM

Watch this video on YouTube

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April 18, 2013

ADSB# Plugin for SDRSharp

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Update and Note: This plugin appears to be now dead. If you are simply looking for the ADSB# standalone program (not the plugin), it is located in the SDR# install folder from sdrsharp.com.
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A user by the name of darkscout.rm on the SDRSharp Yahoo group has posted version 3 of his ADSB# plugin for SDRSharp. The main purpose of this plugin is that it allows the waterfall to viewed at the same time as decoding, which may help with visually tuning the gain settings, or experimenting with ways to block out out of band interference. He has also added in a 1-bit error recovery by brute force option, which is used in dump1090 and may improve decode performance.

ADSB# is a standalone program to receive ADS-B signals and my ADS-B plugin does the same but from within SDR#. Continue reading →

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April 17, 2013

Homemade ADS-B Filter

Reddit user BigReid has posted on the Reddit rtl-sdr forums his homemade bandpass filter with a pass range of 1-1.2GHz for improving adsb reception. A bandpass filter blocks any interference from signal frequencies outside of the pass range. This might be useful for adsb if you experience a lot of interference from out of band signals at 1090MHz.

His filter is a hairpin filter, which can easily be etched onto a PCB board. You can find the PCB schematic files linked on the post.

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April 16, 2013

2-in-1 RTL-SDR and HF Upconverter on a Single PCB

A Hungarian hardware developer has been working on what appears to be a 2-in-1 software defined radio, combining the rtl2832u and E4000 tuner chips together with a HF upconverter all on the same PCB. The device is able to tune from 1MHz to 1.7GHz, and has two antenna connectors, one for the HF antenna, and another for the VHF/UHF antenna. Using the Google translation is difficult, but it seems the board has a protection diode, 100MHz oscillator, low noise amplifier (LNA), isolation between the two antennas, and also retains the ability to receive DVB-T and DAB broadcasts.

The developers article in Hungarian on this combined tuner can be found here, and a Google English translation here. Another version of the page which looks to be a product ordering page can be found here, and Google English translation here. We aren’t sure if the developer is still shipping these devices as the eBay listings have all gone down, but it seems you can order one by contacting the developer from the website.

Update 27 May 2013: Version 3 of this combined rtl-sdr can be now found for sale at this link. http://janielectronics.com/index.php?route=product/product&product_id=94.

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April 15, 2013

Using Unitrunker with SDRSharp

Trunking radio is a radio system where a finite number of frequency channels are shared between multiple radio users. This allows support of a much larger number of radio users. A special control frequency is used to determine which frequency a radio should be tuned to.

This all means that following a radio conversation with a software defined radio such as the rtl-sdr can be difficult, as the conversation can hop around multiple frequencies. Fortunately there is software called unitrunker which can listen to the control channel, and determine what voice frequencies need to be tuned to. More information about unitrunker and the signals it can decode is shown on this RadioReference wiki page.

A tutorial on how to set up unitrunker with SDRSharp has been posted here. Essentially, to follow trunked radio conversations you will need two rtl-sdr dongles (or any two software radios), unitrunker and virtual audio cable. One radio will be used for the control channel and unitrunker, and the other will be used for the listening to the voice channel. This can also be done with one software radio, and one hardware radio with discriminator tap if one have one of those. If you are trying to track digital voice communications, it can be done with one dongle and this is discussed in the tutorial too.

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April 14, 2013

RTL-SDR Used in a University Course

The University of California Berkeley has started using RTL-SDR in the course EE123: Digital Signal Processing. Every student in the class gets a DVB-T dongle and given the task of designing a SSTV transceiver system.

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April 14, 2013

RTL-SDR Running ADS-B on a Quadrocopter

Blogger John Wiseman has managed to get ADS-B decoding using an rtl-sdr stick working on his AR.Drone quadrocopter. The AR.Drones run on the Linux operating system, so he was able to compile and install the Linux ADS-B decoder dump1090 on his drone.

Although the reception was hampered by RF interference from the drones electric motors, it was still able to pick up a number of ADS-B signals.

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April 14, 2013

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.

However, the difficulty with direct sampling is that a hardware modification to the dongle is required. Also, the performance can not be expected to be as good as an upconverter without the addition of extra filtering circuits. RTL-SDR Blog V3 Note: Note that our RTL-SDR Blog V3 already has the direct samping mod done and built in, so no hardware modifications are required for those units! Just see the V3 users guide for information on activating direct sampling mode.

The direct sampling mode was originally discovered and discussed in this Google groups thread.