Tutorial: How to Use a DTT Key to Turn it into an SDR Receiver

Introduction

A Software Defined Radio (SDR) is a radio receiver and potentially transmitter primarily realized through software and to a lesser extent by hardware. This tutorial focuses on using the RTL2832U chipset from Realtek. Antii Palosaari discovered that this chip transmits raw frames for DAB, DAB+, and FM demodulation. The output is sampled at 8 bits, allowing a theoretical throughput of 3.2 MS/s, with a practical maximum of 2.8 MS/s.

While a DTT key only allows reception, it is forbidden to transmit on certain frequencies with specific power levels. Reception is not restricted. Sensitive communications (military, police, etc.) are encrypted.

This tutorial is compiled from various sources and personal experience. Limited documentation is available in French, so an effort has been made to create a comprehensive guide. Reference tutorial: http://rtlsdr.org/softwarewindows

Prerequisites

It is essential to choose the correct DTT (DVB-T) keys. An evolving list of compatible and incompatible keys is available at: http://www.reddit.com/r/RTLSDR/comments/s6ddo/rtlsdr_compatibility_list_v2_work_in_progress/

Some models offer an ideal configuration: the combination of RTL2832U and E4000 chipsets. However, the E4000 manufacturer's bankruptcy has made models with this chip rare. The E4000 chip's advantage is its high sensitivity and wide frequency band from 50 to 1700 MHz. These keys are hard to find in stores; online purchase is usually easier.

A Conceptronic USB 2.0 Digital HDTV Receiver CTVDIGUSB2, costing less than €25, was found with the indispensable RTL2832U chip but without the E4000, instead featuring an FC0013 chip. This works for the tutorial.

You will need a computer (minimum Pentium 4 at 1 GHz, or a sufficiently fast Atom processor). All Windows versions from XP to Seven are compatible. You will also need the .Net 3.5 library, which is likely already installed on your PC. If not, a Google search will help you find it.

Initially, this modification was only possible on Linux, but libraries have been developed for Windows. The software used is SDR# (pronounced SDR sharp). It is recommended to use the development version of SDR#, not the official stable version. Additional libraries will be required because some libraries used to run the RTL/SDR system are not open-source, and their inclusion would prevent SDR# from being classified as open-source.

The second essential software is Zadig. This program is used to replace the key's driver (automatically installed by Windows upon first insertion) with a generic USB driver. This allows bypassing the limitations imposed by the manufacturer's driver.

Installation

First, do not install the driver provided on the CD that comes with the DTT key, as it can cause problems.

If possible, open the plastic casing of the key and carefully examine the inscriptions on the visible chips on the printed circuit board. Ensure you do not damage anything. Look for the reference RTL2832U on one of the chips; this is crucial. If you see E4000 on another chip, you are fortunate. Otherwise, chips like FC0012 or FC0013 will also work. Without the Realtek RTL2832U chip, the key will only function for watching television.

If you are unsure, follow this tutorial. If it doesn't work, your key might be incompatible.

1. Insert the DTT key into a USB port on your computer. Allow Windows to install its default driver. Do not install the driver from the CD.
2. Download version 2.0.1.154 of Zadig from http://sourceforge.net/projects/libwdi/files/zadig/. Do not download the latest version, as it may not perform the required operation. Use 7-Zip (http://www.7zip.org/) to extract Zadig files.
3. Open the Zadig software.
4. Click on "Options" and select "List all devices".
5. Select "Bulk-In, Interface (Interface 0)". If this line does not appear, there might be an issue with the key. Try a different USB port or restart your PC. If problems persist, the key may be incompatible.
6. To the right of the green arrow, ensure "WinUSB" is selected. Do not choose libusb or libusbk. In the "USB ID" section, verify that the displayed VID/PID code matches your key model's code found at http://rtlsdr.org/hardware-usb. Click "Reinstall Driver". If prompted to trust the new driver, accept it.

Note: USB ports might be managed independently by Windows. If you performed the Zadig operation on a specific USB port, use that same port for future RTL/SDR activities. For classic TV viewing, use a different USB port, which will utilize the Windows Media Center driver.

Now, install SDR#. Some adjustments are necessary.

7. Download the development version of SDR# (SDR# Dev, not the latest stable version) from http://sdrsharp.com/index.php/downloads. Extract the downloaded folder to a directory of your choice (e.g., your Desktop, avoiding protected folders like C:/Program Files). There is no installer to run.
8. SDR# supports other hardware besides DTT keys. As mentioned, RTL/SDR libraries are not included with SDR# due to licensing issues. You need to install them manually. Download the first package: http://sdr.osmocom.org/trac/raw-attachment/wiki/rtl-sdr/RelWithDebInfo.zip
9. Open the downloaded zip file, navigate to the "rtl-sdr-release" folder, then the "x32" folder. Copy the files "rtlsdr.dll" and "libusb-1.0.dll". Paste them into the SDR# directory created in step 7.
10. Open the "SDRSharp.exe.config" file in a text editor. Locate the line: <!-- <add key="RTL-SDR / USB" value="SDRSharp.RTLSDR.RtISdrIO,SDRSharp.RTLSDR" /> -->. Remove the `` at the end. If the line is not found, add the following line among similar ones: <add key="RTL-SDR / USB" value="SDRSharp.RTLSDR.RtISdrIO,SDRSharp.RTLSDR" />. Save the file. It is advisable not to place the SDR directory within "C:\Program Files" to avoid potential bugs.
11. Almost done. Download the additional libraries from http://sdrsharp.com/downloads/sdr-nightly-rtlsdr.zip. Extract this downloaded folder into the SDR directory from step 7. Overwrite any existing files if prompted.
12. Installation is complete. Launch SDR# by opening "SDRSharp.exe" in the SDR directory.
13. Ensure your key is plugged into the same USB port used during the Zadig steps. To listen to FM radio, check "WFM" (Wide FM). Set the listening frequency to 88,000,000 Hz (88 MHz). In the dropdown list, replace "Other" with "RTL-SDR / USB". If everything is correct and your key is compatible, the "Front End" button will become clickable. Enable your computer's sound and click the "Play" button. Click on the red areas in the spectrum display to tune into signals.

Note: If the "RTL-SDR / USB" option is missing, there might be an error in the configuration file (step 10). If the option appears but an error message occurs, a library might be missing, the Zadig steps may have been performed incorrectly, or the key might be plugged into the wrong USB port.

Explore other listening modes, frequencies, and improve your antenna. You can discover the electromagnetic spectrum around you. Example usage video: http://youtu.be/tqUPj852FFY

Overheating: To prevent overheating, small aluminum pieces from cans can be cut and folded to act as heatsinks. Attach these heatsinks to the chips (avoiding electrical contacts) using super glue or strong adhesive. Transparent nail polish has also been used successfully.

For Macbook users with Windows installed via Bootcamp, these steps can be followed without issues.

In a future tutorial, the process of decoding digital transmissions like POCSAG using the PDW software will be covered.