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More reception modes for the SiDRADIO & SDRs By JIM ROWE Wondering if there’s anything else you can do with your software defined radio (SDR) set-up using a DVB-T dongle – besides receiving AM, NFM, WFM, CW, SSB and DRM? Other applications are becoming available all the time. Already there’s one that lets you receive DAB+ digital radio and another to receive some of the many different types of narrowband digital mobile radio (DMR). M OST DVB-T dongles come with bundled software that allows them to be used for receiving SDTV and HDTV signals, as well as DAB+ digital radio and conventional FM signals. But if you’re using a dongle as part of an SDR set-up, it’s a bit messy to also use it for DTV/DAB+ reception on the same PC. That’s because you have to disconnect it and plug it into a different USB port from the one you are using for the SDR. This is necessary because the USB driver for DTV/DAB+/FM reception using the bundled software is quite different from the one that Zadig installs for use with SDR software. Fortunately, there is a way baround this problem. What we are going to do here is show you how to get DAB+ reception while leaving the dongle as part of an SDR configuration (or even as part of the SiDRADIO described in the October and November 2013 issues). In other words, you will no longer have to unplug the dongle and plug it into a different USB port. All you have to do is install and run some additional software. Now it’s true that most of the DVBT dongles use the Realtek RTL2832U COFDM demodulator chip, which already has internal ‘hardware’ to decode DAB+ digital radio signals. In fact, this function is used by the bundled software that comes with the dongles. However, as yet, the programmers 64  Silicon Chip working on SDR apps (applications) haven’t discovered how to make use of this internal hardware of the RTL­ 2832U chip. Instead, they use the RTL-SDR driver (installed by Zadig) to switch the chip into its ‘radio’ mode. In this mode, it simply passes on the quadrature (I and Q) samples coming from the dongle’s tuner chip and sends them to the PC via a USB cable. It’s here that the SDR application software (SDR#, ADSB#, Dream or whatever) does the decoding/demodulation. Eventually, someone is bound to work out how to make use of the RTL2832U chip’s ‘internal decoding hardware’ for DAB+ reception and more. But until then, you’re going to have to use the ‘software decoding’ TABLE 1: CURRENT VHF BAND III CHANNELS USED FOR DAB+ DRMTs IN AUSTRALIA METRO AREA CHANNELS USED ADELAIDE 9B, 9C BRISBANE 9A, 9B, 9C MELBOURNE 9A, 9B, 9C PERTH 9B, 9C SYDNEY 9A, 9B, 9C CHANNEL CENTRE FREQUENCY BANDWIDTH 9A 202.928MHz 1.536MHz 9B 204.640MHz 1.536MHz 9C 206.352MHz 1.536MHz NOTE: ALL OF THESE TRANSMISSIONS ARE VERTICALLY POLARISED DRMT = DIGITAL RADIO MULTIPLEX TRANSMITTER approach, if we want to receive DAB+ transmissions with dongle-based SDRs such as the SILICON CHIP SiDRADIO. Receiving DAB+ As luck would have it, a public domain software package which allows DAB+ signals to be received using a DVB-T dongle-based SDR has been made available in the last few months. Called “SDR-J” and released by Dutch programmer Jan van Katwijk, the latest version (V0.96 at the time of writing) is available as a free download from his website at www.sdr-j.tk Two versions of SDR-J are available: (1) a Linux version (as a suite of source code files) and (2) a Windows version which consists of a zip file containing the executables. Note, however, that the heavy processing requirements of DAB+ software decoding mean that you need a relatively modern computer to run it. Also, the Windows version is currently only suitable for 64-bit versions of Windows 7 or Windows 8. If you’re running a 32-bit version of Windows, you’ll still have to use your dongle’s bundled software for DAB+ reception – at least for the time being. Assuming you’re running a 64-bit version of Windows, you might want to try downloading and installing SDR-J V0.96 to see how it performs. While you’re downloading the software, you should also download Jan van Katwijk’s user manual from www. sdr-j.tk/dab-manual.pdf As mentioned, the software comes siliconchip.com.au as a zip file. To extract the files, you have to run dabreceiver.exe. This should install everything ‘ready to go’ and you’ll find a shortcut icon on your desktop labelled “DAB RADIO”. When you double click this icon, you’ll first see a command line dialog box open up – just like the one shown at the top of Fig.1. This box will display the actions of SDR-J’s software ‘engine’ as it proceeds. After a short time, it will be joined by a second window similar to the lower one in Fig.1. This is the control panel for SDRJ, although both it and the command line dialog box are displayed all the time that SDR-J is running. To begin using SDR-J, check the four rectangular buttons at lower left in the control panel window, just below the black ‘constellation’ display window at upper left. Look first at the button at far left and if it is not displaying “dabstick” as shown in Fig.1, click on the associated down arrow and select “dabstick” from the drop-down menu. Next, move along to the third button and confirm that SDR-J is currently set to look for DAB+ signals in BAND III (again, as shown in Fig.1). If not, click on its down-arrow and select BAND III from the drop-down menu. Before going further, check that Band III channel(s) are being used for DAB+ broadcasts in your area. At present, DAB+ signals are broadcast only in Adelaide, Brisbane, Melbourne, Perth and Sydney. Table 1 shows the channels used by the digital radio multiplex transmitters (or DRMTs) for DAB+ broadcasting in these metropolitan areas. Only channels 9A, 9B and 9C are currently being used, with only two of them in use in some of the smaller capitals. If you find this a bit puzzling, bear in mind that up to 18 different DAB+ signals can be multiplexed onto a single DRMT ‘channel’ and each channel is 1.536MHz wide. Just how many DAB+ signals are packaged into each DRMT channel block depends on the data bit rate used by each one. Once you know which DRMT channels are present in your area, you can continue setting up SDR-J. First, click the down-arrow associated with the fourth button at lower left and select the channel you want from the dropdown menu. Fig.1 shows that channel 9C has been selected in our case. This channel carries the ABC and SBS DAB+ broadcasts in Sydney. siliconchip.com.au Fig.1: SDR-J first opens up a command line dialog box, followed by a second control panel window. Both are displayed while ever SDR-J is running. Then click the large START button at centre right of the control panel and SDR-J will start searching for DAB+ signals in the selected channel and you should see each of the signals it finds in the ‘list box’ just to the left of the START and QUIT buttons. Fig.1 shows some of the signals found within channel 9C in Sydney in the list box. It also shows the spectrum display that SDR-J has produced for Sydney channel 9C DAB+ multiplex, ie, in the spectrum box at upper right of the control panel window. Next, look at the long rectangular button at bottom right on the control panel, which initially will probably be labelled “select output”. Click on its down arrow and select one of the options from the drop-down menu. In most cases, this will be an audio output device like “Microsoft Sound Mapper – Output” or “Speakers (Realtek High Definition)”. Then click on one of the entries shown in the list box, to select it. You should then see some activity in SDRJ’s upper command-line dialog, while it achieves synchronisation with that signal. Finally, after a few seconds, you should hear that signal’s audio from your PC’s speakers. And that’s all there is to it! If you want to change to another station in the same multiplex, all you need do is click on it in the list box. After a few seconds delay, you’ll then start to hear the audio from that station. Other DRMT multiplexes What if you want to search for signals in one of the other DRMT multiplexes in your area? That’s also quite easy. All you need do is select the channel ID for the multiplex you want (eg, say 9A or 9B) by clicking on the down-arrow at the end of the fourth button at lower left. SDR-J will then generate a new list of DAB+ stations (ie, the stations associated with that multiplex) in the list box and show a new spectrum display at upper right. Then all you need to do to receive a station is click on its name in the list box, as before Other controls What about all of those other controls and displays scattered around SDR-J’s control panel? Jan van KatwiDecember 2013  65 VHF/UHF ANTENNA HF ANTENNA RF PREAMP AND PRESELECTOR HF UPCONVERTER DVB-T DONGLE Fig.2: the hardware/software configuration for a DMR (Digital Mobile Radio) receiving set-up using SDR#, Virtual Audio Cable (VAC) & DSD. The DVB-T dongle can be in the SiDRADIO or free-standing. USB CABLE ORIGINAL SDR SOFTWARE SDR APPLICATION (I.E., SDR#) RTL-SDR DRIVER ADDED SOFTWARE FOR DMR VIRTUAL AUDIO CABLE DMR DECODING APP (I.E., DSD) (INSTALLED BY ZADIG) SiDRADIO ‘FRONT END’ PC SOUND CARD OR ONBOARD DACS INTERNAL OR EXTERNAL AMPLIFIERS SPEAKERS EXTENDED SDR CONFIGURATION FOR DMR RECEPTION USING DSD jk’s user manual isn’t all that helpful when it comes to many of these, so you will have to work them out for yourself. But some are fairly self-evident if you look at them closely – or at their label, where they have one. For example, in the lower centre of the control panel shown in Fig.1, you’ll see SDR-J’s title: “sdr-j DAB(+) 0.96”. And below this you can see the name of the station I had tuned to: “ABC Classic FM DAB+”, with its programming language and summary shown to the left. Just above the SDR-J title, you can see two numbers, displayed in 7-segment format: 196617 and 2048000. The first of these apparently indicates the length of the data frames detected in the multiplex signal (it should normally read about 196617, as shown), while the second shows the total bit rate used in that multiplex. The latter always seems to read 2048000, suggesting a total bit rate of 2.048Mbps. Just above the list box, you can also see the label “SY ABC&sbs RADIO”, which is presumably the name of the DRMT multiplex signal itself. At lower right, just to the left of SDR-J’s “Output Select” button, there’s a small box displaying a single digit (“8” in Fig.1). Just to its left, there’s a label reading “dabstick gain” and if you click on one or other of the small direction arrows on its right, you’ll find that the spectrum display moves up or down as the displayed gain digit increases or decreases. This seems to be the way SDR-J allows you to adjust the RF gain of your DVB-T dongle, for optimum DAB+ reception (presumably “dabstick” is what DVB-T dongles are called in many parts of Europe). One last suggestion: the row of display boxes at bottom left has fairly 66  Silicon Chip cryptic labels, making it difficult to work out their significance unless you’re an expert on DAB+. However the “bit rate” label just below the fifth one from the left suggests that it shows the bit rate of the particular signal in the multiplex currently being decoded. In this case, it’s showing “80”, while the third last line in the command line box above also shows 80 as the bit rate of the ABC Classic FM signal being received at the time. This means that the ABC uses a bit rate of 80kbps for this signal, which is encoded using the HE-AAC compression codec. Receiving DMR OK, so much for using SDR-J to receive DAB+ broadcasts. Now let’s take a brief look at yet another application for SDRs based on a DVB-T dongle. As Kevin Poulter explained in his article on “Narrow Band Digital TwoWay Radio” in the October 2013 issue of SILICON CHIP, professional 2-way radio communications is rapidly making the transition from analog to digital technology. This is because digital encoding offers more efficient use of the spectrum, allowing more users to be crammed into limited spectrum space. So narrowband 2-way radio is fast becoming “DMR” or digital mobile radio. That may sound simple but the catch is that there are many different digital encoding formats and modulation modes. These can make it quite difficult to receive and decode DMR signals – especially as many of the formats allow for the signals to be encrypted or scrambled for high security communications like those of the military, intelligence services and police. For example, there’s NXDN or Next Generation Digital Narrowband tech- nology, developed jointly by Icom and JVC Kenwood. This allows two 6.25kHz wide narrowband digital channels to be fitted into a single 12.5kHz wide VHF communications channel. Then there’s Project 25 (P25/APCO25), a suite of digital radio communications formats which were developed in the USA to allow reliable and secure 2-way radio communications within specific federal and state government agencies and between these agencies. Another variant is the set of protocols developed by the European Telecommunications Standards Institute (ETSI) for professional DMR, or ‘PMR’. There’s also Motorola’s DMR/MOTOTRBO, ProVoice EDACS, and so on. Fortunately, an open source software package recently became available to allow a DVB-T based SDR setup to receive and decode at least some of this plethora of DMR formats and modulation systems. Called Digital Speech Decoder or “DSD” for short, it can decode the following DMR formats and modulation types (providing they’re not encrypted): • P25 Phase 1 • ProVoice EDACS digital voice • NXDN – 9600-baud/12.5kHz NEXEDGE and 4800-baud/6.25kHz NEXEDGE/IDAS • X2-TDMA – Motorola public safety TDMA • DMR/MOTOTRBO • C4FM modulation, GFSK modulation and QPSK/LSM modulation The DSD package can be downloaded from: http://wiki.radioreference.com/index.php/Digital_Speech_ Decoder_(software_package) The version you’ll need in order to run DSD on Windows PCs is currently called “Windows Port With P25/DMR Filter 1.6.0 Beta”. When you download this file, you’ll siliconchip.com.au Software For SDR Applications Using DVB-T Dongles & Where To Find It A. For basic SDR (AM, WFM, NFM, CW-L, CW-U, USB, LSB, DSB reception) you’ll need: (1) The RTL-SDR driver, which is installed using the installer program Zadig. A compressed file containing Zadig can be downloaded from sourceforge.net/projects/libwdi/files/Zadig but note that (a) there are two versions of Zadig, one for Windows XP and the other for Windows 7; and (b) both versions can only be downloaded as compressed files in ‘.7z’ format, so they must be extracted using 7-Zip rather than Winzip. 7-Zip can be downloaded from either sourceforge.net or from www.7-zip.org but note that it too comes in two versions – one for Windows XP and the other for Windows 7. (2) An SDR decoding and display application, such as SDR#. This is open source and comes in three separate files – two of which can be downloaded from http://sdrsharp.com/downloads, while the third (rtlsdr.dll) must be downloaded from the Osmocom website at http://sdr.osmocom.org/trac/wiki/rtl-sdr/ For more information on downloading, installing and using these basic SDR software components, refer to our article in the May 2013 issue of SILICON CHIP. B. For receiving, decoding and displaying the ADS-B broadcasts from aircraft flying overhead, you’ll need: (1) the RTL-SDR driver which is installed using the installer program Zadig (see item A.1 above). (2) An ADS-B decoding application like ADSB# or RTL1090. These are both open source and ADSB# can be downloaded from http://sdrsharp.com/downloads/adsbsharp.zip There’s also a quickstart guide for ADSB# written by Henry Forte and available as a pdf file from http://www.atouk.com/ wordpress/?p=247 The RTL1090 application can be downloaded from http://rtl1090.web99.de/ (3) An ADS-B processing and display application like ADSBScope, Virtual Radar Server or PlaneSpotter. ADSBScope can be downloaded from http://www.sprut.de/electronic/pic/projekte/adsb_en.html#downloads; Virtual Radar Server from http://www.virtualradarserver.co.uk; and PlaneSpotter from http://www.coaa.co.uk/planespotter.htm For more information on downloading, installing and using these ADS-B software components, refer to our article in the August 2013 issue of SILICON CHIP. C. For receiving and listening to DRM (Digital Radio Mondiale) signals, and decoding them via RTL-SDR, you’ll need: (1) The RTL-SDR driver which is installed using the installer program Zadig (see item A.1 above). (2) An SDR decoding and display application such as SDR# (see item A.2 above). (3) A ‘virtual audio cable’ program like Virtual Audio Cable (VAC), to direct the digital audio output from SDR# to the input of the DRM decoding application. Virtual Audio Cable can be downloaded from either software.muzychenko.net/vac.htm or download.cnet.com/Virtual_Audio_Cable (4) A DRM decoding/receiver application, like DREAM. This open source application can be downloaded from sourceforge. net/projects/drm/files/dream/ You will also need the precompiled faad2_drm.dll, which is used for DRM decoding using the AAC codec. This must be downloaded from: https://mega.co.nz/#!m5RUHIDQ!SqcGUBSGMFSTAm09XX78RDYR oIJW0T545QQRJ_dFuE For more information on downloading, installing and using these software components, see the article in the November 2013 issue of SILICON CHIP. D. For receiving and listening to DAB+ digital radio broadcasts as described in this article, you’ll need: (1) A PC running a 64-bit version of Windows 7 or Windows 8. (2) The Windows version of the DAB+ receiving application SDR-J V0.96, developed by Dutch programmer Jan van Katwijk and available free from his website at www.sdr-j.tk There’s also a user manual for it at www.sdr-j.tk/dab-manual.pdf E. For receiving and listening to digital mobile radio (DMR) transmissions, as described in this article, you’ll need: (1) The RTL-SDR driver which is installed using the installer program Zadig (see item A.1 above). (2) An SDR decoding and display application such as SDR# (see item A.2 above). (3) A ‘virtual audio cable’ program like Virtual Audio Cable, to direct the digital audio output from SDR# to the input of the DMR decoding application (see item C.3 above). (4) A digital speech decoder application like Digital Speech Decoder (DSD). This is an open source program and can be downloaded from http://wiki.radioreference.com/index.php/Digital_Speech_Decoder_(software package)#Downloads The version to download for PC’s running Windows is currently “Windows Port with P25/DMS Filter 1.6.0 Beta”. (5) The Linux emulation layer cygwin1.dll, which is needed by Digital Speech Decoder (DSD) to run on Windows systems. This can be downloaded from http://cygwin.com/install.html by clicking on the link “setup-x86.exe”. siliconchip.com.au December 2013  67 Fig.3: a typical DMR signal as shown in the spectrum and waterfall displays of SDR#. Note that you have to select Virtual Audio Cable (VAC) as the output option (see text) to send the signal to the PC for software decoding. find it’s an executable called DSD160. exe, which you can install simply by creating a folder called (say) C:\Program Files\DSD\ and then copying DSD160.exe over into it. Don’t try to run it as yet though, because DSD was originally written to run under Linux. As a result this Windows ‘port’ needs a special Linux emulation program in order to actually run on Windows. This emulation program is an application extension called cygwin1.dll, which is part of a suite of programs you need to download and install separately from: http://cygwin. com/install.html All you need to do is go to this page and click on the link setup-x86.exe (note: there’s another link called setupx86_64.exe but this is not needed for running DSD because the latter is a 32-bit package). When the Cygwin package has been downloaded and installed (it automatically installs itself in the root directory, usually C:\cygwin\), you’ll find the all-important cygwin1.dll file in the \bin subdirectory. The next step is to copy this file and paste it into the same folder as DSD itself (ie, C:\ Program Files\DSD\). Note that this program doesn’t communicate directly with your DVB-T dongle via the RTL-SDR driver. In68  Silicon Chip stead, like Dream (the DRM30 decoding application that we looked at in the November 2013 issue of SILICON CHIP), it ‘listens’ to the digital audio output from your SDR application (eg, SDR#). In order to do this it needs Virtual Audio Cable (VAC), the same miniport digital audio driver used by Dream. So before you can run DSD, you’ll need to download and install both SDR# and VAC – and perhaps even the RTL-SDR driver, if you haven’t already done so. Fig.2 shows the overall hardware/ software configuration for a DMR (Digital Mobile Radio) receiving setup using SDR# plus VAC plus DSD. Note that although this diagram shows the DVB-T dongle fitted inside our SiDRADIO project, the dongle can be free-standing for DMR reception if you wish. That’s because you’ll only find DMR signals on the VHF and UHF bands at the moment. Receiving DMR – or trying The procedure for using your SDR set-up to receive DMR is to first start up SDR# with its digital audio going to your PC’s speakers in the usual way. This allows you to search around on the VHF and UHF bands for any likelylooking signals. The best places to start in Australian metropolitan areas are in the 162-174MHz, 470-520MHz and 860-890MHz regions. By the way, it’s a good idea to set SDR# for NFM reception, with a filter bandwidth of either 12.5kHz or 25kHz. Some of the reference information on DMR reception also suggests that the Filter Order should be set to a low figure, such as 10, instead of the default 300 or 400. Search around on one of these bands using SDR# until you find a signal that looks a bit like that in the centre of the display in Fig.3. If it’s a DMR signal, you won’t hear any audio at this stage apart from digital noise. Next click the Stop button at top left in the SDR# dialog and then move down to the Output label in the Audio section below. If you now click on the down-arrow in the text box to its right, you will be presented with a drop-down list showing “Virtual Audio Cable” (VAC) as one of the output options. If you click this option, SDR# will now send its digital audio output to VAC instead of the speakers. Before you set SDR# running again, fire up DSD by clicking on its icon on your desktop. You’ll then see its command-line interface, with the heading “dsd160” – see Fig.3. Now when you click the “Play” button at top left in the SDR# dialog, you’ll probably see some activity in the DSD dialog box as well. Just what you’ll see in the DSD dialog depends on what type of signal you’ve tuned to, its signal strength, the DMR encoding system being used, the modulation mode and whether or not the signals are encrypted/scrambled. The same qualifications apply as to whether or not you’ll hear any audio. In my case, I spent quite a few hours trying to find a DMR signal that I could decode with very little success. I did receive a few seconds of audio on one occasion but that was it. In fact, my impression is that a lot of the DMR signals nominally available in my area are either encrypted or ‘locked up’ in trunking systems. There is an open-source program called “UniTrunker”, which is supposed to allow you to decode some kinds of trunked DMR. You can download it from http://wiki.radioreference.com/index.php/UniTrunker but I can’t say whether or not it’s worth the effort. In my opinion, it’s for the real enthusiast only and you’d better SC have a lot of patience! siliconchip.com.au