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Using the SiDRADIO to receive DRM30 broadcasts By JIM ROWE Guess what! Here’s yet another use for DVB-T dongle-based SDRs like our SiDRADIO project: receiving DRM30 digital radio broad­ casts. All you need is the SiDRADIO with your PC running an application like SDR#, plus some additional decoding software which can be downloaded from the internet. E LSEWHERE IN this issue, we have an article on the technology of DRM digital radio. This second article shows how to use our SiDRADIO project (also in this issue) to receive and decode DRM broadcasts. It can also be used with the SDR (software defined radio) using a DVB-T dongle described in the May 2013 issue of SILICON CHIP along with the LF-HF Up-Converter described in the June 2013 issue. If you have already been using your SiDRADIO-based SDR to receive AM or SSB signals on the MF or HF bands, using an app like SDR#, you’ll be happy to hear that you can use exactly the same set-up for DRM30 reception – just by installing some more freelydownloadable software. That sounds pretty straightforward but it isn’t quite that easy, unfortunately. Although the additional software you’re going to need for DRM30 reception can be downloaded freely via the internet, installing it in your PC 64  Silicon Chip (and configuring it) can be a bit tricky. In fact, it’s at least as tricky as installing the original RTL-SDR driver and software components for SDR reception – if not more so. And some of the additional software is not well supported by clearly-written installation and/or operating information, either. Never fear though because this article shows how it can be done. I have spent a fair bit of time and effort (AKA trial and error) finding out how to install and use the DRM reception software successfully and now I have figured out the best way to do it . . . The basic idea To begin, take a look at the flow diagrams shown in Fig.1. The upper diagram (A) shows the flow of data in an SDR set-up using a DVB-T donglebased front end like our SiDRADIO, hooked up to a PC running the RTLSDR USB driver and an application like SDR#. This is exactly the same set-up we presented in the ‘Getting Into SDR’ article in the May 2013 issue, apart from the SiDRADIO box replacing the original daisy chain of an active HF antenna driving an upconverter driving the DVB-T dongle. In this basic configuration, the digital output stream from SDR# is passed directly to the PC’s sound card or onboard DACs, and then via internal or external amplifiers to the speakers. Now look at Fig.1(B), which shows the extended configuration needed for DRM30 reception. As you can see, it’s exactly the same as (A) right up to the output from SDR#. Instead of being passed straight to the sound card DACs as before, the digital output stream from SDR# is now fed to the input of the DRM decoding application DREAM, via another piece of software labelled ‘Virtual Audio Cable’. It’s the decoded output from the DREAM app which is then passed to the sound card DACs and used to drive siliconchip.com.au Fig.1: this diagram shows the basic SDR configuration at (A) and the revised configuration for DRM30 reception at (B). The hardware remains the same but you have to add Virtual Audio Cable & DREAM decoding software. the speakers. In fact, the only difference between the two configurations is that for DRM30 reception, we need to install those two further software components: Virtual Audio Cable and DREAM. Virtual Audio Cable is actually a Windows “miniport” driver written to conform to Microsoft’s Windows Driver Model (WDM). It performs the function of setting up one or more ‘virtual cable’ ports, which allow one Windows software application to send a digital audio stream to another application – rather than to a real port like the inputs of the sound card DACs or a USB port connected to the input of external ‘USB speakers’. So you can think of Virtual Audio Cable (or VAC) as simply a driver utility, which we use to pass the digital audio data stream from SDR# directly through to the input of the DREAM application, instead of to the sound card DACs as before. By the way, VAC was written by Russian programmer Eugene Muzychenko some years ago and has been updated and upgraded by him many times. His latest version is V4.13, which was released in July 2013. A trial version of VAC can be freely downloaded either from his website or from other download sites such as CNET – more siliconchip.com.au about installing this software shortly. Before we actually get going with the software downloading and installation, I want to warn you that because of space limitations, we won’t go through the steps involved in downloading and installing the basic SDR software shown in Fig.1(A). These software installation steps were all explained in considerable detail in the May 2013 issue of SILICON CHIP, so if you haven’t done this as yet you’ll need to refer to that earlier article. In the present article, we’re going to assume that you have already installed the basic software for SDR and just want to extend your SDR set-up for receiving DRM30 as well. The new software The first additional software component you’ll need is Virtual Audio Fig.2: once Virtual Audio Cable is installed, it should appear in the Audio section of SDR# (listed here as [MME] Virtual Cable 1). November 2013  65 Fig.3: you need to download faad2_drm.dll from www.mega.co.nz (see text). This dll file must then be copied to the folder where you installed DREAM. Cable. As mentioned above, a trial version of VAC can be downloaded at no cost from either Mr Muzychenko’s website or from the CNET website (see the Useful Links panel) but be warned that this version has the irritating property of injecting a female voice saying “trial version” into the digital audio stream from time to time. This can disrupt DRM decoding, so I suggest you purchase and download the fully-functional version online from his website. It costs between A$26.50 and A$52.70, depending on the level of online support you choose. For most people the Basic Support version is probably quite sufficient and this costs A$36.85. Fig.4: the waterfall display in SDR# when the software is set to tune a DRM30 signal from NZRI centred on 15.720MHz. SDR#’s displayed frequency is 15.715MHz (ie 5kHz below the centre frequency), as shown by the large digits just above the spectrum display window (see text for explanation). 66  Silicon Chip VAC4.13 downloads as a compressed zip file. To install it on the machine you’re using for SDR and DRM30 reception, unzip the download file into an empty folder on this machine (C:\Program Files\VAC is a good choice) and then double-click on the setup.exe file. It’s then just a matter of following the instructions. Note that because VAC4.13 is basically a driver rather than an application, you won’t see any icon for it on your desktop after it has been installed. Instead, you will see a ‘Virtual Audio Cable’ folder in the ‘All Programs’ list and if you select this you’ll see a number of items including a Control Panel icon. This allows you to do all kinds of highly technical set-up adjustments but you really don’t need to worry about this if you’re just going to use VAC as a single virtual audio cable between SDR# and DREAM. It automatically sets itself up as ‘Virtual Audio Cable 1’ during the installation. If you want to confirm that it has done this, just go into Start -> Control Panel -> Hardware and Sound -> Device Manager -> Sound, Video and Game Controllers, and you should see ‘Virtual Audio Cable 1’ listed. Next, it’s a good idea to plug the USB cable from SiDRADIO into the USB port you’re using for it and then fire up SDR#. Make sure that you have setup SDR# to work with the RTL-SDR/ USB device and that it’s set initially for AM reception. Then click on the Play button at upper left. You should find that when you tune into an AM signal, you’ll hear its audio coming from the PC speakers as usual. Now click on the Stop button at upper left and look down SDR#’s lefthand control panel until you find the Audio control area. Here you’ll find the Output label, with a text box to its right showing your current audio controller. When you click on the down arrow at the righthand end of this text box, you should see another option with a name like ‘Virtual Cable 1’ or ‘[MME] Virtual Cable 1’ – see Fig.2. Click on Play again and you’ll see SDR# begin scanning once again. There will be no sound coming from the PC’s speakers because the audio output from SDR# will now be going into VAC’s virtual audio cable. So the silence shows that VAC has been installed correctly and is ready to do its job. siliconchip.com.au Fig.5: you'll need to fire up SDR# before running the DREAM application to demodulate tuned DRM30 signals. This screen grab shows the two applications running on a Windows 7 desktop. Just before you move on to install DREAM, click on SDR#’s Stop button and then change its audio output back to the usual ‘sound card’ setting for SDR reception. This makes it easier to search for DRM30 signals, after DREAM has been installed. Also click on the USB radio button in the Radio area at the top of SDR#’s lefthand control panel, so that it becomes SDR#’s demodulation mode (you can see the button with a green dot in Fig.2). Next, move down to the text box just under the label ‘Filter bandwidth’ (in about the centre of the Radio area), click in this text box and type in 10000, as shown in Fig.2 as well. You will now have set up SDR# for DRM30 reception, apart from switching its audio output over to VAC and DREAM once you have found and tuned in a DRM30 signal. That will be easy to do later, so for the present just close down SDR# by clicking on its red Exit button at top right. Getting & installing DREAM Now you can download and install DREAM, the second item of software needed for DRM30 reception. Doing this is more complicated because for copyright reasons, one component of DREAM cannot be included in or with it before downloading. It must be downloaded separately from a difsiliconchip.com.au ferent website and then added to the same folder as the rest of DREAM. This ‘secret’ component is faad2_ drm.dll, which as the name suggests is an application extension. It’s a very important one in fact, because it’s the MPEG-4 HE-AAC v2 codec which DREAM needs to decode DRM signals. The first step is to download the rest of DREAM, from the www.sourceforge.net URL shown in the Useful Links panel. You’ll find the latest version of it there as a zip file, with a name like Dream-1.17-qt4.zip and a file size of about 12.8MB (ie, that’s the name and size of the latest version at the time of writing). Download the zip file and unzip it into a suitable folder on the same PC you’re using for SDR#. I suggest you create a folder with the name like C:\ Program Files\Dream\, for example. You’ll probably need administrator privileges to do this, especially with Windows 7. Once all of the files have been unzipped into this folder, you’ll find the DREAM app itself in the folder as Dream.exe. You might want to create a shortcut icon on your desktop, with this exe file as its target. You’ll then be able to launch DREAM at any time, simply by clicking on the shortcut. Before you do this, you need to download that all-important faad2_ drm.dll file containing the HE-AAC2 v2 codec in pre-compiled form. In order to download this file you’ll need to go to the URL shown in the Useful Links box – the one at the website www.mega.co.nz with the weird and wonderful 53-character codeword. If you go directly to this website you’ll need to type this full codeword into your browser very carefully (with no spaces) or it won’t work and you won’t be able to download the file. There is another way to get to it though, if you find it just too hard to type it in successfully. That’s to go to the fourth URL given in the first section of our Useful Links box – the one at www.rtl_sdr.com, leading to a tutorial on using an rtl-sdr to receive DRM. If you open this tutorial (which has a lot of useful information, by the way), you’ll find on about the third page a paragraph of text about the faad2_drm.dll, and towards the end of this paragraph there’s a link called ‘this megaupload link’. If you click on this link, it’ll take you directly to the correct download page of the www. mega.co.nz website, as shown in Fig.3. You should then be able to download the faad2_drm.dll file just by clicking on the large red down arrow in the centre. Once you have downloaded the faad2_drm.dll file, it’s simply a matNovember 2013  67 Fig.6: when DREAM is started, it initially has a blank display, with a level meter to the left. ter of copying it into the folder where you have already installed DREAM (eg, C:\Program Files\Dream\). Then when you fire up DREAM, it will be able to find the HE-AAC2 V2 codec it needs for decoding DRM30 signals. So that’s the procedure for acquiring and installing the additional software needed for using your SDR set-up to receive DRM30 signals. Now we can discuss what’s involved in using it with the SiDRADIO. Receiving a DRM30 signal To paraphrase an old saying, the first step in receiving a DRM30 signal is to find one. And as noted in our general article about DRM elsewhere in this issue, DRM signals are not that easy to find at present in our region of the world. You should refer to the table shown in Fig.4 of that article and use it to guide you in searching for one of the signals at the frequency and broadcasting time shown in the table. Here are a few tips to make things easier: (1) Make sure that the LF-HF input of Fig.7: select these various menus to configure DREAM to use the demodulated DRM30 audio from SDR#. your SiDRADIO is connected to the best HF antenna you can organise – a long wire mounted as high as possible outside the house would be ideal. An active indoor loop antenna might work but then again it might not. (2) Initially, you should use SDR# with its Audio output switched to the PC’s sound card, with its demodulation mode set to USB (upper sideband) and its Filter bandwidth to 10kHz, as noted earlier. (3) When you are looking for a known DRM30 signal, set the receiving frequency of SDR# to a figure 5kHz lower than the listed frequency for that signal. That’s because the listed frequency is the centre frequency of the DRM30 signal block but in upper sideband mode we have to set SDR#’s ‘local oscillator’ to the bottom of the signal block – which is in most cases 10kHz wide. This is shown the screen grab of Fig.4, where SDR# is set to receive a DRM30 signal from NZRI centred on 15.720MHz. SDR#’s receiving frequency is 15.715MHz, as shown by the Fig.8: this screen grab shows a typical display in DREAM when a DRM30 signal in tuned. In this case, the station is RNZI and DREAM indicates that the signal has a sampling rate of 15.48kps and was encoded in mono using the AAC+ codec. The signal strength is also shown. 68  Silicon Chip larger digits just above the spectrum display window. In the centre of the spectrum display itself, you can see two vertical red cursor lines – one at the lefthand end of the DRM30 signal block corresponding to SDR#’s tuning frequency and the other in the centre of the block where I had positioned the mouse cursor to show the centre frequency just before capturing the screen grab. (4) When you have managed to find a DRM30 signal like that shown in Fig.4, use the tuning and RF gain controls of the SiDRADIO to achieve the best possible signal level – using both the spectrum analyser and waterfall displays of SDR# to guide you. The idea is to set SiDRADIO’s RF gain to about 60% and then carefully adjust its in-band tuning control until you see the noise+signal level rising as high as possible on the spectrum display. (5) Next, turn up the RF gain control until the 10kHz-wide band on the waterfall plot becomes as dense as possible, showing that the DRM30 signal is at the highest possible strength. You should end up with a display rather like that in Fig.4. At this stage, you will only be hearing a hissing sound from the speakers because the audio output from SDR# is still going ‘that-away’. So now you have found a DRM30 signal, stop SDR# temporarily while you redirect its audio output to Virtual Audio Cable 1. To do this, click on the down arrow at the end of the Output text box in SDR#’s Audio area and select ‘[MME] Virtual Cable 1’ (as shown in Fig.2). Then click SDR#’s Play button to restart it again. You will now be hearing nothing, since DREAM is not running as yet. siliconchip.com.au Next, fire up DREAM. Note that SDR# must be running before you do this and it must also be running all the time you are using DREAM, because DREAM needs SDR# to provide its demodulated DRM30 signals for decoding. You will also need SDR#’s displays to guide you in making any adjustments that may be needed to optimise DRM30 reception. So you’ll find it best to have both applications visible on your desktop, arranged as shown in Fig.5. As you can see, the SDR# display is at upper right on the screen, while DREAM’s smaller display is at lower left. Driving DREAM When you start DREAM, you’ll see a largely blank display like that shown in Fig.6, with a small level meter bar chart at centre left and a single message ‘Scanning . . .’ in blue in the centre of the black quadrant at upper left. You then need to configure DREAM to take its input signal from the VAC virtual cable, ie, use the demodulated DRM30 audio coming from SDR#. Click on the Settings menu head to get the drop-down menu shown in Fig.7, then click on the Sound Card listing at the bottom of this menu to get a flyout sub-menu offering a choice of options: Signal Input or Audio Output. Clicking on Signal Input will produce another flyout menu with three options: Device, Channel and Sample Rate. Click on Device to see a further flyout menu allowing you to choose between [default], Virtual Cable 1 or the name of your PC’s sound card. At this point, your DREAM display should be as in Fig.7, with the above chain of menus. The sound card of the PC concerned is at the bottom of the final flyout list, called ‘SoundMAX Digital Audio’. However, the centre item here is Virtual Cable 1, which is highlighted and ticked to show that it has been selected as the input device. This is the main step in setting up DREAM, although if you wish you can click on the Sample Rate item in the second-last flyout, to check that DREAM is set for an input sampling rate of 48kS/s. If not, select that rate. You can also go back to the first flyout and select Audio Output, to check that DREAM is also set up correctly to feed its own decoded digital audio out to your PC’s sound card DACs. If that’s also true, you have now set up DREAM siliconchip.com.au Fig.9: the virtual audio cable driver (VAC) must be set to transfer digital audio samples at up to the same rate as SDR#, ie, 48kS/s. That's done by starting VAC’s control panel app and checking that the figures for the ‘SR range’ (given in the summary line for Cable 1) are ‘22050..48000’. correctly so that it’s ready to roll. The small level meter display at lower left in the black quadrant of DREAM’s display should be displaying a green bar at least halfway up. If it’s not up this far, go back to SDR#’s display dialog and move the Audio Volume slider to the right a little, until the meter in DREAM does show a green bar extending up this far. Now if the DRM30 signal you’ve tuned to is strong enough, DREAM should whirr away for a few seconds and then announce that it has recognised a DRM30 signal. Its display should look like Fig.8, where the things to note are the information in the black quadrant showing that it has found an RNZI signal from New Zealand with a program in English, encoded using the AAC+ codec (AKA HE-AAC V2), in mono and with a data rate of 15.48kbps. This information is also shown more briefly in the top row of the lower half of DREAM’s display, labelled as ‘1’. The other three rows are blank because the DRM30 signal concerned only had one service at the time. Note also that green bar of the level meter at lower left of the black quadrant is about 3/4 of the way up, showing that the strength of the DRM30 signal being received is fine. Finally, note the row of three green bars just below the level meter. These show that the received signal quality is also quite good (although varying a bit, as revealed by the word ‘Varied’ in red alongside). You should also be hearing the decoded DRM30 audio via your PC’s speakers. This will be the final confirmation that your DRM30 reception set-up is working correctly. Troubleshooting But what if you were unable to get this far, for some reason? Here are some troubleshooting tips: You need to make sure that SDR# is set for sampling at 48kS/s. You can Useful Links (1) For more information about DRM and decoding it via RTL-SDR: www.drm.org/wp-content/uploads/2013/09/DRM-guide-artwork-9-2013-1.pdf en.wikipedia.org/wiki/Digital_Radio_Mondiale en.wikipedia.org/wiki/High-Efficiency_Advanced_Audio_Coding www.rtl-sdr.com/tutorial-drm-radio-using-rtl-sdr/ sourceforge.net/apps/mediawiki/drm/index.php?title=RTL2832U_Guidance (2) Websites for downloading Virtual Audio Cable (VAC): software.muzychenko.net/vac.htm download.cnet.com/Virtual_Audio_Cable (3) Website for downloading DREAM, the DRM Receiver application: sourceforge.net/projects/drm/files/dream/ (4) Website for downloading precompiled faad2_drm.dll: https://mega.co.nz/#!m5RUHIDQ!SqcGUBSGMFSTAm09XX78RDYRoIJW0T 545QQRJ_dFuE November 2013  69 What About Direct Sampling? A few readers have contacted us since we described the HF Up-Converter for DVB-T dongles in the June 2013 issue, asking us about an alternative ‘direct sampling’ approach to achieving LF-HF reception. Details of this approach have appeared on a number of websites, with a particularly informative one to be found using this URL: www.rtl-sdr.com/rtl-sdr-directsampling-mode/ Basically, the direct sampling approach involves surgery on the PCB inside the dongle – see Fig.12: (1) Break one of the two differential digital signal paths linking the outputs of the E4000/FC0013/R820T tuner IC and the inputs of the RTL2832U COFDM demodulator IC. (2) Connect an HF antenna to either one or both of the freed differential inputs of the RTL2832U, either directly or via a suitable HF balun. This allows the RTL2832U to sample the HF signals from the antenna directly, without needing an up-converter to shift them up into the VHF tuning range of the tuner IC. Apart from the need to perform quite delicate surgery on the very small PCB of most DVB-T dongles, this approach is relatively straightforward. That’s because the developers of SDR# made provision for it to accept direct sampling from either the ‘I branch’ or the ‘Q branch’ inputs of the RTL2832U chip, instead of the usual ‘quadrature sampling’ mode used when the tuner IC is still in use. Note: if you open SDR#’s Configure dialog for the RTL-SDR/USB dongle in use and click on the down arrow at the end of the text box below the Sampling Mode label, you’ll find these other sampling options. So if you don’t mind the challenge of microsurgery on a tiny DVB-T dongle PCB, this direct sampling approach might be worth a try. Here’s how to do it: The differential inputs of the RTL2832U chip use pins 1 & 2 (for the I+ and I- inputs) and pins 4 & 5 (for the Q+ and Q- inputs). In most DVB-T dongles, these pins are connected to the I+, I-, Q+ and Q- output pins of the tuner chip, via tiny SMD coupling capacitors. The easiest way to break one of these two differential links is to cut the tracks on the PCB between one pair of these coupling capacitors and the outputs of the tuner chip. For example, you can follow the tracks from pins 1 & 2 of the RTL2832U chip (the I+ and I- inputs) to find the coupling capacitors for the ‘I’ channel, and then carefully cut the tracks leading from these capacitors back to the tuner chip outputs. Alternatively, you can follow the tracks from pins 4 & 5 of the RTL2832U chip (the Q+ and Q- inputs) to find the ‘Q’ channel coupling capacitors and then cut the tracks leading from these capacitors back to the tuner chip outputs. This isn’t as easy as it might sound but it turns out to be easier and safer than trying to remove one pair of capacitors from the PCB – because trying to remove them usually results in lifting their solder pads as well, together with some of the tracks leading to them. It’s also difficult trying to solder wires directly to pins 1 & 2 (or 4 & 5) of the RTL2832U. The pins on this chip are very closely spaced, making bridging between them almost inevitable. So our suggestion is to cut the tracks between the coupling capacitors and the tuner chip, but leave the coupling capacitors in place because it’s easier to solder wires to the RTL2832U ends of the capacitors than to try soldering check this simply by looking closely at the Sample Rate text box in the Audio area of SDR#’s lefthand control panel, where you should be able to see 48000 sample/sec displayed in light grey. If not, stop SDR# and exit from it, and then use a text editor application like Notepad to open the file SDRSharp.exe.Config, which you’ll find in the C:\Program Files\SDR# folder on your hard disk (or whichever folder you’ve used to install SDR#). If you look down through this file, you’ll see a series of lines starting with <add key= , followed by a text string in quotes and then a parameter value. Find the line which starts like this: <add key="minOutputSampleRate" This line should continue and end like this: value="48000" /> If it doesn’t, edit the line so that it looks exactly like this: <add key="minOutputSampleRate" value="48000" /> Make sure you copy this line exactly, noting where the spaces are and where there are no spaces. Also make sure the line begins with the ‘<’ character and ends with the ‘/>’ combination and save the file again, Now when you start up SDR#, it should display 48000 sample/sec in its Audio Sample Rate text box. You also need to make sure that the virtual audio cable driver (VAC) is set for transferring digital audio samples at up to the same rate of 48kS/s. You can do this by starting up VAC’s control panel app and checking that the figures for the ‘SR range’ given in the summary line for Cable 1 (in the lower dialog box – see Fig.9) are ‘22050..48000’. If the maximum figure is not 48000, you can change it by typing this number into the second text box in the top row of the ‘Cable parameters’ area at upper right. If you’re sure that SDR#, VAC and DREAM can communicate at the sam- 70  Silicon Chip BALUN TO HF ANTENNA SOLDER WIRES FROM BALUN TO ENDS OF COUPLING CAPS ON RTL2832U SIDE I+ VHF ANTENNA INPUT TUNER CHIP I– (E4000, FC0013 OR R820T) Q+ X X Q– 1 2 4 5 USB PLUG I+ I– Q+ Q– REALTEK RTL2832U DEMODULATOR CUT TRACKS BETWEEN COUPLING CAPACITORS & TUNER CHIP PINS Fig.12: here's how to modify a DVB-T dongle for direct sampling of LF-HF signals. You have to cut two signal lines from the tuner chip & connect an HF antenna to the freed differential inputs of the demodulator. siliconchip.com.au them to the pins of the chip itself. Luckily, even if you damage the PCB trying to make this mod to the ‘I channel’ (pins 1 & 2) inputs of the RTL2832U chip, all is not lost because you can try again with the ‘Q channel’ inputs (pins 4 & 5). And SDR# is just as happy doing direct sampling via the Q channel/branch as it is doing it via the I channel/branch. But is this direct sampling approach worth doing? To find out, I modified one of our dongles and tried it out. The results were quite good for AM reception on the LF and MF bands, with the antenna coupled into the RTL2832U chip directly via a small balun. I then tried using the front end of the SiDRADIO to provide some RF gain and preselection ahead of the RTL2832U and checked this hybrid approach on the shortwave bands. The results were not too bad up to about 9MHz but there were all kinds of ‘birdies’ and other interference when tuning to higher frequencies. My impression was that there was quite a bit of cross-modulation from the 28.8MHz clock oscillator in the dongle, causing some of these problems. So overall, I can recommend the direct sampling approach if you just want to use a spare DVB-T dongle for SDR reception of the local AM radio signals. But for more serious reception on the shortwave bands, our Up-Converter or SiDRADIO would be far superior. And don’t forget that once you’ve operated on a dongle to try out the direct sampling approach, it would probably be almost impossible to convert it back for VHF-UHF reception using the tuner chip. pling rate of 48kHz, yet you still don’t seem to be able to receive a DRM30 signal properly, the most likely cause is that you are not able to receive DRM30 signals at a high enough level to allow reliable decoding. If this is what is happening, look carefully at the upper black quadrant of DREAM’s display – and in particular at the signal level meter and the three rectangular ‘LEDs’ just below it. You’ll probably see the green signal level bar only extending up by less than half the range and one or more of the three signal quality indicators either dark or red – indicating that DREAM simply doesn’t have enough to work on. siliconchip.com.au Fig.10: if the System Evaluation dialog displays 'No audio decoding' possible, then signal strength & quality is the likely problem (ie, the signal strength is inadequate for reliable decoding). Fig.11: the System Evaluation dialog can also display the decoded constellation diagrams for the received DRM30 signal’s FAC, SDC and MSC data channels. To explore this further, click on the View menu heading at the top of DREAM’s display dialog and then click on the 'Evaluation Dialog . . .' line in the drop-down menu. This will cause a System Evaluation dialog to be displayed, like the one shown in Fig.10. If the white window on the right is virtually empty and has the legend ‘No audio decoding possible’, then signal strength and quality is almost certainly your problem. You can also click on the FAC/SDC/ MSC line in the Constellation section of the Chart Selector list at centre left of the System Evaluation dialog. You’ll then see DREAM’s display of the decoded constellation diagrams for the received DRM30 signal’s FAC, SDC and MSC data channels, plus a lot of other data as shown in Fig.11. Above the constellation diagram, you’ll see a vertical column of six display ‘LEDs’, each with its own label. Basically, you won’t achieve good decoding of a DRM30 signal unless all six of these indicators are GREEN. Even if the lowest five indicators are green and only the top indicator labelled ‘MSC CRC:’ is red (as shown in Fig.11), you still won’t get good decoding and SC reception. November 2013  71