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Got a USB TV dongle? Now you can have a . . . By JIM ROWE SoftwareDefined Radio Back in June 2012, we reviewed the WiNRADIO Excalibur softwaredefined radio (SDR), an impressive communications radio in a tiny diecast metal box which connects to a PC. Now you can get an SDR covering a frequency range from around 50MHz (or lower) up to 2200MHz for just the price of a USB DVB-T dongle – peanuts! L AST MONTH, we showed you how to use a cheap USB DVB-T dongle to watch TV or listen to digital radio on your PC. But they can do even more interesting stuff. Using the right software, one of these can turn your PC into a wideband VHF/UHF multimode SDR – a software-defined radio receiver. And yes, it also has its own spectrum display. Don’t get us wrong – a USB DVB-T dongle cum software-defined radio is not going to give you the same great performance as a WiNRADIO Excalibur. However, it is going to give you a very wideband receiver with many of the facilities of a fully-fledged communications receiver. So let’s look at the background. Back in the late 1970s, firms in the USA and Germany began developing fully digital radio transmitters and Table 1: Common DVB-T Dongle Tuner Chips & Their Frequency Ranges Tuner Chip Elonics E4000 Frequency Range DVB-T dongle model in which chip is found 52 – 2200MHz* EzCAP EzTV668 DVB-T/FM/DAB, many current 'no name' devices Rafael Micro R820T 24 – 1766MHz ? (not known – but may be in many future dongles) Fitipower FC0013 22 – 1100MHz EzCAP EzTV645 DVB-T/FM/DAB, Kaiser Baas KBA010008 TV Stick Fitipower FC0012 22 – 948MHz Many of the earlier DVB-T dongles * With a gap from 1100MHz to 1250MHz (approx) 12  Silicon Chip NOTE: Elonics may have ceased manufacture receivers for use by the military and space industries. At first, these were classified but gradually the results of this work started to percolate through into commercial “software-defined” radio receivers and transmitters, in which many of the functions previously performed by dedicated hardware modules were performed by complex software or firmware. The advantages were obvious: lower cost, lower weight and much greater functional flexibility. It soon became clear that softwaredefined radio or “SDR” was likely to become just another kind of PC application. This process received a dramatic boost in 2009 when Antti Palosaari, a Linux software developer in Finland, made an interesting discovery when siliconchip.com.au he was working on Linux drivers and routines to allow DTV reception using one of the DVB-T dongles which had just started to appear. Delving into the firmware code inside the Realtek RTL2831U demodulator chip that was used in most of the early dongles, he found that it had an undocumented “radio” mode, presumably intended to allow FM reception as well as DTV reception. In this mode, the chip would output a stream of 8-bit I/Q (inphase/quadrature) digital samples via the USB port, at rates of up to 2MS/s (megasamples per second). Antti Palosaari realised that this would allow other kinds of demodulation to be performed by software in the PC. This was confirmed when almost all later DVB-T dongles came with the higher-performance Realtek RTL2832U demodulator chip with the same in-built “radio” mode as its predecessor. So Palosaari got together with other software developers from Osmocom (the Open Source Mobile Communications group) and they soon developed suitable drivers and software for both Linux and Windows. Now anyone can have a wideband VHF/UHF SDR, using a low cost DVB-T dongle and a PC or laptop. So let’s take a look at what a typical SDR/USB dongle set-up can do. Same hardware as before Just as with DTV and DAB+ reception, the only hardware you’ll need for using your PC as an SDR is the PC itself (with a free USB 2.0 port), a low-cost DVB-T dongle and a decent outdoor VHF/UHF antenna. Everything else is handled by software. Which type of DVB-T dongle is best suited for use in an SDR? That depends on what range of frequencies you want to receive, because the main difference between most of the currently available dongles is their tuner chip, as mentioned last month. And the main difference between these tuner chips is their tuning range – see Table 1. So if you’re mainly interested in scanning frequencies up to 1100MHz or so, almost any of the dongles will likely do the job. But if you want to tune much higher frequencies, you’re going to need a dongle with either the Elonics E4000 or the Rafael R820T tuner chip inside – like the EzTV668 or many of the current “no name” dongles. siliconchip.com.au Fig.1: an omnidirectional antenna like this Icom VHF/ UHF discone is ideal for use with an SDR. Note that although the Elonics E4000 tuner chip covers the widest frequency range, it also has a gap between about 1100MHz and 1250MHz where it has no coverage. So if you are particularly interested in receiving signals in this region, you’ll want to search the online market for a dongle with the Rafael R820T tuner chip inside. We’re not aware of any just yet but they’re probably around on the web if you look hard enough. Remember too that dongles with the E4000 tuner chip in them may not be available for much longer, as Elonics has apparently gone out of business. So when the dongle makers use up their stocks of the E4000, many of them will have to swap over to the R820T anyway. How about the antenna? Well, as we noted last month, the tiny “whip” antenna that comes with many DVB-T dongles is pretty useless even for DTV and DAB+ reception – and it’s even more useless for SDR reception. So you’re really going to need a decent outdoor VHF/UHF antenna. For your initial SDR experiments, you’ll probably get moderately encouraging results by using a standard TV antenna. However, as these are gener- ally quite directional, they’ll tend to be very insensitive to signals coming from directions other than directly in front. In practice, you’ll get much better results from an omnidirectional VHF/ UHF antenna like a “ground plane” or (preferably) a “discone”. A discone is a wideband omnidirectional antenna with two main elements: a horizontal disc on the top and a conical shape below it (rather like an inverted ice-cream cone). Both the disc and cone elements may be made from either sheet metal or an array of stout wire “spokes”. Sheet metal elements are more common in discones intended for use at frequencies above 1GHz, while “spoke” elements are generally used for discones intended for use at lower frequencies. By the way, the discone antenna was invented and patented by US engineer Armig G. Kandoian in the mid 1940s. Some discones intended for use down into the lower VHF region have an additional vertical whip element at the top, to effectively convert the antenna into a half-wave vertical dipole at the lower frequencies. This is the case with the discone shown in Fig.1, which is a wideband VHF/ UHF antenna made by Icom about 15 May 2013  13 The SDR# Application & Its Features SDR# is an easy to use software application designed to turn almost any PC into a powerful SDR (software defined radio), using either a DVB-T dongle (the hardware “front end”) or other devices. Here are some of its salient features: (1) RF performance, frequency accuracy: the RF performance basically depends on the chips used in the DVB-T dongle used with SDR#. A typical dongle fitted with the Elonics E4000 tuner chip can tune from 52-1100MHz and 1250-2200MHz, with a sensitivity of approximately 1.5µV for 12dB of quieting at frequencies up to about 180MHz, rising to about 20µV for the same degree of quieting at 990MHz. The SDR# software used with the dongle provides a Frequency Correction feature, whereby you can correct for any frequency error in the DVB-T dongle. In addition, there is a Frequency Shift feature, allowing you to display the correct frequencies even when you have an up-converter connected ahead of the dongle. (2) Demodulation modes: AM (amplitude modulation), NFM (narrow frequency modulation), WFM (wide frequency modulation), LSB (lower sideband), USB (upper sideband), DSB (double sideband), CW-L (carrier wave with BFO on low side) and CW-U (carrier wave with BFO on high side). In all these modes, the RF filter bandwidth can be adjusted over a wide range, while the filter type can be selected from a range of five (Hamming, Blackman, Blackman-Harris, Hann-Poisson or Youssef). The filter order can also be selected over a wide range. In both CW modes, the frequency separation of the software BFO can also be adjusted. There is adjustable squelch and also both linear and “hang” AGC. (3) FFT spectrum display and/or Waterfall spectrum/time display: the FFT spectrum display and Waterfall display can be selected either separately or together. The windowing function used can be selected from six choices: None, Hamming, Blackman, Blackman-Harris, Hamm-Poisson or Youssef, and the display resolution can be adjusted over a wide range by changing the block size from 512 to 4,194,304, in powers of two, with the higher resolutions requiring greater processing overhead. Good results can be achieved with the default resolution of 4096, which was used for all of the screen grabs shown in this article. years ago. It originally sold for about $100 but Icom don’t seem to sell them anymore. However, Australian firm ZCG Scalar make what they call a “Basestation Omnidirectional Broadband Discone”. Designated the B51H, this is available through their dealer network – see their website at www.zcg.com.au If you search around on eBay, you’ll find that suitable VHF/UHF discones are also available for online purchase. In particular, we found one from Mr CB Radio of Richmond, Victoria for $97.00 plus postage. Another one called the “Jetstream JTD1” was available from a couple of US suppliers (CQ Radio Supply and k1cra Radio Store) for between US$33 and US$56, with a further $50 or so for postage to Australia. There’s also information available on the web showing how to make your own discone, eg, see helix.air.net.au Another website at www.ve3sqb.com has software that works out the ele14  Silicon Chip ment dimensions for various antennas (including discone antennas). Software is crucial As with DTV and DAB+ reception, the software needed to configure a PC/ dongle combination as an SDR consists of two main components: (1) a driver which allows the PC to communicate via the USB port with the Realtek RTL2832U (or similar) demodulator chip inside the dongle and (2) the application software to allow the PC to perform all the functions of an SDR in company with the dongle hardware. The driver must be installed first. The most popular driver for a DVB-T dongle with an RTL2832U demodulator chip (when used as an SDR) is the “RTLSDR” driver (nearly all dongles use the RTL2832U). There’s even a website at rtlsdr.org which provides lots of information about it. Zadig The easiest way to install the RTL­ SDR driver is to use an open-source driver installer program called “Zadig”. Developed a couple of years ago by Pierre Batard, Zadig is currently available as version 2.0.1.160 in two forms, one for Windows XP and the other for Windows 7. Both are about 5.2MB in size and they can be downloaded (as selfinstalling exe files) from sourceforge. net/projects/libwdi/files/zadig It’s important to get the right one for the version of Windows on the PC you’ll be using for the SDR. Note that both files are compressed in a “7z” archive format, so you won’t be able to extract the exe file from the download with WinZip. Instead, they can only be extracted using 7-Zip, a compression/ extraction utility which offers a higher compression ratio. Fortunately, this too can be downloaded, either from sourceforge.net or directly from the 7-Zip developer’s website at www.7zip.org 7-Zip also comes in two forms – one for 32-bit x86 systems (ie, Windows XP) and the other for 64-bit x64 systems (eg, PCs running 64-bit versions of Windows 7). If you don’t already have 7-Zip, the first step is to download and install it. Then you can download the correct (and latest) version of Zadig, after which you can use 7-Zip to extract the Zadig.exe installer file. You then run this file to install Zadig itself. With Windows 7, you have to run the installer file as the Administrator. This is very important, as otherwise it won’t install Zadig correctly. Next, plug your DVB-T dongle into the USB 2.0 port you intend to use for the SDR. Windows will then go through its usual rigmarole, looking for what it thinks is a suitable driver for the dongle. Don’t worry if it does this though, because you’ll be using Zadig to install the correct SDR driver shortly. Now start up Zadig in the usual way. With Windows XP, you should immediately see the dialog shown in Fig.2. With Windows 7, you’ll almost certainly get a User Account Control window first. Click “Yes” to allow Windows 7 to run Zadig, to display the same start-up window. Next, click on the Options menu and you should see a drop-down menu as shown in Fig.3. Click in the blank area just to the left of “List All Devices” and the drop-down Options menu should siliconchip.com.au siliconchip.com.au May 2013  15 Fig.2: the Zadig startup window. This application is used to install the RTL-SDR driver to allow the PC to communicate with the Realtek RTL2832U demodulator. Fig.3: clicking the “Options” menu brings up this dialog after which you have to select the “List All Devices” option from the drop-down list. Fig.4: clicking the down arrow brings up the list of USB devices that Zadig has discovered. You then have to select the USB dongle entry from this list. Fig.5: the RTL2838UHIDIR entry has been selected here (for an EzTV668 dongle). You then have to click the “Reinstall Driver” button to install the correct driver. disappear. However, there will now be some text displayed in the main drop-down menu bar, probably for one of your USB devices like a mouse, keyboard or printer. Click on the down arrow at the right-hand end of this bar. You should get a drop-down list of all of the USB devices that Zadig has been able to find connected to your PC – see Fig.4. You now have to go through this list to find the DVB-T dongle that’s plugged into one of the USB ports. The only catch here is that it can be listed under various different names, depending on the dongle. Some dongles may appear as “RTL2838UHIDIR” as shown at the bottom of the list in Fig.4, while others may be shown as “Bulk-In, Interface (Interface 0)” as shown in Fig.6. Still others may appear as “RTL2832U” or similar. The main things to look for are either that “Bulk-In, Interface” label or one starting with “RTL”. When you spot the dongle in Zadig’s list, click on its entry to highlight it. Zadig should now display the dongle’s label in the main horizontal bar, as shown in Fig.5 and Fig.6. However, at this stage it either won’t be showing anything in the Driver text box or it’ll be showing whatever driver Windows installed (or tried to install) when you plugged the dongle into a USB port. 16  Silicon Chip Fig.6: this screen grab in similar to Fig.5 but in this case, after Zadig has installed the correct RTL-SDR driver for Kaiser Baas KBA010008RT dongle. Either way, you’ll probably see text entries in the smaller boxes to the right of the “USB ID” label, as shown in Figs.5 & 6. Now turn your attention to the blue rectangular button at the lower centre of the Zadig window, which will probably be displaying the text “Reinstall Driver”. If it isn’t, click on the down arrow at its right-hand end and select Reinstall Driver from the resulting drop-down list. Once the correct text is displayed, click on this button to install the correct driver for SDR. After “whirring” away for a few seconds, Zadig should display a “Successful Install” message and then you should see the correct driver name displayed in both the Driver text box and also in the box further to the right (just to the right of the green arrow). You can see the driver displayed in these boxes in Figs.5 & 6. The driver should now be installed correctly and will be called up automatically whenever your dongle is plugged into the same USB port at a later time. So if you always plug the dongle into the same port when using it for SDR, you won’t have to fire up Zadig to reinstall the driver again. Conversely, if you plug the dongle into another USB port, you’ll have to run Zadig again to reinstall the driver for that port. As a corollary to this, you will be able to use the same dongle for DVB-T and DAB+ reception simply by plugging it into a different USB port; ie, one for which Zadig hasn’t installed a driver. What’s next? Once Zadig has installed the SDR driver, exit the application in the usual manner. However, before you move on to download and install the SDR application software, it’s a good idea to go into Control Panel -> System and siliconchip.com.au Security -> Device Manager to make sure that the driver has been installed correctly. In Device Manager, scroll down to “Universal Serial Bus Devices” (see Fig.8) and click on the arrow to the left. You should now see a device entry with the same name as that previously shown in Zadig (it’s shown as “RTL2838UHIDIR” in Fig.8). This will be your dongle and if you then rightclick on this device name and select “Properties”, you should see another small window like that shown on the right in Fig.8. Click on the Driver tab in this window and you should be presented with the details of the driver that Zadig installed. As shown in Fig.8 the Driver Provider should be shown as “libusbx.org” and the Driver Version as “6.1.7600.16385” (or another number if it has been updated from the current version). If that all checks out, then Zadig has correctly installed the SDR driver for your dongle and you’re now ready to install the application software. Our first choice: SDR# If you search the web, you’ll find a number of different SDR software applications that run under Windows or Linux and are compatible with RTLSDR dongles. The most popular of these seems to be an application called SDR# or “SDRSharp”, written by a programmer in Paris by the name of Youssef Touil in collaboration with various other people around the world. SDR# is a particularly powerful and easy to use SDR application and it’s available for free. It provides an excellent way to “dip your toe” into SDR. Downloading and installing SDR# is a little tricky though, because it’s not packaged as a “single exe” or “zipped exe” file. Due to licensing and packaging considerations, it has been split into two main zip files which can be downloaded from the SDR# website – plus another zip file which must be downloaded from a different website. Here’s the downloading procedures, step by step: STEP 1: fire up your web browser and go to the SDR# homepage at www. SDRSharp.com Then click on the “Downloads” heading to go to the downloads page. Here you’ll find two main files. One will have a name like SDR# Dev or sdr-nightly, followed by a description in brackets like (Consiliconchip.com.au Coming: An Up-Converter For HF Reception As shown in Table 1, none of the tuner chips used in currently available dongles will tune down below 22MHz, while dongles with the popular E4000 tuner chip won’t go below 52MHz. So by themselves, none of these dongles are suitable for turning your PC into an SDR covering the LF/MF/HF bands (these bands include broadcast-band AM radio and various shortwave radio and amateur radio bands). So, we’re working on a small “up-converter” to connect ahead of the DVB-T dongle. This up-converter covers the frequency range from about 0-60MHz and shifts the tuned LF/MF/HF signal by 125MHz up into the VHF spectrum, well within the dongle’s tuning range. We plan to describe the up-converter in SILICON CHIP in the near future. tinuous Integration, Last Changes Rev: 1114). This is the main SDR# zip file, so download it first. That done, move down to the file named SDR# RTLSDR Plugin, which will have a similar description in brackets. This will be the latest version of the RTLSDR “plugin” for SDR# and this is the second zip file to download. STEP 2: before leaving the SDR# website, scroll further down the downloads page until you get to a section titled “Important note for RTL-SDR users”. This section provides links to various worthwhile items on SDR#, including a PDF file of a well written “SDR# User Manual” by Henry Forte. You can download this PDF file by clicking on the link www.atouk.com/ wordpress/?p=153 STEP 3: the next step is to download the third main software ingredient. This is “rtlsdr.dll”, the application extension which SDR# needs to communicate with the RTL-based dongle via the USB driver. This file can’t easily be downloaded by itself but it’s in a collection of other files which can be downloaded from the Osmocom website at http://sdr.osmocom.org/ trac/wiki/rtl-sdr/ To do this, scroll down to a section at the end called “Attachments”. In the links beneath this heading, you’ll find one with the rather odd name “RelWithDebInfo.zip”. Click on this link and you’ll end up on a page headed “rtl-sdr: RelWithDebInfo.zip”. This file can now be retrieved by clicking on the “downloading” link over on the right. Installing the software Having downloaded the three zip files, you can now proceed with the software installation for SDR#. Here’s how it’s done: STEP 1: unzip the SDR# Dev.zip (or sdrnightly.zip) file. This will have about 14 files inside, all of which should be extracted to the folder you will be installing SDR# in. For example, you could extract the files to C:\Program Files\SDR#, so it’s a good idea to create this folder before you start. Step 2: unzip the second zip file, ie, with a name like sdr-nightly-rtlsdr. zip. This will probably have five files inside, plus a folder called “config”. Extract everything to the same folder used to store the extracted the files from the first zip file. That done, check the contents of the “config” folder Fig.7: DVB-T tuner dongles can be purchased online quite cheaply. These three units all feature a 75-ohm Belling-Lee antenna socket but many other dongles come with a much smaller MCX connector. May 2013  17 downloaded, ie, RelWithDebInfo.zip. Inside this file, you’ll find two folders, one labelled “/x32” and the other “/ x64”. If you look inside the /x32 folder, you’ll see a file called rtlsdr.dll. This is the only file you need from this third zip file, so just extract this file and place it into the main SDR# folder with the others. And that’s it. Your copy of SDR# should now be fully installed and ready to run. All you need to do is go to the C:\Program Files\SDR# folder (or wherever you have installed it), right click on the filename SDRSharp. exe, and select either “Run” in Windows XP or “Run as Administrator” in Windows 7. SDR# in action Fig.8: you can verify that Zadig has correctly installed the driver by checking the entry in the Windows Device Manager. Fig.9: this is the opening window that appears when you start the SDR# program for the first time. there should only be one file with a name like sdrsharp.exe.config. Copy this file into the main SDR# folder, 18  Silicon Chip where it will over-write an existing file with the same name. Step 3: now for the third zip file you After a couple of seconds SDR# should spring into life and you’ll see a fairly large window like that shown in Fig.9. This is the opening window for the current version of SDR#, V.1.0.0.114; later versions may look a little different. At the top left of this window are two rectangular buttons, one labelled “Play” and the other with the default label “Other (Sound card)”. Clicking the down arrow to the right of this label will now bring up a drop-down device list similar to that shown in Fig.10. Click the “RTL-SDR/USB” option then click the “Configure” button. SDR# will now open a very interesting supplementary window as shown in Fig.11. This shows you the actual name of the dongle (in this case “ezcap USB 2.0 DVB-T/DAB/FM dongle”), the tuner chip it contains (here an E4000), its maximum and default sample rate (2.048MS/s) and the default sampling mode (quadrature sampling). It also gives you options for setting the AGC functions available inside the dongle (RTL AGC and/or Tuner AGC) and for adjusting the RF gain. In addition, there are options for setting a tuning offset (for when you’re using an up-converter with the dongle) and for correcting for any frequency error in the dongle’s crystal-based local oscillator. We’ll discuss these options later on. For the present, just click on the “Close” button at the bottom of this window, then take a close look at the main SDR# window. Down the lefthand side, you’ll see the SDR# control panel. This is divided into a number of functional areas, each with its own siliconchip.com.au MASSIVE LED CLEARANCE P3-II Star LED PCB Bright 2w power LEDs mounted on a 20mm star pcb for easy connection. Amber AS2182 Blue BS2182 Green GS2182 Red RS2182 EACH: Warm White NS2182 $ 90 Cool White WS2182 +GST 1 P4 Power 4w LEDs High Power LEDs in various colours up to 4w. Blue B42180 Green G42180 Red R42180 Warm White N42180 EACH: Natural White S42180 $ 60 Cool White W42180 +GST 1 Solder Like a Professional Channel Lighting Modules Thermaltronics Soldering Station 3 LED – 41lm min 21H0007 4 LED – 55lm min 21H0008 EACH: EACH: 1 $ 50 $ 98 +GST +GST 1 P7 Power LED Final Stocks As seen in Silicon Chip in Feb ’11, these LEDs are very bright. 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CT-FRGP300 EACH: $ High Brightness 24V LED Strips – Made in Australia These are ideal for under bench lighting. They deliver approx. 400lms/strip and consume just 5.5w. Available in warm and cool white. Length is 400mm 3000K STRIP-400/24V/16/3000K 3500K STRIP-400/24V/16/3500K 5600K STRIP-400/24V/15/5600K OEM enquiries also welcome ChemTools Acrylic Conformal Coating With UV Trace Easy to apply and gives a tough, high gloss finish, resistant to moisture and fungal growth. Chemtools Acrylic UV+ is your best protection against moisture dust and chemicals. Contains a UV trace for easy inspection under a UV light source. Available in various sizes. 400ml Aerosol 1 Litre CT-ACC1LT CT-ACC400 EACH: EACH: $ 18 50 895 +GST 18 $ +GST www.rmsparts.com.au siliconchip.com.au 445 $ +GST EACH: $ Intended for serious applications and is the ideal tool for production line or high volume assembly. Utilising induction heating (Curie Heat Technology), this iron will deliver heat on demand, making the soldering process both easier and faster. These modules are ideal for sign illumination. 12v Operation 95 +GST EACH: $ 45 +GST Unit 3, 61-63 Steel St Capalaba, Qld, 4157 Phone - (07) 3390 3302 Fax - (07) 3390 3329 May 2013  19 sales<at>rmsparts.com.au Fig.10: the “Other (Sound card)” dropdown list. Choose the “RTL-SDR/USB” option, then click “Configure”. Fig.12: SDR# showing a typical spectrum display. In this case, the unit has been tuned to an AM signal on 118.550500MHz in the aeronautical band (the Sydney Airport Terminal Information signal). Fig.13: the result when SDR# was tuned to 865.017MHz in the UHF fixed/mobile communications band. The signal peak is a narrow-band FM (NFM) signal coming from a tourist guide on the Sydney Harbour Bridge. Fig.11: the RTL-SDR Controller dialog. It shows the name of the dongle, the tuner chip (here an E4000), its maximum and default sample rate (2.048MS/s) and the default sampling mode (quadrature sampling). There are also options for AGC and RF gain. heading, ie, Radio, Audio, AGC, FFT Display and finally two area headings at the bottom for SDR# plugins. Within each area you’ll find various control buttons allowing you to select a variety of functions and modes. For example, the eight small buttons at the top of the Radio section allow you to select the demodulation mode you want to use (NFM, AM, LSB, USB, WFM, DSB, CW-L or CW-U). Most of the other controls are fairly intuitive, like the AF Gain slider at the top of the 20  Silicon Chip Audio section. You simply drag this slider one way or the other to decrease or increase the volume. you need to set the display to (0.)136.912.500. Tuning a frequency Just below the main frequency display is SDR#’s frequency/spectrum display window, which is probably its most impressive feature. This gives a continuous display of the spectrum in the vicinity of the tuning frequency you’ve set, with signal amplitude plotted vertically against frequency which is along the horizontal axis. This makes it particularly easy to spot the peaks or “bumps” which correspond to any signals in that part of the spectrum. If the frequency you want is actually away from the current tuning frequency, you can simply drag the tuning cursor (the vertical red line in the centre) over to the signal peak and drop it there. By the way, if there are a lot of signals visible, all jumbled together in the spectrum display, you can zoom in to a smaller section of the spectrum display simply by dragging up the “Zoom” slider on the right of this In the centre at the top of the main SDR# window, you’ll see the label “VFO” followed by a string of 10 large numerals. At this stage, these will probably all be zeroes and with all but the rightmost digit “greyed out”. This is SDR#’s main tuning frequency display and it’s also where you can directly enter the frequency you want to receive. Entering the frequency you want is easy: just move the mouse cursor over either the top half or the bottom half of any of the digits, which will cause a square of colour shading to appear behind that half of the digit (blue for the bottom half, or pink for the top half). Then if you left click on that coloured square, the digit will either increment or decrement to change the tuning frequency. It reads directly in Hertz, so to tune your SDR to say 136.9125MHz Frequency/spectrum display siliconchip.com.au window. There are other handy features too, which we’ll look at shortly. For the present though, let’s look briefly at one big feature of SDR# that we haven’t yet mentioned: its “waterfall plot” display window. This is just below the spectrum display window at lower right. Although this window is almost totally black in Fig.9 apart from a “rainbow strip” at far right, when SDR# is receiving it displays a time plot of the visible signals in the spectrum display window. This lets you see which ones are varying with modulation or are appearing in short bursts (ie, with gaps in the signal). You can adjust the colour contrast within this window using the “Contrast” slider at centre right and you can vary the time period represented by the waterfall plot using the “Speed” slider below it. Fig.14: this screen grab shows the result when we set SDR# to receive the GPS “L1” signal frequency at 1.575427GHz. There was indeed a small signal peak at that frequency but we were unable to demodulate the signal because SDR# doesn’t have an option to demodulate CDMA spread spectrum signals. Receiving a signal OK, let’s use it to receive a signal. There are really only three steps involved: (1) enter the frequency of the signal you want to receive by clicking on the appropriate digits in the top display; (2) select the modulation mode (eg, AM, WFM, LSB etc) by clicking the corresponding radio button in the Radio section at top left; and (3) click on the “Play” button just above the Radio heading, at top left. Within a fraction of a second, you should see a spectrum display like the one shown in Fig.12. In this case, the unit has been tuned to an AM signal on 118.550500MHz in the aeronautical band (it’s actually the Sydney Airport Terminal Information signal). The display has been zoomed in a little and is showing the spectrum between about 118MHz and 118.66MHz, with the peak for the signal being received in Fig.15: the frequency error in an EzTV668 dongle has been corrected here, in this case using the signal from ABC Classic FM in Sydney, on 92.900MHz. The frequency correction applied was -63ppm (parts per million). the centre (bisected by the red tuning cursor line). Looking closely at Fig.12, you’ll also see a light grey band straddling the signal peak and the tuning cursor. This shows another of SDR#’s handy features – it can graphically display the software filter bandwidth currently in use. If you change the filter bandwidth using the text box over in the Radio controls area, you’ll see the grey band change width. But that’s not all; you can also change the filter bandwidth by hovering the mouse over one side of the grey band until the cursor changes into a double-ended horizontal arrow. When it does, you can then click and drag the edge of the band one way or the other, to change the filter bandwidth. What if you do find a signal peak but the audio output is badly garbled (even when you tune accurately to the centre of the peak)? This indicates that it’s not using the type of modulation you’ve Australia’s Lowest Price Oscilloscopes! STOP PR Siglent Arbitr ESS!! ar Generators no y Waveform Siglent is one of the world’s highest volume oscilloscope manufacturers. High volume manufacture means GREAT prices. See our ww available. ebsite. Prices start at just $295.00+GST for the 25 MHz wide-screen model. Backed by a 3-year parts-and-labour warranty, we are sure these are the best value oscilloscopes you’ll find! 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If you like, you can think of this display as the SDR’s “band switching” control, while dragging the cursor in the spectrum display window is its “fine tuning” control. Two more screen grabs which should make the impressive capabilities of SDR# a little clearer are shown in Figs.13 & 14. Fig.13 shows the SDR# tuned to 865.017MHz in the UHF fixed/mobile communications band. The signal peak turned out to be a narrow-band FM (NFM) signal coming from a tourist guide up on the Sydney Harbour Bridge (he was explaining the history of the bridge and its surroundings)! Fig.14 shows the result when we set the SDR# to receive the GPS “L1” signal frequency at 1.575427GHz. There was indeed a small signal peak at that frequency but its small size is not surprising since we were only using the wideband discone antenna shown in Fig.1. In any case, we were unable to demodulate this signal because SDR# doesn’t have an option to demodulate CDMA spread-spectrum signals. Instead, all we could hear was a faint hum when the “AM” demodulation mode was selected. SDR# is also unable to demodulate DAB+ digital (COFDM) signals (perhaps this will be added in a future update). However, if you do want to listen to DAB+ radio, it’s just a matter of plugging the dongle into a different USB port and firing up a DVB-T/DAB+ application. Frequency error correction Fig.17: the spectrum and waterfall displays for three FM stations between about 102.5MHz and 104.1MHz. set SDR# to receive. That’s fixed by clicking on the other mode buttons in the Radio area until the signal becomes clear. When that happens, you have the correct receiving mode. As mentioned before, you can change the tuning frequency by clicking and dragging the red tuning cursor line in the spectrum display window. When 22  Silicon Chip you do this, you’ll see the main frequency display at the top changing as you drag the cursor. In addition, the frequency “dial markings” along the bottom of the spectrum display will also slide along. If you want to shift the tuning frequency a long way from your current setting, it’s much easier to click on the At this stage, there’s one aspect of the DVB-T dongle plus SDR# combination that we haven’t considered: its tuning accuracy. Inside virtually all currently available DVB-T dongles is a 28.8MHz crystal oscillator. This is used as a clock generator and frequency reference by both the tuner and demodulator chips. This means that the basic tuning accuracy of the dongle (and as a result our SDR) depends on the accuracy of this crystal oscillator. Not surprisingly, most low-cost dongles use a fairly lowcost crystal and its exact frequency can vary over quite a wide range. To overcome this problem, Youssef Touil and his colleagues provided SDR# with an elegant way of compensating for this “dongle tuning error”. This was done by building in a method siliconchip.com.au Helping to put you in Control Control Equipment RoboClaw DC Motor Driver Bidirectional control of 2 brushed DC motors with 2 motor channels. 6 to 34 VDC powered. 30 A continuous outputs. Configurable via pushbuttons. POL-1494 $115+GST pcDuino-Dev Board Fast, mini PC comes with Arduino-style peripheral headers. HDMI video output. RJ45 & Ethernet connection. Linux3.0 + Ubuntu12.10 supported. 1 GHz ARM Cortex A8 CPU SFA-110 $69.95+GST Fig.18: the waterfall display for several narrow-band FM (NFM) signals from Sydney airport (centre) plus various other digital signals. to allow SDR# to automatically correct its frequency calculations by a known factor (which will be different for each dongle). This may sound complicated but it’s really quite easy. All you have to do is select a signal whose carrier frequency is accurately known and then set SDR# to tune to that frequency. Then when you click on the “Play” button, you should see the carrier peak for this signal somewhere near the centre of the spectrum display. The next step is to click on the “Configure” button to call up the RTL-SDR Controller window and then turn your attention to the “Frequency correction (ppm)” text box with its up/down arrows. It’s then just a matter of clicking on one arrow or the other to move the signal peak so that it’s centred on the correct tuning frequency. If that still sounds complicated, take a look at Fig.15. This screen grab was taken after using the above technique to correct the frequency error in an EzTV668 dongle, in this case using the signal from ABC Classic FM in Sydney, on 92.900MHz. As shown, the carrier signal peak has been moved right into the centre of the spectrum display, so that it straddles the 92.900 graticule line. And, as can be seen in the RTL-SDR Controller siliconchip.com.au dialog box, this was achieved by getting SDR# to apply a frequency correction of -63ppm (parts per million). This correction process only has to be done once for each dongle, by the way. Of the other three dongles we tested, one required a frequency correction of -115ppm and another a correction of +20ppm. The remaining “no-name” dongle required no correction at all; it was spot on, probably by sheer good luck. Give it a go So that’s a quick run through the main features of SDR# and how easily it can be used to convert your PC into an SDR and wideband VHF/UHF spectrum scanner. It’s a bit of a rigmarole to download and install the special RTL-SDR driver and then SDR# itself but once you’ve done that, the set-up is remarkably flexible and easy to use. The only small “glitch” we’ve encountered so far is that sometimes when exploring the VHF or UHF bands, there’s a spurious signal peak in the centre of the spectrum display. 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