This summer I’ve been enjoying a new receiver which has terribly cheaply (for just 16.82€, or $19.20!!!!) joined the rest of my radio material. It is an ezcap ezTV645 DVB-T USB dongle and yes, you’ve read well, it is nothing more than… an USB dongle normally used to watch DVB-T TV broadcasts (DVB-T is an European standard for digital TV) in a computer!!! This highly performing device (specially when one considers its price) is my very first SDR (Software Defined Radio) receiver and has allowed me to have my very first succesful experiences in the SDR world!
It seems that USB DVB-T dongles work according to the same principle with which specific SDR USB dongles (the FUNcube Dongle being the only example) work. They use a tuner and an A/D (analog to digital) converter, which samples the output signal of the tuner, converts it to digital and sends it to the computer via the USB port. There, in the computer, a specific software takes this signal and carries out the demodulation task.
(More on SDR will be explained in a future entry; but let me only say that the advantage of SDR equipment is precisely this: to reduce the amount of physical electronic components to a minimum expression, as most of the work is carried out through software and not through “hardware” like “normal” receivers or transceivers).
Well, so what happens is that those (and for the moment, only those) DVB-T Digital TV dongles which contain both the Realtek RTL2832U A/D chipset (which gives this practice of SDR the name of RTL-SDR) and either the Elonics E4000 or the Fitipower FC0012, FC0013 or FC2580 tuners, through the use of special drivers, can be made to work as SDR receivers so as to listen to almost any kind of radio transmission in a vast (very, very vast…) frequency range.
The tuner which provides a wider frequency coverage is the E4000, from approx. 53 MHz to 2200 MHz, with a gap between, approx., 1113 MHz and 1244 MHz. The Fitipower tuners’ range is not as large, but they have an advantage in that they can receive lower frequencies. Also, and the same way it happens with the FUNcube Dongle, an external frequency upconverter can be connected between the antenna and the dongle so that all signals in frequencies below the dongles’ coverage, in bands such as HF and lower (in fact, as low as DC! :D ) are brought into the range of the dongles and can be received with them! Anyway, and using an upconverter or not (and like it happens with all SDRs), all kinds of radio signals can be received: voice (SSB, DSB, AM, FM narrow and wide), CW, even digital transmissions (such as GPS, ADS-B -which is used by aircraft transponders-, POCSAG; and ham digital modes such as APRS/Packet, D-Star, PSK, RTTY…) can be decoded using the proper software. Add to this that it is possible to display, in the SDR software, an in-screen reception spectrum with a bandwidth as large as 3.2 MHz (selecting a sample rate of 3.2 MSPS -Mega Samples Per Second-) and we have an astounding device!!!
A list of RTL-SDR compatible dongles can be found here.
At the beginning of the SDR experiments with these devices, they were used (in Windows) with known SDR softwares such as Winrad, HDSDR, or WRplus, through an external DLL controller, named ExtIO (which can be found here: http://wiki.spench.net/wiki/ExtIO_USRP). In Linux, the GNU Radio or gqrx softwares can also be used.
Recently, a new SDR program for Windows has appeared which adds a native support for RTL2832U-based DVB-T dongles. Its name is SDR# (read SDR Sharp) and it avoids the use of the ExtIO DLL which was pretty troublesome, while offering an excellent performance, and a lot of new functions (such as the demodulation of WFM -Wideband FM; used by the common commercial broadcast stations in VHF- in stereo!!!). It is a new software which is in constant development and including new functionalities, so be sure to check regularly its website (www.sdrsharp.com) for the latest released version. A good practice is to regularly download the newest version from here: http://sdrsharp.com/downloads/sdr-nightly.zip. To carry out the installation of SDR#, and of the driver which transforms the DVB-T dongle into a SDR receiver, detailed instructions can be found here.
Well, so focusing in my experience with RTL-SDR, I’ll say that my specific unit of dongle is, as I’ve already mentioned, an ezcap ezTV645, which contains the RTL2832U chipset and the FC0013 tuner. I bought it for just 16.82€ ($19.20) at dealextreme.com (http://www.dealextreme.com/p/mini-dvb-t-digital-tv-usb-2-0-dongle-with-fm-dab-remote-controller-92096?item=1). And although a small whip antena in a small magmount is supplied with the dongle, I quickly realized that it would provide a very poor reception to me (if I could receive anything with it), so I quickly discarded it. Instead, and to be able to use this dongle with any of the antennas I also use with my IC-R5 scanner (which connect to it through standard ham radio connectors: male SMA or male PL -with a PL-SMA adapter-) I homebrewed a simple antenna connector adapter, which is nothing more than a very short pigtail of RG-58 coaxial cable, with an European TV (“Belling-Lee”, IEC 169-2, or PAL) male connector in one end, and a female PL connector (or SO-239) in the other end. Also, I needed to perform minor surgery to the innards of the dongle. It happens that ezcap ezTV dongles are not supplied with an ESD (ElectroStatic Discharge) protection diode, although its location is clearly marked near the antenna connector in the circuit board. It is just like the factory had forgotten to add those diodes to the dongles… So I had to buy a pack of 10 BAV99 diodes at a local electronics store and carefully solder one of them in its correct location. Without this diode, using an antenna placed outside, which could very possibly be charged with static electricity as a result of the friction with the wind, would have supposed a risk too high of frying the dongle. There have been people who have destroyed their unprotected dongle’s electronics by just touching the antenna connector with a finger. So this ESD protection diode is a must! Thanks to it, I’ve been able to finally stop being forced to keep the antenna inside the house when using the RTL-SDR, and improve my reception conditions with it :)
Some pictures follow (click on them to enlarge):
Well, so after finishing these dongle-related operations, how well does it work? Well, I can say that all the times I’ve used it it has performed flawlessly. Running the great SDR# software (which lacks an S-meter in my opinion, something that would be a great addition) in a HP Pavilion dv6-3182es laptop PC originally intended for flight simulation (CPU: Intel I7 720 @1.60GHz; RAM: 4.00GB; OS: W7 Home Premium 64-bit) it flows fantastically: as smooth as silk. As long as I don’t select a sample rate value higher than 2.048 MSPS, which provides me with a displayed spectrum almost 2 MHz wide (with a higher sample rate value the audio starts stuttering), the operation of the software is very stable, and there are no stutters, no cuts in the audio, nothing strange at all. As far as the reception is concerned (and setting the gain at its maximum position), this cheap RTL-SDR dongle has demonstrated to me to have a surprisingly good sensitivity (not like my IC-R5′s acute “ear”, but close…). Another point to highlight would be the really great stereo audio quality when listening to a common VHF broadcast station. Also, I had never had before the ability to have all the activity in the entire 2m amateur radio band in view at the same time, or to simultaneously monitor the activity in all the LEBL (Barcelona-El Prat airport) approach (or ground, or radar…) frequencies in the air band. I also had never had before a receiver which by default came with the capacity to demodulate SSB signals, and this is very important to me, as it means that I’m able to, for the first time, listen to SSB satellites. I’m not restricted anymore to only picking the AO-27 and SO-50 LEO FM satellites, as well as the ISS; now I can also listen to the downlink of VO-52 at 145.900 USB!!! It is awesome to think of all the things that can be made with such a small (and cheap!) device…
There are some minor drawbacks, though: in a first place, a small impedance mismatch at the antenna connector of the dongle (which has the standard impedance for all commercial radio and TV equipment of 75 ohm, vs the 50 ohm impedance used in all ham radio equipment), which in theory causes a signal loss (however, this loss is very small, so it is not a big issue; and if necessary, I could solve it through the use of an 1:1.5 unun). Secondly, there’s a small delay in the sound, about half a second or so, in comparison to a conventional receiver such as my IC-R5 (which is the time taken in the process of converting the signal to a digital format, and transferring it to the computer via the USB port; it is not a big problem if I don’t listen to the IC-R5 and the RTL-SDR at the same time on the same frequency!). And in third place, it happens that a very strong signal in one frequency easily inhibits the reception in the rest of the displayed spectrum, this is, this receiver becomes easily saturated (even if the gain is at the minimums); again not a big problem, as strong signals, at my location, appear only sometimes; and it its something I can live with.
So what’s the conclusion? Considering its high performance, its wide frequency coverage, its reduced price and the new reception capabilities this brand new SDR receiving rig has personally provided to me, and also given the small relevance, in my personal case, of the drawbacks it presents, I’ll say that it is an outstanding device, very versatile and with a lot to explore. I extremely recommend it. Get an RTL-SDR dongle. It’s an awesome receiver!!! :)