An intro to SDRFeb 25, 2013
For the past two months I've been reading about SDR and everything related to radio telecommunications. For those that don't know what SDR is (and are too bored to click the previous link), Software Defined Radio is a system that implements hardware subsystems of a typical radio in software. People have been designing their own SDRs with FPGAs for quite some time now, but in the last year there has been a huge "revolution". It turns out that a lot of cheap USB digital TV tuners based on the Realtek RTL2832U chip can be tuned at a wide range of frequencies.
For a list of supported devices you can check this page. I've bought two devices to experiment with, one is an EzTV 645 using the FC0013 chip, while the other one is using the Rafael Micro R820T chip (bought it from ebay for about 8 euro). I mainly bought them to experiment with ADS-B and NOAA weather satellites. Due to university assignments I didn't have the time for the latter, but I've spent some mornings watching airplanes taking on and off from a nearby airport. Other interesting things to listen to are: ATC, ATIS, pager traffic, car keyfobs and anything else that is above in your chip range. As mentioned earlier, due to the lack of time, for the time being I've only experimented with ADS-B traffic.
I've done all my testing in Windows 7 using SDR# and ADSB# in conjunction with Virtual Radar Server. So far, using the stock antenna with both dongles, the one with the R820T is performing way better than the FC0013 one. There is less noise and it's better at picking signals from afar. Moreover, it has a better tuning range, although it differs from dongle to dongle and it depends more or less on your luck.
I live fairly close to an airport so I get a good signal of any plane taking on or off. The maximum range I've achieved with the R820T dongle and stock antenna (omnidirectional) is 28km. I've checked the results I get against flightradar24.com and they are spot on. One feature of ADSB# I like is the ability to share your findings with servers that accept ADS-B traffic, like contributing to flightradar24.com.
I won't go in more details at the moment, since I'm tight on time, but for those of you that are interested in getting a SDR capable dongle, do some research first. Not all dongles have what is called an esd protection diode. As its name implies, it's a diode (a passive component allowing current to flow in one direction only, like a check valve) that protects against electrostatic discharge. A lot of people have "fried" their dongles because they didn't have aid diodes. By leaving the antenna outside, the wind can create static charge on the antenna and fry the chip inside the dongle. Both of my dongles came with those diodes, but if you plan on buying one, read some comments first or if buying from ebay ask the seller for a picture of the dongle. The diodes are the ittle black things I've circled in red near the antenna connector.