Hello, I am surprised I have not seen these discussed here. Certain RTL2832U chipset based DVB-T dongles sold in much of the world for almost nothing, basically around $10-15 - for watching DVB-T digital TV, were discovered to work as software defined radios in a sort of test mode around two and a half or three years ago.
(a common nickname is "RTLSDR" or "rtl-sdr" )
See
https://sdr.osmocom.org/trac/wiki/rtl-sdr - that is the main site for the rtlsdr software where you can download the drivers for linux and windows directly, on Mac OSX you can compile the Unix drivers from source using the same instructions as for Linux or install librtlsdr, gr-osmosdr, gnuradio and gqrx from macports.. gqrx (
http://gqrx.dk ) also has a drag and drop installer that installs the gnuradio libraries on OSX.. good for a quick start, macports is better for seasoned users. two good Windows programs you can use with them are at
http://hdsdr.de and
http://sdrsharp.comFor support, there is a forum at
https://www.reddit.com/r/RTLSDR its a good starting point for beginners..
they are a real phenomenon..
Their sudden and quite unexpected discovery has basically kicked off a lot of interest in SDR around the world, because they really are such an extraordinary value.
They make a very decent radio for receiving almost anything that will fit in up to around a 2-3 MHz slice of spectrum from roughly 25-1750 Mhz. (typically around 2.6 Mhz without any dropped samples, and up to 3.2 MHz on a good day - if you don't mind occasional errors and sudden quits- that ability is great for doing screenshots on a lightly loaded machine.)
Thats really an engineering marvel, given the size (smaller than your finger) and cost (less than the cost of a good movie for most people, including shipping)
What else can be done.. really, a hell of a lot.. you could use them for teaching DSP, a number of schools do exactly that.. FM radio on them works great, you can also receive stuff as diverse as weather satellites, public safety transmissions, GPS (with a bias tee and an amplified GPS antenna) ADSB ) aircraft tracking signals) AIS, the list just goes on and on.. and even shortwave (with an HF upconverter or direct sampling).. radio astronomy, and so on.. You can receive all sorts of digital modes.. as you can see from the long list of compatible applications on the osmocom site, also Gnuradio - basically a tool kit for writing radio applications which run using a combination of C and python code.. in a notebook style format..has several dozen pre-made apps.. (
http://Gnuradio.org ) is a development environment "gnuradio companion" or GRC with which you basically connect signal sources and functions and sinks with signal path lines, just connect them with the lines.. and doing this you can literally prototype almost any kind of radio system with drag and drop on a screen, then you compile them and zap, after a bit of tweaking, they work! Its serious radio fun, a very powerful tool and you also learn a lot very fast. they are also so cheap you can give your boisterous kids, (co-workers, etc.) one and not worry if it will get broken.. (although i would recommend getting several both for backup as one never knows how much longer they will be around)
They make good IF stages for dedicated task specific radios, and they are so small they can be mounted right at the antenna feed point and fed using a USB extension instead of coax. No other radio i know of can do that.
Some important things to remember..
otherwise you might never get it working as it should and get frustrated and give up which would be a tragedy because they almost always work great once you learn their quirks.. 1.) the supplied antenna is worthless, and the "coax" connecting it isnt even coax, its microphone wire..
Don't use it. Buy an adapter when you buy the dongle (or better yet buy several) so you can use yours with BNC, SMA, F, etc..
2.) Use a USB extension, a good one - and a bunch of snap on ferrites - 2 minimum, but preferably more. Also put some on any nearby RFI-producing devices, like monitors, etc. Use the longest USB extension you can if you need to get the device away from your computer (which generates a lot of RFI crap).. which more likely than not will not show up on your screen it will simply desensitize your receiver and you will think its broken.. thats a quirk they have.
When you add ferrites the signal will magically come out of the noise..
3.) Use a good antenna, it can be home made.. for example, here is a good very simple ten minute antenna you can make out of two dollar store pizza plates and some coax. You can use RG-6, CATV coax..
http://www.wa5vjb.com/references/PlanarDiskAntennas.pdf There are roughly 6000 videos on youtube about various things one can do with them. You can do hundreds of different things with them. feel free to PM me, I know a fair amount about them and have helped get a lot of people started with them.
They would make a great subject for a show- or even several shows, as they literally are one of the most fun and flexible and cheap electronics devices out there, they must win some kind of prize for incredibly high value for money, as they can in many cases do things that otherwise would require very expensive radios to do. They have sort of kicked off a huge amount of interest in software defined radio around the world, including in Australia. For example, as you can see in the image below, ( and also at SM5BSZ.com ) they can be used as a quite functional very low cost spectrum analyzer.. the ADC chip in them could also be used for other kinds of sampling, I bet. To make lots of super cheap test equipment that perform surprisingly well considering its very low cost and extremely tiny size.
Anyway, the search string rtl2832+r820t on ebay will bring up a bunch of them. The one in the image below is a good choice, as it has a slightly better crystal than most of them, (more accurate and less drift) as well as a robust, durable PAL style antenna connector and what has proven in my experience to be a very sensitive receiver.
Make sure whatever you buy has an RTL2832 and a R820T
I've attached an image of a approximately 3 Mhz slice of HF (shortwave) spectrum, captured using a long wire antenna and an up-converter. It samples at 8 bits so its not as good in some respects as some much more expensive SDRs but for the money it really is pretty amazing. Each one of the lines in the attached PNG picture is a signal. It can record all of this spectrum to disk at the same time if that is what you want.. (that eats up a lot of disk space very quickly) They also make excellent FM radios. You can see 2.5-3 MHz of spectrum as you listen.. so you learn a lot about radio by tuning around..
Anyway, highly recommended.