I've no experience whatsoever in radio, only in software. Where should I start? What should I buy to begin with? Any general technical advice?
I've used the FunCube Pro+ dongle for amateur radio stuff. It's very narrow-band (it's based on a sound card as the ADC) but it does cover most of the important amateur radio bands (HF) which most SDRs you find on the Internet do not without additional hardware. It also has special filters around the 2m and 70cm amateur bands, the filters on 2m are especially nice because strong FM radio stations tend to desense the cheap receivers here (RTL-SDR, HackRF IIRC).
At work we use the USRP (B200) for WiFi-related testing, requiring the ability to receive and transmit above 5GHz over 80MHz of bandwidth. The RTL-SDR is not going to do that. (Actually the B200 doesn't quite cover 80MHz, but it's good enough.)
For actual amateur radio work I use an Elecraft KX3 with the 2m module. You can't beat the sensitivity of an entire system engineered to be sensitive. With off-the-shelf SDRs (the KX3 is SDR-based) there are going to be a lot of issues to debug to get the full system performing well. Fortunately, most of the hard parts have to do with transmitting at higher powers, so you might not care if you just want to listen.
A few friends have tried either the BladeRF or HackRF (I don't remember which) and find that it uses an IF near the FM broadcast band, and hence they couldn't get it to work reliably in Manhattan where they live because the IF stages are desensed by the super-strong FM stations nearby. Of course, debugging this is going to require already-working radios and test equipment (oscilloscope/spectrum analyzer). So these cheaper SDRs are not off-the-shelf instantly-working solutions. They're more of another thing that's helpful to have in your lab. You probably don't want to tie up your $10,000 FTDX9000MP to be a WSPR beacon, so you find a good-enough SDR instead and use that.
Finally, the good news is that most of the people writing software for the radio experimentation community know radio and not software, so there is plenty of room for improvement if you care to work on the software.
I've had a ham radio license for a little over 21 years so I've always been interested in radio but the whole SDR thing is new to me. I still really haven't done a whole lot with it but it's fun to play with.
The neatest thing I did was set it up on the balcony of our 23rd floor condo on Panama City Beach (facing the Gulf of Mexico) and used dump1090 [1] to plot aircraft locations (using ADS-B) on a map. I was able to "see" planes a few hundred miles away (thanks to the height and facing out over the water) but was also able to see them at pretty much ground level.
I have access to a bunch of buildings (mostly on top of big hills) across the southern portion of Indiana thanks to my job and have been thinking about building a bunch of "ADS-B receivers" (using Raspberry Pi's or similar) and putting them out in these buildings so that I can cover a wide area. (I really only probably need about three as long as I put them in the right locations, geographically speaking.)
Edit: I do need to find a good external/outside antenna designed for 1090 MHz, if anyone has any firsthand recommendations.
In addition, at one of these locations there's a communications tower used by a pager company to transmit pages so I've thought about building a POCSAG receiver with one of these devices as well.
Unrelated to SDR, but I'm also planning on putting together a bunch of stratum 0 NTP servers (using GPS) and deploying them at these same locations as well. They will primarily be for my own use at work (ISP) but I expect to make publicly available a few stratum 1 servers as well.
[1] - https://en.wikipedia.org/wiki/Automatic_dependent_surveillan...
You can make an external ariel with a bunch of 11cm coax elements coupled together and placed inside a piece of 1/2 plastic pipe.
But it took me a while to figure out I had to kalibrate it, using the GSM network.
http://www.rtl-sdr.com/how-to-calibrate-rtl-sdr-using-kalibr...
The badge [0] (called rad1o) is a hackrf-compatible SDR for frequencys between 50 and 4000 mhz.
Maybe somebody at a local hackerspace went and is willing to trade you his?
When I was at CCC camp I made node.js bindings for the hackrf, so it's pretty easy to work with: https://github.com/mappum/node-hackrf, https://github.com/mappum/hackrf-stream
They've also got some good tutorials on using GNU Radio Companion.
I'd recommend an RTLSDR, USRP, or HackRF. All good, all different price range, and all have a good community and support around them. If you're interested in a particular band, you may want to get an antenna for that band as well. Ettus Research sells some antennas, or you can buy one from an amateur radio store, or build one for very cheap from the dozens of plans out there by ham radio operators.
I started with listening to NOAA weather stations[1], and now I'm tracking aircraft with PiAware[2]
[1]: https://jaredharley.com/2015/08/25/software-defined-radio-sd...
[2]: https://jaredharley.com/2015/08/31/tracking-aircraft-with-pi...
I have one of the USB DTV receivers and it was fun for exposure but hard to do really interesting stuff with. I got the HackRF One and it has been a lot of fun, I added the Ham-it-Up so that I could easily play around in the HF and AM bands. For my bluetooth work I ended up getting an UberTooth even though the HackRF One should be able to do what I need, the Ubertooth was more compact and simpler to set up and take down.
In my case I'm interested in mesh network wireless systems for robotics and room / house localization for those robots. I also have one of the newer Crazie Fly quad copters and want to get to the point where I can manage it using software.
The important thing is to pick a unit that can operate in the frequencies you are interested in (the HackRF One goes 1Mhz to 6Ghz so its pretty wide open) and be ready to revisit a lot of math you might have considered less than useful back in school (complex numbers).
Really though maximum value per $ is probably though starting with one of the USB DTV receivers. If you find you hate it, or its too steep a learning curve, then you won't be out all that much.
The RTLSDRs are definitely the best value (get one with a metal box around it). Also look for the HackRF Blue.
Finally, think hard about what you want to do. You mention decoding TV signals but the RTLSDRs can't do that (in America at least) since they can only do about 3 MHz of instantaneous bandwidth and TV signals are 6 MHz wide. You could try using 2 or 3 RTLSDRs for that but then you'd have put them all on the same clock, which can be difficult.
If you can spend around $1500 I'd go for a B200 with a GPSDO. GPSDOs let you accurately timestamp signals and time evens (i.e. start transmitting at some specific time). In my eyes the 210 isn't worth the bigger FPGA and dual transceivers. The isolation between the transceivers probably isn't great (but I could be wrong) and a bigger FPGA isn't worth anything to me.
If you like the RTL-SDR after playing with it a while and have a bit of money ($300) I'd strongly recommend the HackRF One. I only started with SDR a few weeks ago and the RTL-SDR was great (especially for the price) but the HackRF One is a whole other level. The amount of bandwidth you can get out of it is amazing.
If you're hoping to handle weather satellites and such, you'll need to build your own antennas. They can be kinda big and you'll need line of sight to the sky most of the time so it'll work best if you have a large open area you can frequently visit. If you own a house your back yard might be good. If you're in an apartment building the roof or parking lot is probably best.
Something else that's fun to play with is ADS-B. It allows you to pick up air traffic position/altitude/speed/heading broadcasts.
I purchased a "RTL-SDR Blog R820T2 RTL2832U" a month ago. It has an upgraded oscillator (less setup hassle) and comes with a usable antenna. In the Bay Area I've been able to listen to FM radio, NOAA weather, SJC Airport tower, Police - both NFM and digital, and ADS-B.
I'm quite happy with the purchase, and excited about the possibilities of what I can do next.
I'm also curious ... are these cheap USB dongles just receivers? Or do they have ones that can transmit as well (i.e. transceivers).
If anyone with experience on SDR transceivers has some input here, that would be great!
i also buy commercial grade hardware., as rtl-sdrs can be a little dodgy due to low tolerace components, so weak signals are hard to digout of a sound floor with cheapo dongles.