Software Defined Radio (SDR) is a radio communication system that has been taken from a special hardware platform and placed onto the computer platform.
A basic SDR can consist of a computer with a sound card, which is fed by an RF (Radio Frequency) front end. All of the signal processing is done by the computer / software. The software can define the "radio." By changing the software you can receive / transmit on the amateur radio bands, AM, FM, and TV.
Links:I have finally started using gnuradio. I have a vehicle that does not have NOAA as a part of it's radio. Researching gnuradio, I was able to put together a flowchart that I was able to tune in my local NOAA station. I set up the GUI ease of use while mobile, including the ability to change frequencies while moving city to city.
Using this SDR on my desktop is fine. But using it on the Raspberry Pi 3, not so much. As of now, I can't say what the issue is, the Pi, the USB 2.0 port that the dongle is plugged into, the built in audio jack, or a combination of all three. From my research, it seems that there should be no issue using gnuradio on a RPi 3, except maybe when it comes to the audio jack. Can it be the generation RTL-SDR dongle? Probably not. As a test, I installed gqrx on the RPi and everything works fine. I have spent time tweaking the blocks in the flowchart, to no avail.
So, having the NOAA radio working would be great. This is what started me researching gnuradio in the first place. Once I had it working on my desktop I then utilized the same flowchart for the 2-meter amateur band and CB radio. These two SDRs will not be needed eventually because I hope to have my CB radio and dual-band transceiver installed at some point. So in the meantime, they are part of my app. I could use gqrx for tuning in NOAA broadcasts only, but I am not sure how well that will work while driving.
I have to mention how suprised I was at how the RTL-SDR dongle operates over such a wide range of frequencies using the 4" antenna that came with it. When I first used it with gqrx on my desktop tuning in the 2-meter band, the reception wasn't so good. I almost ordered a cable to allow connection of my dualband antenna. But with moving everything around to different areas of my apartment, I found the right spot. I also setup xastir (on my desktop) for ADS-B. There is no problem receiving at this higher frequency. I even tried using the Kalibrate utility to see if I can get a frequency offset that I could use with gnuradio. I will definitely need to be outdoors for this to work. At best, indoors is iffy. I can sometimes pick up a tower and then another day not. Overall I am happy with the performance of this little device!