Software Defined Radio
Software Defined Radio (SDR) is "a radio communication system where components that have been typically implemented in hardware are instead implemented by means of software on a personal computer or embedded system." Simply put, one little chip can perform the same tasks that used to take multiple specialized devices like AM/FM radios, televisions, CBs, or ham radios.
SDR was invented in the 1970s, and since then the technology has rapidly advanced and gained popularity. Today, many SDR enthusiasts and hardware designers use low-powered devices based on the Realtek RTL2832U chip. SDR dongles can be purchased on Amazon for less than 10 USD, easily placing the technology within an affordable price range for many developers.
To prepare material for this piece, I used a Terratec Tstick+ (pictured above), on a MacBook Pro running Mac OS X 10.9.5, but virtually any generic USB dongle based on the RTL2832U chip should suffice.
Before you begin, you'll probably need to change a system setting to allow third-party and open source software to be installed on your Mac. Open Security & Privacy in System Preferences, select the General tab, and change the Allow Apps downloaded from option to "Anywhere."
Your Mac should now be able to install and run the software necessary to interface with SDR hardware. On Mac OS X, the easiest application I've found to quickly get up and running with SDR is Elias Önal's gqrx port for Mac OS X. Download the gqrx_8.dmg file and install it as you would any normal Mac application. If you prefer installing the MacPorts version, the Gqrx SDR project page contains download links for those files also.
The first time you run gqrx, you may find that you are unable to use your Mac's keyboard and trackpad. If this is the case, you'll probably need to reset your Mac's System Management Controller (SMC). Apple's provided instructions on this support page on how to do this for various types of Macs. With additional research, I discovered gqrx isn't the cause of the problem, because many users have encountered this same issue using SDR dongles with other software.
Gqrx is fairly straightforward and easy to use. The short video embedded below shows how to use it to: activate SDR hardware, change frequency and band, adjust squelch and gain, and change display properties.
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