![]() The display is showing you everything that is being received in the frequency domain, so every peak is a different signal. The FFT sink displays 4MHz of bandwidth (your sample rate is 4 million and therefore the receiver is simultaneously sampling 4 million signals every second). You are now ready to start the receiver - click on the gears icon in the menu bar and the flow-graph will start. In "WX GUI FFT Sink" set "Peak Hold" to "On", this will ensure that any signals that appear will stay displayed, even if they are transient: Note: By default the inputs and outputs are blue on these blocks, this denotes the type (blue = complex data, orange = float etc.) If the colours do not match on the connecters you are trying to connect together you will get a type-mismatch error and the arrow will go red. Select a "WX GUI FFT Sink" and connect it to the output of the receiver by clicking on the receiver output and then clicking on the "WX GUI FFT Sink" input - an arrow will link them together (if you want to unlink two blocks, click on the link and drag - it will disappear). Set "Ch0: Frequency" to be "centre_freq" and then create a new variable called "centre_freq" with a value near your target carrier frequency.Īlthough you may need to increase the gains at a later stage if the signal is too weak, initially, use the following settings: The sample rate will already be pre-populated with the "samp_rate" variable. ![]() However, if you are using an RTL-SDR, you can also just use the "RTL-SDR Source". The "Device Arguments" settings for different SDRs can be found here. All of the main receivers can be controlled using the "osmocom Source". The default is 32,000, but I would recommend at least 4,000,000 (4e6 is an easier way to write this, as you don't need to count the zeros!)ĭepending on which SDR you have will depend on which options you set here. The sample rate must be at least twice the maximum frequency (of the modulated data - not the carrier signal), but the higher the sample rate, the clearer the signal will be, which initially will help aid signal identification. Hint: When using GNU Radio Companion if you cannot find the block you are looking for in the right-hand pane, click on the magnifying glass in the menu bar and this will enable you to do a text search ![]() The Options block allows you to enter parameters such as the Title, Author, Description and also allows you to decide if the GUI elements will use the WX or QT environments (WX is the default). When you first start GNU Radio Companion, you are presented with an Options block and a Variable block. Developing an FSK receiver step-by-step Configure the GNU Radio environment
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