Differences

This shows you the differences between two versions of the page.

--- sdr:fm [2015/08/19 13:19] – created iggy
+++ sdr:fm [2015/09/06 11:19] (current) – mkie
@@ Line 1: / Line 1: @@
-= FM Radio stations - Reception
+= FM Radio
+== FM Radio Reception
    * Requires GNURadio
-   * Requires either an extra antenna or pressing a finger on the upper right corner where the antenna is usually soldered (then you are a human antenna ;-) )
+   * Requires either an extranal antenna(!) or pressing a finger on the upper right corner where the antenna is usually soldered (then you are a human antenna ;-) )
    * Example Script: [[https://github.com/muccc/sdr-workshop/blob/master/fm_receive/fm-example.grc|FM Radio Example]] (must be opened with GNU Radio Companion)
    * The script can be started via the arrow in the middle of the menu
@@ Line 7: / Line 9: @@
    * The Frequency can be adjusted via the FFT Plot that opens when the script is started
-==== FM Radio stations - Broadcast
+== FM Radio Broadcast
-   * Can be illegal depending on which frequency you broadcast: check the local laws
-   * Requires GNURadio
+FM Broadcast can be illegal in your country depending on which frequency you broadcast. Be sure to check the local laws before broadcasting.
-   * Requires either an extra antenna or pressing a finger on the upper right corner where the antenna is usually soldered (then you are a human antenna ;-) )
+It requires GNURadio, and either an extra antenna or broadcasting in the 2.4 Ghz band with the integrated antenna. It uses GNURadio Companion with the following flow graph:
-   * Example Script: [[http://sprunge.us/agBZ|FM Broadcast Example]] (must be opened with GNU Radio Companion)
+{{:sdr:fm_broadcast.png?direct|}}
-   * The script can be started via the arrow in the middle of the menu
-   * It uses a fifo (create it with mkfifo and change the File Source box in GNU Radio Companion accordingly). You can feed it with mp3 by executing, for example: mpg123 -r41000 -s foo.mp3 > /path/to/input_fifo. You can change the broadcast frequency by modifying the osmocom Sink configuration in GNU Radio Companion.
+The grc helper file can be downloaded here: https://ptpb.pw/gRnE.txt
+Explanation:
+The audio source has the device name **pulse** which means it will appear as a recording device for pulseaudio. It uses a sample rate of 48KHz, which is a common sample rate for an audio output. It could have been 44.1KHz. It's set in the **audio_rate** variable.
+The audio signal is passed to the **WBFM Transmit** module which gives the frequency modulated signal as the output. Its options **Audio Rate** and **Quadrature Rate** are the input sampling rate and the output sampling rate, respectively.
+It then pass through the **Rational Resampler Interpolation** module that transforms its input signal **INS** in the output signal **OUTS** defined as **OUTS=INS*(Interpolation/Decimation)**. It is used to transform our low frequency sample rate to one sample rate supported by the rad1o (it's defined in the **samp_rate** variable). The signal is then sent to the osmocom Sink (the rad1o) on the frequency specified in the variable **frequency** and piloted by a slider.
+<note tip>
+The sample rates supported by the rad1o can be listed using the hackrf_transfer command:
+## Sample rate in Hz (8/10/12.5/16/20MHz, default 10MHz).
+</note>