Software Defined Radio
DiRaGen 30 USB
SPARK Modulator
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SPARK Modulator - An universal transmitter software to generate broadcast signals
The following review introduces the SPARK software in combination with the DiRaGen 30 USB including all important screenshots. The DiRaGen is recognized automatically by SPARK as external device.
Please note: To keep this review simple all irrelevant settings are ignored.
For more informations about SPARK please use this link: www.drm-sender.de
The software is well structured and is compatible with Windows 7, Windows Vista, Windows XP and Windows 2000.
Before generating an output signal all the required unique settings have to be set. After this procedure these settings are automatically loaded when starting the program again.
Additionally a brief explanation of each option is given as the mouse passes over it.
It is also possible to store a time-controlled automatic switching configuration, e.g from AM to DRM.
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Configuring transmission content & data - Content Manager
FAAC or AAC+
FAAC: Monaural AAC audio stream without spectral bandwidth replication (SBR) and without parametric stereo (PS).
Optional AAC+: Licensed DRM Dolby AAC+ audio stream supporting SBR and PS.
Slideshow
The slideshow substream allows the cyclic transmission of pictures in various formats (e.g. JPEG, GIF, BMP, etc.) and is carried by a packet data stream.
Website
The files that are required to render a website on the receiver must be placed in a certain directory. The contents of this directory can then be transmitted using the MOT website substream which is carried by a packet data stream. The user must define an entry page which indicates the first page the receiver is advised to display (e.g. an index page of a website).
PRBS
The pseudo random binary sequence (PRBS) can be transmitted in synchronous or asynchronous mode.
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Example: Generating a FAAC data stream
Audio Input Device: Selecting an audio source (MP3-Playlist, soundcard input or WAVE file).
Stream Datarate
Stream Bandwidth: The Stream bandwidth input field enables to adjust the number of bytes reserved for this stream. Maximum usable bandwidth depends on selected MSC-, channel- and transmission parameters.
High Protected: The High protected input field lets the user choose the percentage of high protected bytes with respect to the bandwidth of the stream. It is recommended to choose values between 0 and 50 percent for the higher protected part.
Text Messages
DRM allows for text message transmission in parallel to an audio broadcast. The maximum length of a text message (headline and body) is 128 bytes, whereas the number of usable characters varies with respect to the characters used due to the unicode transformation format (UTF-8) coding.
In the text message submenu a list of text messages can be defined which are transmitted in the order in which they occur in the list. A text message is divided into headline (max. 32 characters) and body.
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DRM and AM settingsThe transmitter settings tab contains the configuration parameters for the modulation and the output devices.
DRM: All modes from 4.5 to 20KHz occupied OFDM bandwidth according to DRM 30 are supported.
AM: Possible settings are the occupied bandwidth (max. 2x audio bandwidth), modulation index (max. 1.00 = 100%), AM mode (Double Sideband or Single Sideband), switchable carrier suppression and additional service information AMSS (Amplitude Modulation Signalling System).
Output settings
Modulation
Transmission Mode: DRM via OFDM, AM and AMSS
The DiRaGen 30 is connected to the line output of the soundcard.
Intermediate Frequency ( IF): The center frequency of the generated basband signal. For applications up to 15KHz bandwidth the standard value is 12000Hz = 12KHz.
Output Frequency: The output frequency of the DiRaGen device, e.g. 10000KHz = 10MHz.
OFDM Postprocessing
These selectable parameters detemine directly the shape and spectral purity (Spectrum Shaping) of the output signal.
FIR Filtering: Spark uses extreme sharp FIR filters with a order > 3000 for superior spectral purity, always activate >>> ON.
Sideband Suppression: The sideband suppression defines the attenuation of the output signal from the beginning to the end of the transition region. Recommendation for DRM: 50dB
FIR Transition Bandwidth: The transition bandwidth parameter modies the steepness of the filter transition region and is given in Hz. A small transition bandwidth requires a higher filter order but gives a steeper sideband rolloff.
Recommendation for DRM: 500HzEnable Output AGC (Automatic Gain Control): The level of the generated baseband signal will be regulated automatically >>> ON
PAPR
Peak-to-Average Power Ratio: Soft-clipping und peak-windowing are selectable to reduce the crest factor for DRM.
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Going on air ...
After the application configuration has been finished, the transmission can be started by pressing the start button:
SPARK transfers the frequency information to the DiRaGen 30USB.
First the yellow CONNECTED-LED does light up followed by the red ON AIR-LED.
Simultaniously SPARK starts a new window with a modulation monitor showing the spectrum of the generated basband OFDM output signal together with the selected parameters.
DRM signal
AM signal
Watchdog
An integrated watchdog function of SPARK checks continously the connection to the DiRaGen device. In case of a detected interruption or distortion (e.g. power loss) the DiRaGen is automatically reinitalized.
In the following a simulated short-time loss of supply voltage shown on a waterfall diagram:
Immeditely after the interruption the output signal is switched off for safety reasons and to prevent RFI. About six seconds after the interruption SPARK has recognized the distortion and reinitalizes the unit completly. The interrupted transmission is continued with the selected parameters.
