NTI DiRaGen 30
Shortwave DRM Exciter
Generating Shortwave DRM – Radio Signals. The importance of the digital shortwave radio standard DRM (Digital Radio Mondiale) continues to grow rapidly. With the DiRaGen 30 we introduce an exciter which converts a PC-generated DRM signal to the shortwave range.
What is needed?
1. DRM-Transmitter Software
Actually the following transmitter software is available for generating a DRM signal via PC & sound card:
– DREAM (Transmitte Mode)
– SPARK DRM Transmitter
DREAM the pioneer for DRM open source software contains an additional DRM-transmitter module which allows transmission of text & image files.
SPARK is an actual real-time software modulator developed by Michael Feilen. The software is very comprehensive and a free (non commercial) version is available on request from the author.
This software offers numerous possibilities and supports all code rates, bandwidths and robustness modes. A comprehesive documentation is also available.
Besides pure audio transmission basing e.g. on a WAVE file source additional transmission of text & image files is also possible.
There is also a commercial version with additional features available.
A PC or notebook equipped with a standard (AC 97) sound card allows the generation of a DRM signal.
The low-frequency DRM Baseband signal is available at the line output of the sound card as OFDM (Orthogonal Frequency Division Multiplex ) signal.
The standard center frequency of the OFDM signal is 12KHz.
3. DiRaGen 30
The sound card OFDM signal is connected to the audio/IF input and converted in the shortwave range.
Any output frequency can be selected within 130KHz to 30MHz directly via the integrated keyboard. The last selected frequency is stored automatically and permanently visible at the front display.
Generating a DRM radio signal according to standard:
Output signal of the NTI DiRaGen 30 generated in combination with DREAM transmitter and received via SoDiRa & direct conversion receiver on 10MHz test frequency.
Highest linearity and easy to operate
In order to achieve the highest possible signal-to-noise ratio (SNR) the conversion must be absolutely linear. Overloading or compression degrades the SNR severely.
The DiRaGen has an easy-to-read integrated overload control (red LED) at the rear panel. Adjust the PC volume (audio level) control settings until the LED starts just to flicker. This is the optimum level to reach the highest possible SNR.
Due to a high performance design with triple frequency conversion in combination with efficient filtering very good unwanted sideband rejection and carrier suppression values are achieved.
All internal frequencies are derived from a stable crystal clock generator (master clock) to prevent odd frequency drifting effects.
A Direct Digital Synthesizer (DDS) acts as VCO combining good phase-noise and short time stability. We use this reliable principle already for our PC-controlled shortwave receivers.
Please note. In case of further amplification of the RF output signal additional selective filters must be inserted.
Furthermore the legal regulations shall be observed.
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