NTI DiRaGen 30
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 (Transmitter 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 comprehensive 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 centre 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.
Note: The difference between the Standard and Premium exciter versions is the guaranteed DRM-SNR.
The Premium and Premium USB models will deliver >45-50dB DRM-SNR and also 20KHz DRM bandwidth.
Tuning Range: 130KHz – 30MHz (continuous) Smallest Tuning Step: 1Hz
RF Output Connector / Impedance: BNC socket / 50 Ohms Output Level: -10dBm eff. +/- 3dB typ. (thermal measurement)
Audio / IF Input Level: 0.1Vss @ 1KOhm via 3.5 mm stereo phone jack socket
DRM Output SNR: >40dB, typ. 45dB-50dB (mean value / measured via SoDiRa 072 & DREAM Transmitter)
Unwanted Sideband Suppression ( -112KHz): > 60dB
Carrier Suppression (-56KHz): >50dB (0.5 – 27MHz); typ. 65dB Harmonics Suppressions: 0-30MHz >40dB; over 30MHz >60dB Spurious Signals Suppression (0-30MHz): >35dB
Frequency Stability (15 min. warm-up period): +/- 1ppm typ. (20 °C)
Max. Baseband Bandwidth (Audio/IF): 15KHz @12KHz IF centre frequency
Power Supply / Connector: 12 – 15V DC max. 250mA / 2.1 mm DC power socket (positive inner)
Operating Temperature: 0 – 40 °C
Dimensions / Weight: 125 × 71 × 31 mm / 0.20 kg