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
- 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 seleted
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 DiRaGen
30 generated in combination with DREAM ransmitter and received via SoDiRa &
direct conversion receiver on 10MHz test frequency
(Robustness Mode B, MSC Protection Level
0, MSC Interleaver Mode 2s, Bandwidth 9KHz, IF 12KHz)
Highest linearity and easy
In order to achieve the highest
possible signal-to-noise ratio (SNR) the conversion must be absolutely linear.
Overloading or compression degrades the SNR severly.
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
Furthermore the legal regulations
shall be observed.
of DRM receivers, laboratories & testing facilities
a standard DRM signal for demonstration purposes
test transmissions & DRM transmitter
Tuning Range: 130KHz - 30MHz
Smallest Tuning Step: 1Hz
RF Output Connector / Impedance: BNC socket / 50Ohms
Output Level: -10dBm eff. +/- 3dB typ. (thermal measurement)
Audio / IF Input Level: 0.1Vss @ 1KOhm via 3.5mm stereo phone jack socket
DRM Output SNR: MER>40dB,
typ. 45dB (mean value / measured via SoDiRa 072 & DREAM Transmitter)
Unwanted Sideband Suppression ( -112KHz): > 60dB
Carrier Suppression (-56KHz): >50dB; typ. 65dB (0.5 - 27MHz)
Harmonics Suppressions: 0-30MHz >40dB; over 30MHz >60dB
Spurious Signals Suppression (0-30MHz): >35dB
Frequency Stability (15min. warm-up
period): +/- 1ppm typ. (20°C)
Max. Baseband Bandwidth (Audio/IF): 15KHz @12KHz IF center frequency
Power Supply / Connector: 12 - 15V DC max. 250mA / 2.1mm DC power socket (positive
Operating Temperature: 0 - 40°C
Dimensions / Weight: 125 x 71 x 31mm / 0.20kg
What`s included ?
Please note: Plug-Power Supply,
application software and connecting cables are not included !
Selected DiRaGen 30 with
DRM-SNR >45dB guaranteed
ask for availability !
As a DRM-Brasil founder member
and as a DRM researcher I can say that NTi
plays a very important role in pushing DRM forward providing affordable
equipment for demonstration and trials.
The DiRaGen 30 together with the PostAmp provides an incredible
equipment for DRM demos.
Not to forget the great DRM software
modulator - SPARK, that works
perfectly with the NTi chain.
I do recommend to anyone who is interested in trying DRM here
in Brazil and worldwide,
talk to Rudolf of NTi.
Rafael Diniz / Brazil