Monitor Internet Logo

Realistic DX-394

Radio Modifications
Realistic DX-394
DRM Module Installation

DRM Supporter Logo

Digital Radio Mondiale ( DRM ) is a digital radio system for short-wave, AM/medium-wave and long-wave. It has been endorsed by the ITU, IEC and ETSI. DRM currently covers the broadcasting bands below 30 MHz. The quality of DRM audio is excellent, and the improvement upon analogue AM is immediately noticeable. Besides providing near-FM quality audio, the DRM system has the capacity to integrate data and text. The DRM signal is designed to fit in with the existing AM broadcast band plan, based on signals of 9 kHz or 10kHz bandwidth. The DRM system uses a type of transmission called COFDM (Coded Orthogonal Frequency Division Multiplex). This means that all the data, produced from the digitally encoded audio and associated data signals, is shared out for transmission across a large number of closely spaced carriers. All of these carriers are contained within the allotted transmission channel. The DRM system is designed so that the number of carriers can be varied, depending on factors such as the allotted channel bandwidth and degree of robustness required. The DRM system can use three different types of audio coding, depending on broadcasters’ preferences. MPEG4 AAC audio coding, augmented by SBR bandwidth extension, is used as a general-purpose audio coder and provides the highest quality. MPEG4 CELP speech coding is used for high quality speech coding where there is no musical content. HVXC speech coding can be used to provide a very low bit-rate speech coder. The robustness of the DRM signal can be chosen to match different propagation conditions.

All you need to receive DRM transmissions is a PC with a sound card and a modified analog short-wave (MW, LW) receiver. The DX-394 has a 455kHz IF and with a downmixer it produces the 12kHz DRM signal that is fed to the microphone input on your computers sound card. Finally, you will need some software to decode the DRM signal and the good news is ... it's FREE!!

Download qt-mt230nc.dll

Monitor Internet DRM Board features:
  • Power supply 9 to 20V dc
  • Current consumption < 15mA
  • Downmixer from 455KHz to 12KHz
  • Input Impedance 470K
  • DRM 12kHz output signal voltage: 25 to 50mV r.m.s
  • Sat- Service Schneider DRM Module 20mm x 20mm
  • Monitor Internet DRM Board 60mm x 22mm

Modified Hi-Z Antenna Socket

DRM 12kHz Data Output
Modified Hi-Z Antenna Socket

Monitor Internet DRM Board

455kHz IF Amplifier, Ceramic Filter and DRM Module

DRM Circuit Diagram

DRM 455kHz to 12kHz Converter

Parts List
Component Type Value Quantity
Resistor 100R 0.6W 2
Resistor 220R 0.6W 1
Resistor 1k 0.6W 2
Resistor 1.8k 0.6W 1
Resistor 4.7k 0.6W 1
Resistor 10k 0.6W 1
Resistor 470k 0.6W 1
Ceramic Capacitor 47pF (47) 50V 1
Ceramic Capacitor 0.01uF (103) 50V 1
Ceramic Capacitor 0.1uF (104) 50V 3
Ceramic Filter CFW 455 F (10kHz BW) 1
FET Transistor BF245A 1
PNP Transistor 2N3906 1
DRM Module Sat- Service Schneider 1
Circuit Board Plain Matrix Board 1
The resistors are Metal Film 1% 0.6W. Dimensions: 6.5mm x 2.5mm dia.
However, you can use 2% or 5% resistors at 0.5W or 0.25W.

The small blue capacitors are resin-dipped high quality multilayer plate ceramic.

Mounting The DRM Board
The DRM module has two mounting holes that are used to retain the unit inside the DX-394.
M2.5  Fixing Bolts

M2.5 Fixing Bolts
Circuit Board Mounting

Circuit Board Mounting
M2.5 Hardware

M2.5 Hardware

DRM Board Wiring
DRM board Connections

455KHz / 12KHz and Power Connections

+V Power to DRM Board
+V Power to DRM Board

+V Power to DRM Board

+V Power to DRM Board

455KHz IF Pickup Point
455kHz IF Output TP1

455kHz IF Output TP1
Modified 455kHz IF Output

Modified 455kHz IF Output
455kHz IF Output
Modified 455kHz IF Output
If you have not yet done the 455kHz IF modifications the IF pickup point is at TP1 shown in the above Photo and Circuit Diagram.
If you have already done the 455kHz IF modifications a more convenient pickup point is shown in the above Photo and Circuit Diagram.

DRM 12kHz Data Output

Modified Hi-Z Antenna Socket

DRM Module Input Level Adjustment

DRM Input Level

DRM Input Level Control
Set the Input Level to the halfway position.

DRM Module and Software Operation