DRM sigla of it Radio Digital Mondiale, DRM (Radio Digital Mundial) is a digital radio standard that is designed for broadcasters, with the support and participation of transmitters and receivers manufacturers and other experts in the field. It was specifically designed as a high quality digital replacement for current analogue broadcasting in AM and FM bands.
Now SDR sigla of it Software Defined Radio (Radio defined by Software), designed for communities, government, commercial amateur radio and shortwave listener, the software provides a powerful interface for decoding, demodulation and filtering radio signals in digital form.
In this article we show a homemade converter, which is a very sensitive interface that allows you to receive DRM radios and use SDR with a common short-wave receiver and a PC or notebook.
DRM SDR Converter
The circuit is very simple and can be adapted to any commercial radio that has the FI (intermediate frequency) of 455kHz. The circuit is very stable, low noise level, sensitive, low power consumption (13 mA) SA602 and is based on integrated circuit is a mixer / RF oscillator, substitutes with NE602, NE612, SA612 and other substitutes may be used.
List of components of the DRM converter / SDR
= IC1 NE602
IC2 78L06 =
Q1 = BC109, BC107
C1, C4 = 2.2uF / 25in
C2, C3 = 100nF
C5 = 470pF
C6 = 100nF (polyester)
C7 = 68nF (polyester)
C8 = 100nF
C9 = 1nF
C10 = 820pF
C11 = 100pF trimmer
C12 = 220pF
C13 = 1N5 (field)
C14 = 220nF (polyester)
C15 = 2N2 (mylar, field)
C16 = 220nF (field)
C17 = 120pF
Cf = 465B (ZTB465 kHz, or 470kHz) ceramic filter
R1 * = 10k
R2 = 1K8
R3 = 10k
R4 = 1k
R5 = 100k
R6 = 2K2
P * = 2K5
Setting the DRM / SDR Converter
The most critical component is the ceramic resonator crystal Cf which is a simple ceramic filter 3 pins or 2 the frequency of pins 465 kHz or 470 kHz. This crystal filter can be found in older wireless telephones or radios transistor AM / FM, etc.
If the result of the mixture does not reach the 12 kHz, which is the frequency necessary to obtain the seamless connection between the radio and the PC, you will need to add a capacitor in series with the the ceramic crystal Cf, this capacitor must be disk with a value between 100pF and 300pF, you can also use a trimmer for easy adjustment (as seen no scheme) . R3 adjusts a better signal / noise, therefore, sets the maximum converter output.
455 kHz = Radio FI
467 kHz = DRM converter SDR Oscillator
467-455 = 12kHz
The result in the output is 12kHz
The DC converter voltage can be tapped from the radio itself, if it is 6 Volts you can remove the regulator integrated circuit IC2, but any tension between 8 até 18 volts can power the converter circuitry since it uses a 78L06 regulator.
SDR Converter for common shortwave radios
The great advantage of this converter circuit is the use of software defined radio or SDR, this system has a large number of applications, with this can turn a simple radio shortwave AM on a powerful radio listening, as it demodulates SSB , AM, FM, and other modes of transmission, beyond the DSP.
DSP is the acronym of Digital Signal Processing, you can handle signals after being converted from analog into digital form. Normal analog filtering operations, mixture, and signal detection, all have their parallel in the world of DSP. The cost of complex digital processing is very low, DSP is often EM The best way to build high performance communications systems and low cost.
If everything is right, connect the circuit output additional or microphone input of your computer. Install software DRM or SDR to begin testing, Try to find a radio station, (see list of radio stations broadcasting on DRM) in the case of DRM, just to find the audio it should start playing on computer speakers. In the case of SDR is simpler, because it decodes any radio transmission, simply you tune any signal and start listening using the appropriate type of demodulation for audio listening.[Source]