User:Gyromax Balance

Immediate frequency downconverter (V0.2)

Overview

File:Http://www.sat-schneider.de www.sat-schneider.de/deutsch/LCMIX.jpg

A universal DRM- miniature mixer unit (surface mount)from 455 KHz or 10.7 MHz to 12 KHz (input of a PC-soundcard), designed for modification of existing AM-broadcast receivers to be able of DRM-receiving by use of the softwaredecoder from Fraunhofer Institut für Integrierte Schaltungen or other softwaredecoders.

An immediate frequency downcoverter is a device to convert an immediate frequency (IF) wave at higher frequency, or 455MHz usually used in superheterodyne radio receiver, to a lower one carrying identical signal, 12KHz usually, applicable to be processed by personal computer (PC) input through sound card substentively which a role of anolog-digital (A/D) and digital-anolog (D/A) card at sampling rate of 192kHz, as PC becomes a powerful but cheap computing resources availabe world-wide due to fast development of information technology (IT) revolution since 1990s.

Virtually overwhelming majority of modern radio and television receivers use the superheterodyne principle. IF downconverter makes further use of such a huge number of radio receiver and over 100 years aged radio industry revitalized from rapidly dying fate due to rapid update to digital system. Generally, the IF downcoverter, as cheap as anything if configurated fundamentally, sets overwhelming radio listeners, even entire audience, free from purchasing too expansive digital radio receiver. As conventional radio boardcasting programs cover a band interval between 100KHz or lower up to 30MHz, technically, modification of such radio receiving sets by mounting an IF downconverter builds a bridge between aged radio receiving sets inhabited by this audience and ever-updated IT industry permeating variety of sectors as much as possible.

Thus, some people regard IF downconverter as an excessive device disappearing sooner or later, others argue that it is a long-term design because opening a fresh field of radio services lower than 30MHz including audio, text, still image, even video (MPEG4) programs.

How it works

In telecommunications, a mixer is a nonlinear or time-varying circuit or device that accepts as its input two different frequencies and presents at its output a mixture of signals at several frequencies:

1. the sum of the frequencies of the input signals
2. the difference between the frequencies of the input signals
3. both original input frequencies — these are often considered parasitic and are filtered out in subsequent filter stages.
   • a balanced mixer passes only a small leakage of the original signal to the output, often implemented as a double balanced mixer which has high isolation of both inputs.
4. unwanted intermodulation products from the inputs.

Gilbert cell

In electronics, the Gilbert cell is an electronic multiplying mixer first described by Barrie Gilbert in 1968. The output current of the circuit is an accurate multiplication of the (differential) base currents of both inputs.

Basic circuit of a Gilbert cell

The Gilbert cell consists of two differential amplifier stages formed by emitter-coupled transistor pairs (Q1/Q4, Q3/Q5) whose outputs are connected (currents summed) with opposite phases. The emitter junctions of these amplifier stages are fed by the collectors of a third differential pair (Q2/Q6). The output currents of Q2/Q6 become emitter currents for the differential amplifiers, therefore the output currents of these stages are linearly dependent on these emitter currents and the respective input voltages. Combining the two difference stages' output currents yields four-quadrant operation.

A functionally equivalent circuit can be constructed using field-effect transistors (JFET, MOSFET) or vacuum tubes.

History

Time line

• 1996.9 Digital Radio Mondiale (DRM) emergs from an informal meeting in Paris, France, between some large international broadcasters and broadcasting equipment manufacturers, including Radio France Internationale, TéléDiffusion de France, Deutsche Welle, Voice of America, and Thomcast. During this meeting, a consensus emerged that unless something was done, the days of national and internation broadcasting in the AM bands below 30MHz were limited.
• 1998 DRM Consortium is formed when a small group of pioneering broadcaster and manufacturers joined forces to create a universal, digital system, DRM, for the AM broadcasting bands in HF, including short waves, medium waves and long waves. By then DRM is an international consortium of over 70 broadcasters, manufacturers, network operators, research institutions, broadcasting unions and regualtory bodies, with members represent over 25 nations as varied as Australia, China, Ecuador, Finland, France, Germany, India, Japan, Luxembourg, Nigeria, Spain Tunisia, The USA, or the United Kingdom.
• 2001.9 DRM Technical Specification of the European Telecommunications Standards Institute (ETSI): ETSI TS 101 980 V1.1.1 (2001-9)
• 2002 DRM specification: PAS 62272-1, ITU Recommendation BS 1514-1 for broadcasting bands spanning 150k-30MHz
• 2003.1 DRM standard: International Electrotechnical Committee (IEC) adopts IEC 62272-1
• 2003.12 Second generation of DRM, supports transmissions in mono, dual mono or stereo
• 2005 1st software defined transceiver sold by FlexRadio Systems, an US manufacturer compatible with amateur modes (SSB, CW, AM, FM, RTTY, PSK) and DRM: SDR-1000, working on both HF and VHF bands with an output of 100W in HF and 50W in VHF. It look like to a passive peripheral, a black box standing on your desk totally controlled by a software named PowerSDR, for now only accessible to computers running Windows XP Home Edition with Service pack 2. Its by-then price ranges between $1375 to $2500.

External links

1 Introduction

2 Features and User Guide

3 Hardware

4 Source Code

5 Installation

6 Auxiliaries

7 Design

8 Forums

9 Disclaimers

1. Introduction

1.1 What is "immediate frequency"?

In communications and electronic engineering, an intermediate frequency (IF) is a frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception of signal. The IF is created by mixing the carrier signal with a local oscillator signal in a process called heterodyning, resulting in a signal at the difference or beat frequency. IFs are deployed in superheterodyne radio receivers, in which an incoming signal is shifted to an IF for amplification before final detection is done. There may be several such stages of intermediate frequency in a superheterodyne, which is called double (or triple) conversion.

Commonly used intermediate frequencies

- Television receivers: 30 MHz to 900 MHz

- Analogue television receivers using system M: 41.25 MHz (audio) and 45.75 MHz (video). Note, the channel is flipped over in the conversion process in an intercarrier system, so the audio IF frequency is lower than the video IF frequency. Also, there is no audio local oscillator, the injected video carrier serves that purpose.

- Analogue television receivers using system B and similar systems: 33.4 MHz. for aural and 38.9 - MHz. for visual signal. (The discussion about the frequency conversion is the same as in system M)

- FM radio receivers: 262 KHz, 455 Khz, 1.6 MHz, 5.5 MHz, 10.7 MHz, 10.8 MHz, 11.2 MHz, 11.7 MHz, 11.8 MHz, 21.4 MHz, 75 MHz and 98 MHz. In double-conversion superheterodyne receivers, a first intermediate frequency of 10.7 MHz is often used, followed by a second intermediate frequency of 470 kHz. There are triple conversion designs used in police scanner receivers, high-end communications receivers, and many point-to-point microwave systems.

- AM radio receivers: 450 kHz, 455 kHz, 460 kHz, 465 kHz, 470 kHz, 475 kHz, 480 kHz

- Satellite uplink-downlink equipment: 70 MHz, 950-1450 Downlink first IF

- Terrestrial microwave equipment: 250 MHz, 70 MHz or 75 MHz

- Radar: 30 MHz

- RF Test Equipment: 310.7 MHz, 160 MHz, 21.4 MHz

1.2. Why to regard "immediate frequency downconverter" as an independent device practically?

Although there is no need to have "immediate frequency downconverter" be an independent device, yet immediate frequency downcoverter is practically useful not only to abridge the too long and difficult road for digital radio services to pave but also to revitalize conventional 100K-30MHz radio services sector because as a matter of fact nearly all of the conventional radio boardcast stations and receivers are not designed and equipped with such a special schematic and feature to utilize digitalized multimedia program boardcast using bandwidth between 100kHz to 30MHz, or conventional audio boardcast before massive popularization of digital radio services. By using such a simple schematic of "immediate frequency downcoverter", an industry sector survives from a tragedy of eversleep, hundreds of billions of radio workers worldwide and of radio facilities worthy over trillions dollars are saved from eversleep, making further use of invested investments and creating more GDP, .... Immediate frequency downconverter is an independent device practically.

1.3. What is "immediate frequency downconverter"? Digital Radio Mondiale (DRM) is the digital radio standard for the long-, medium- and short-wave ranges. The standard was formed by a consortium in co-operation with the International Telecommunication Union (ITU). The system offers the radio stations and new service providers access to the multimedia age with small bit rates for large target areas and long distances. For more information visit www.drm.org.

The bandwidth of a DRM bandpass signal is less than 20 kHz and the number of carriers used in the OFDM-modulation is relatively small (max. 460). These features motivate a real-time software implementation of a DRM-receiver on a conventional personal computer (PC) using the sound card as the input and output device. A long, medium and short wave front-end with an intermediate frequency (IF) between 5 kHz and 15 kHz is used to receive the DRM signal. Any commercial front-end with an IF of 455 kHz should be usable by adding a 455 kHz to 12 kHz adaptor (assumed the receiver bandwidth is sufficient for a DRM signal). Documentation of receiver modifications for DRM reception can be found at www.drmrx.org.

This software project implements a working software receiver with, at least, the basic features. Since this project was created at a university and the fundamental idea of such an institution is to teach and stimulate the creativity, this source-code is free under the GNU-General Public License (GPL). Dream is a development project which uses the open source model to improve DRM technology. The main aim of this project is to implement and test new research results on an existing system, whereby the synchronization and channel estimation is of special interest.

The programming-language is C++. The code runs under Mac OSX, Microsoft Windows and Linux. Start of the project was June 2001.

Although this software is distributed as free software under the terms of the GPL this does not mean that its use is free of rights of others. The use may infringe third party IP and thus may not be legal in some countries.

The intended audience of the Dream software are people who are interested in how to decode a DRM stream and want to learn from the algorithms used in this software and people who want to help us improving the performance of the receiver and the source code.

If you just want to get the experience of DRM digital sound quality and expect a very stable and optimized receiver performance, we recommend to buy the commercial DRM Software Radio.

DRM Introduction & General Information

==========================

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 iCom R71e has a 455kHz IF and with a down-converter 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!!

Universal downmixer unit from 455 KHz or 10.7MHz to 12 KHz (input of a PC soundcard), designed for modification of existing AM-broadcast receivers to be able of DRM- receiving by use of the Software radio from Frauenhofer Institut für Integrierte Schaltungen and other decoder software.

- Dimensions of the board 20x20x6,5mm;

- Oscillator frequenzy eligible 467KHz; 443KHz or 10.712 MHz.

- Power supply 7-20V.

- Current consumtion < 6 mA .

- Optional crystal 467 or 443KHz instead of LC;then 8.5mm high. At 10.712MHz only crystal operation.

- Recommended value of output signal voltage: 25-50 mV r.m.s, not more than 100 mV r.m.s

- (DRM-Signal), mixer gain adjustable.

- Input Impedance 2-4.5KOhms depended on adjusted mixer gain.

Schematics circuit, prototype, and ...