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Digital Radio Digital radio broadcasts will finally start in Adelaide, Brisbane, Melbourne, Perth and Sydney on 1st May with 71 radio stations (ABC, SBS & commercial) on ten DAB+ transmitters. This is the first of a series of articles giving you the details on this complex and completely new radio broadcast medium. D igital radios will have excellent sound quality and a lot of features that are not available on the existing radios we have listened to over many decades. For example, to select a station you will pick its name from a list. There will be no need to tune across a band. If you are in a car and move out of digital signal range, the receiver will automatically select another digital, FM or AM signal containing the same program. When you move back within range, the receiver will automatically switch back to the digital signal. Timeshift will be available so you can delay listening to broadcasts, just as you can right now with TV if you have a suitable recorder. And while many existing radio programs can be downloaded as Podcasts, most digital radios will have flash RAM cards to store programs. 12  Silicon Chip So you will be able to timeshift, “rewind” and pause the programs while recording and “fast forward” after the recording is complete. And just as digital TV has an electronic program guide (EPG) so too will digital radio. EPG will allow automatic recording of programs within the radio. Other features • Dynamic Label Segment (DLS) DLS will show text information on a screen. This could be telephone numbers, website addresses, tracknow-playing and announcer names. A maximum of 128 characters can be displayed at a time. • Multimedia Object Transfer (MOT) Slideshow This will include product shots, studio web cams, weather maps, album cover information, stock market graphs, racing information and just about any information that can be conveyed as a simple graphic image. A 320 x 240 pixel JPEG image can be transmitted every 9 – 15 seconds. • Multimedia Object Transfer (MOT) Broadcast Website (BWS) BWS allows for the transmission of a series of HTML files (along with corresponding graphic images) to receivers that have a built-in web browser. This allows the user to search the downloaded files. If a receiver has a built-in back-channel (for example, a GPRS enabled mobile phone with a DAB+ radio), it could access links that would take it to the outside world. If there are a lot of requests for files then delays will result due to the restricted download capacity. • Traffic Information Traffic conditions will be transmitted to the car navigation system so siliconchip.com.au Is Coming... by Alan Hughes that the driver can be routed around obstructions. The navigation system will need compatible firmware. • Conditional Access DAB+ is capable of controlling who is able to decode the signal. This can enable narrow-casting to specific private audiences and to Pay Radio. This can also apply to data only. Over the air firmware upgrades for particular receivers would need to use conditional access. • Radio for the deaf & hard of hearing 17% of the Australian population (3.6 million people) have a significant hearing loss. The text capability will enable speech to be subtitled. This applies to emergency announcements, news bulletins, current affairs, talks and phone-in programs. The MOT capability (see above) would allow the display of Auslan (sign language) icons. • Multilingual – SBS Radio and Ethnic Broadcasters 1.3 million people do not use English at home and 4.4 million were not born in Australia. The text capability could be used to add English sub- titles to foreign language programs. This could help the foreign language speakers learn to read English and the converse is true. Let us now look at the various types of digital radio broadcasting. Types of Digital Radio • Digital Audio Broadcast DAB+ is transmitted in VHF TV band 3 (containing TV channels 6 – 12) or using the 1.4GHz ‘L’ band. Note that this system is incompatible with the DAB system used in Canada and the UK. A number of countries, including the UK, put nine radio stations on a single transmitter but this produced sound quality worse than FM stereo. • DAB+ is 3.5 times more efficient in compression than DAB and so the sound quality should not be reduced. In addition DAB+ uses Reed-Solomon error correction to reduce the possibility of gaps in the sound that you hear. All new DAB receivers must be able to decode DAB+ in Europe. • DRM (Digital Radio Mondiale) is used throughout Europe and parts of Asia. It uses the AM bands of MF and HF (Short Wave) and in DRM+, the Channel allocations Fig.1 shows the proposed channel allocations for DAB+. All transmitters will have a maximum of 50kW (effec- Satellite Based 1450 1460 1480 1470 – – – – – –– – – – – – – – – – – – – – – – – – – –– – – LA LB LC LD LE LF LG LH LI LJ LK LL LM LN LO LP LQ LR LS LT LU LV LW Ground Based FM band as well. Coverage is from a community to a continent. It’s used by Radio New Zealand International to cover the Pacific Ocean. • HDRadio is a system which adds a digital sound signal to an existing AM or FM broadcast. This does not work as well as those above. This system involves patent rights to the Infinity Corporation and is used only in the USA. DAB+ & DRM do not have system patent rights. • Radio programs on digital TV signals. Examples of these can be found on ABC and SBS digital TV broadcasts. The disadvantage of these program signals is that you need a digital TV receiver to obtain them and they are unsuitable for use in car radios. • Internet radio is available throughout the world. This is not a public system and is subject to internet costs. Internet radio is also unsuitable for wide area reception. 1490 Frequency (MHz) 1500 –– – – –– – – –– – – – – – – – – – – – – – –– – – –– – – –– – – –– – – –– – – – – – –– – – – – 5A 5B 5C 5D 6A 6B 6C 6D 7A 7B 7C 7D 8A 8B 8C 8D 9A 9B 9C 9D 10A 10B 10C 10D 11A 11B 11C 11D 12A 12B 12C 12D 13A 13B 13C 13D 13E 13F Note: Each DAB+ channel can contain up to 9 radio stations’ programs 180 190 200 6 7 8 9 6 7 8 9 5 6 7 8 210 9A 220 10 10 9 10 11 230 12 240 Digital TV Channels Old TV Channels 11 11 MHz 12 European TV Channels Fig.1: channel allocations for DAB+ radio. Fig.1: Channel allocations for DAB+ radio siliconchip.com.au February 2009  13 ANTENNA Analog to Digital Converter PROGRAM MULTIPLEXER Lr Microphones L DAB+ TRANSMITTER AAC+ ENCODER C R Rr STUDIO Continuous sequential switching between nine different radio programs 20 bit Where else is this program simulcast Date and Time Program type Station Identification Station Location Picture and Text PROGRAM ASSOCIATED DATA Paging Traffic Information Conditional Access Emergency Warning Systems Network Switching Commands FAST INFORMATION CHANNEL tive radiated power) using vertically polarised antennas. Note that not all transmitters will be at full power in all directions. This is to avoid interference problems to television reception outside the listening area. City Adelaide Brisbane Melbourne Perth Sydney Hobart Channels 9B, 9C 9A, 9C 9A, 9C 9B, 9C 9A, 9C 12B, 12D Note that Hobart will start in the next round which is yet to be announced. All transmitters are on Broadcast Australia towers except in Sydney where the transmitters are on the Willoughby TXAustralia site. Radio broadcasting history Before going further, let’s briefly review the development of radio broadcasting up to the present. Amplitude Modulation (AM) was invented in 1901. It’s an analog system with a frequency range of 30Hz to 9kHz (or better), however nearly all available receivers restrict the high frequency response to less than 4.5kHz due to their use of rudimentary IF (intermediate frequency) stages. AM is unable to reject noise in the transmission path. The channel width for AM transmis14  Silicon Chip Fig.2: a typical DAB+ transmitter arrangement. The program multiplexer continually switches between up to nine program digital streams which are combined into the one data stream. sions is 18kHz, due to the upper and lower sidebands of the modulation. Frequency Modulation (FM) was invented 1933. It’s an analog system with a frequency range of 30Hz to 15kHz. Multiplexed stereo was added in the 1960s. Provided there is enough signal, noise is well suppressed. The channel width is 200kHz. Despite the number of FM stations, even its future is not assured. The UK, for example, has announced it will switch off FM radio broadcasting in 2020. Digital Audio Broadcast (DAB) was devised in 1987. It’s a digital system which sends the perceived characteristics of the sound. In other words, signal processing and compression is used to reduce the required amount of data for the signal. The frequency range is from 20Hz to 20kHz. The channel width is 1.536MHz which can carry five stereo programs with sound quality equivalent to FM stereo broadcasts. Digital Radio Mondiale (DRM) was devised 2002. It’s a digital system which sends the perceived characteristics of the sound (see above). DRM is capable of “FM stereo” quality sound. The channel width is 18 or 20kHz and contains only one music quality program. DAB+ is an upgraded version of DAB which can carry nine stereo programs per channel. The channel width is 1.536MHz. The Europeans have now mandated that all new radios must be able to decode DAB+ signals. DRM+ is an upgraded version of DRM which extends the transmission frequency range from 30MHz to 120MHz. The channel width is 100kHz. This system would be suitable in the vacated analog TV channels 1, 2 and the FM radio band. Even if AM and FM radio transmission continues as we know it, to receive DAB+ and DRM+ signals all existing radio receivers will eventually need to be replaced with digital radios capable of DAB+ and DRM+ reception. DAB+ transmission In studios and on compact discs, analog signals are converted to digital in the recording process and on playback the digital signal is converted back to analog. Such digital signals are very high quality but require data rates of up to 3 Mbits/second. So much data will not fit into existing radio channels. Many digital recording systems greatly reduce the amount of data required by storing only those parts of the signal which the brain “perceives”. Such digital standards include digital radio, MPEG 2 & MPEG 4 for TV, DVD & Blue-Ray sound, AC3 (Dolby Digital) sound and MP3 & MP4 used in iPod devices. Some of these standards sound very good and can be regarded as almost equivalent to the CD audio while others, such as MP3, can be notably inferior, depending on the sampling rate. Just how good the DAB+ system eventually sounds will depend on many variables, including the quality of the original recordings, the amount of data compression, sampling rate and so on. In the DAB+ system, AES standard digital signals are fed into an Advanced Audio Coding Plus (AAC+) encoder. In addition, program associated data (PAD) is interleaved with the digitised sound signal. Prior to the transmitter input a second switch repetitively and sequentially selects the digital audio signal and its associated PAD from up to nine different programs. For example, the “Government” transmitter will include ABC Local siliconchip.com.au ANTENNA DIGITAL OUTPUT TUNER AND AMPLIFIER DEMODULATOR AAC+ DECODER SPEAKERS MODULATION SELECT DIGITAL TO ANALOG CONVERTERS FREQUENCY CONTROL STATION SELECT MICROPROCESSOR CONTROL AND DATA SWITCHING DRM+/ DAB+/ FM/AM DISPLAY SCREEN Fig.3: here’s the counterpart DAB+ receiver. The microprocessor takes data from the AAC+ decoder according to the selection by the listener. Depending on signal strength, the output may be DAB+, FM or even AM in origin. Radio, Radio National, ABC Classics, JJJ, PNN and SBS. A DAB+ VHF transmitter will convert the combined signal to the transmission frequency and increase the power fed to the antenna near the top of a tower to radiate the signal to the receivers. Fig.2 shows how up to nine different radio programs are combined into the one DAB+ transmission. DAB+ reception In a DAB+ receiver, the signal from the antenna is filtered to select the channel requested by the listener. The signal is amplified and then fed to the demodulator. The demodulator converts IF signal back into the data signal which is similar to the output of the program multiplexer shown above. The same logic circuit can be used to demodulate all broadcast radio systems. If you are tuned to a DAB+ station and provided the signal level is sufficient for good reception, the selected program is demultiplexed and fed to the AAC+ decoder. The decoder output can either be converted back into analog and fed into speakers or the digital output can feed a home theatre amplifier, particularly if 5.1 sound is being broadcast. The microprocessor is also fed with the alternate frequency information from the program-associated data (PAD). The processor will monitor the quality of the DAB+ signal and also monitors the frequencies containing an identical program (ie, from FM siliconchip.com.au and AM broadcasts). A single tuner does this by tuning to the DAB+ and alternate frequencies at a rate which is too high to be noticed. If the DAB+ quality is insufficient, the next option will be selected. When DAB+ reception returns to acceptable levels, the sound signal will be switched back. Fig.3 shows the much-simplified schematic of a DAB+ receiver. Depending on signal quality, you might be listening to DAB+ DRM, FM or even AM. Broadcast Efficiency Channel width is spectrum “real estate” and has an ACMA auctionable price. Effective radiated power is based on actual transmitter power but with the efficiency of the transmitter antenna system factored in. Transmitter power consumption depends on its efficiency and the power of the air conditioning required. At the most inefficient level, AM radio transmits a carrier which contains no program information; all the program information is in the 9kHz sidebands. This is a fixed power which is one-quarter of the power level transmitted with the loudest sounds. The channel width is 18kHz. FM radio uses a channel width of 200kHz, corresponding to the maximum frequency deviation of ±100kHz. DAB+ bandwidth per channel is 171kHz at 2.4% of the FM effective radiated power per program. Next month we give more details of how the DAB+ system works. SC FRONT PANELS & ENCLOSURES Customized front panels can be easily designed with our free software Front Panel Designer • Cost-effective prototypes and production runs • Wide range of materials or customization of provided material • Automatic price calculation • Fabrication in 1, 3 or 5 days New Version 4.0 New functions include dxf import for inner and outer shapes. Linux, Windows, and Mac OS X compatible. 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