Long live radio

“Radio is dead! Long live radio!” That is how my interview with Dave Cherry started when talking about DAB+, an advanced digital radio technology that is currently being trialled in Johannesburg and Pretoria.

The trials are to the delight of many owners of cars fitted with DAB+ receivers, have portable DAB+ radios or who have downloaded the necessary software and have a dongle that will tune the frequency the DAB+ trial operates on. Dave Cherry is part of the consortium involved with the trial.

His interest in DAB and DAB+ goes back to when he was technical manager at Classic FM when the station could not get an additional FM frequency in Pretoria and was looking at DAB+. Dave, now retired, is still very active with the trial.

DAB+ is a digital sound standard broadcasting system designed for operating in band III (VHF and L band). DAB+ is an enhanced of DAB with MPEG 4 AAC+ (advanced audio coding) and equal error protection added as additional features.

AAC is an audio coding standard for lossy digital audio compression, designed to be the successor of the MP3 format. AAC generally achieves better sound quality than MP3 at similar bit rates. Although only 2 dB gain is achieved in the coverage area, DAB+ can accommodate three times as many channels per DAB+ multiplex (MUX)

The DAB+ technology is an alternative or a supplementary technology to relieve congestion in the current FM band. Currently, several popular FM radio stations have poor coverage in Pretoria because there are no free channels available there in the FM band. Similar problems are experienced in the Western Cape.

Also, South Africa adopted a 100 kHz separation between FM stations, compared to 200 kHz in other parts of the world. In some areas this causes cross channel interference. DAB+ solves these problems as it offers more channels and reduces adjacent channel interference. There are many benefits the DAB+ technology offers, just to list a few:

  • Good quality service because of AAC with quality not directly related to the RF signal in the planned coverage area.
  • It is very cost effective as up to 24 different stations can be accommodated on one multiplex, requiring only one transmitter for each planned coverage area.
  • Enhanced user experience as DAB+ offers additional functionality such as electronic programme guide, news feeds and images.
  • Single frequency network allows more efficient use of limited spectrum with more transmitters at different locations providing larger coverage on the same frequency.
  • Capable to operate in simulcast mode broadcasting analogue and digital simultaneously which could assist during analogue to digital migration.
  • Includes hand-over capabilities between different radio platforms such as DAB+ and FM and vice versa.

The current trial started on 15 March 2019. The license was obtained on behalf of the National Association of Broadcasters (NAB) and the radio industry by the SABC. Two transmitters are operating, one in Johannesburg on the Brixton Tower and the another one in Pretoria operating in Band III on channel 13f at 239,2 MHz.

The two stations operate in a single frequency network (SFN). The Pretoria transmitter runs at 10 kW while the power of the Johannesburg transmitter was reduced to 5 kW as at the 10 kW level it was interfering with one of the analogue TV stations.

Unlike FM, DAB+ uses reflections to its advantage while on the current FM service signal reflection from buildings and surrounding terrain causes signal distortion.

Two phases of the trial have been completed. Phase three of the South African DAB+ trial went on the air on 15 March this year and will run for eight months with an extension of six months, which means that the current two transmitters and stations will go off the air in May 2020.

The current MUX can accommodate 24 radio stations, of which a third of the capacity has been allocated to community-based radios stations. There is no cost involved in being part of the trial other than that the stations are responsible for delivering their signal to the Brixton tower.

“It is interesting that when ICASA officials visited a number of countries to study the way DAB+ was introduced, the Australian interaction planned for two hours lasted five hours,” Dave Cherry said. “Australia is one of the countries where DAB+ is operating very successfully and expanding all the time.

Although a smaller population than South Africa, their topography is very similar to ours. The Australians advised South Africa never to switch off a trial. We believe they are right. We experienced eight months switch off between the last and current trial.

During that period the equipment was unattended. For the previous trial we were using a borrowed MUX which had to be returned. We had to switch back to the original purchased MUX which used the Dolby system.

Dolby was sold and it appeared that the manufacturers of the MUX had not updated the software. On our request, the company updated the software which we loaded on our system. A new codec became available from Fraunhofer. Their system is superior and renders better audio quality, however our budget did not allow the switchover but after further negotiation we obtained two licenses. We are now alternating two services on a monthly basis using the Fraunhofer codec and are recoding the results.”

The quality of the audio also depends on the bitrate. The “sweet spot” is 64 kbit with 40-bit sampling while some stations use 48 kbit.

Internationally, DBM+ and related digital systems are supported by WorldDAB , the global industry forum for digital radio, facilitating the adoption and implementation of broadcast digital radio based on DAB / DAB+.

WorldDAB delivers tailored solutions and advice on all aspects of the switch from analogue to digital radio including regulation, licensing, technical trials, network build out, marketing and production of new digital radio content.

When South Africa will introduce DAB+ in parallel to FM is an open question as currently the country is still struggling to sort out its digital migration of the terrestrial TV services, now many years behind the agreed ITU switch off date.

Every new Minister of Communication has made promises but that is where it remains, just promises. DAB+ will just add so much more to one’s listening pleasure and will solve the shortage of channels. It also offers the opportunity to establish new channels catering for so many more genres of music and content.

Source: EngineerIT

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Long live radio