Russia: DRM in shortwave offers unique potential for national coverage

Russia: DRM in shortwave offers unique potential for national coverage

Victor Goreglyad, Deputy General Director–Director of Department for Radio Broadcasting and Radio Communication, has summarised the results of recent DRM studies undertaken in Russia. One of the conclusions is that digital radio broadcasting using the DRM standard ensures greater coverage with a better quality of audio content whilst using less transmitter power when compared with traditional AM radio broadcasting..

In 2012 the Russian television and radio broadcasting network conducted a number of tests to further the work on the study of the performance of transmitters in the DRM standard.

A test zone was created in Moscow, and these tests not only measured the signal reception in different conditions, including inside buildings, but also studied the options for building local synchronous networks for DRM digital radio broadcasting in big cities, within the 25,67 – 26,10 MHz range.

The noise levels and level of fading were evaluated and included measurements taken in built-up city areas as well as inside buildings. The signal/noise ratio required for decoding for different noise-resistance regimes was defined. The required field strength and transmitter power capacity was also determined.

Practical recommendations for building local synchronized networks for DRM digital radio broadcasting in big cities have also been developed. 26MHz digital radio broadcasting was compared with UCV range FM broadcasting.

The results from the test studies and the analysis of measurement findings confirmed the possibility of creating SW range synchronous networks and the expedient use of 25, 67 – 26, 10 MHz frequency range in large urban areas. This work continues the research currently underway on the DRM standard SW radio broadcasting synchronous networks.

A zone of synchronous networks was created in the Moscow area. It made use of two transmitters located in Krasnodar (30 kWt) and Kaliningrad (15 kWt).

The research, was aimed at increasing the efficiency of DRM standard radio broadcasting networks, developing practical recommendations for building DRM standard radio broadcasting synchronous networks, as well as minimizing the use of SW range frequency resource. The findings of the research confirmed the reliability of the received signal from the two transmitters mentioned above, as compared to that taken from each separately. The evaluation of synchronous networks amplifying showed a 6 dB -11 dB power gain in certain time intervals.

As a result of this work conducted in the SW range, broadcasting in DRM has offered the potential to ensure quality 24hr reception over a considerable area for the first time in the history of this country.

The results of this study can be used to contribute to the planning and strategic development of radio broadcasting in the Russian Federation.

Based on the results of the research work, in November 2013 the IUC prepared and submitted a document, “The development of the recommendations for organizing single-frequency synchronous DRM standard broadcasting networks on the basis of test zones” to the Administration of Telecommunications of the RF, into the 6th research group of IUC-R: “Tests of single-frequency radio networks DRM in the SW range”.

Key provisions of the report:

 The DRM standard envisages applying of single-frequency synchronous radio broadcasting networks. They have been tried in Berlin in MW range, in West Europe in SW range and in Moscow in the range of 26 MHz.

Despite the successful results of the tests in question, there is no detailed information available in technical reference books on the quantitative parameters characterizing the use of synchronous networks. In particular, there are no maximum network gains, available transmission value etc. 

Thus, the results of tests of the parameters of SW synchronous networks of the DRM standard digital radio broadcasting can be of practical use.

The text of the present work has contributed to the draft of a new report on digital systems of audio broadcasting. (Working Document toward a Preliminary Draft New Report ITU R BS. [DSB-Transition] «Implementation considerations for the transition to digital terrestrial sound and multimedia broadcasting»

The third DRM work stream focused on the effect of technical parameters of the digital radio broadcasting transmitter bending tract on the standing wave ration antenna-feeder device, which is essential to work out the recommendations for the choice of radio transmitters able to work in the digital DRM standard environment for narrow-band antenna systems.

When organizing DRM standard digital radio broadcasting in the range below 30 MHz, the signal band can reach 10…20 kHz, but the antenna-feeder device (AFD) should not be below the indicated value.  Broadband characteristics of antenna are difficult to achieve as well as very costly in the long and medium wave bands.

At the same time manufacturers and providers of contemporary radio transmitters, power amplifiers which are based on the method of divided amplification of composing modulated variations (Kan’s method), stress the importance of thorough tuning of antenna (to the min. standing wave ratio of 1, 05…1, 1 at the borders of DRM signal band), in order to ensure the required quality characteristics of the received digital broadcasting signal. Otherwise, unacceptable non-linear deviations occur, leading to extending of the signal spectrum.

The present work has also conducted quality analysis of the work of UMRC for narrow-band antenna, which provided the mechanism for understanding the non-linear deviations. The possibility of decreasing the demands for the antenna traffic band through apparatus capacities, including the installation of de-amplifying chains and FWC-diplexers at the end of the bending tract filter, has also been studied.

On the basis of the whole complex nature of these studies the recommendations for the choice of transmitters able to work for the narrow-band antenna in DRM standard digital regime have been developed.

The aim of the work in question was to create a test area for digital SW radio communications to study the efficiency of the work of antennas of zenith ionizing (AZI) < and included the research and working out of the recommendations for the use of ionizing antennas in the networks of digital radio broadcasting and SW radio communications. The study was conducted with the use of small-power radio transmitters of 100-200 Wt.

On the basis of the evidence provided in the report of the experimental trials in test areas of SW digital radio communications and digital radio broadcasting in SW ranges with the use of ionizing antennas the following conclusions have been made:

•        As a result of the measurements made during the test in the north Russia region, the characteristics of digital radio communications with the units equipped with small-size ionizing antennas revealed that there is a possible and expedient solution in using small-size AZI at subscriber stations. At the same time the head station should be equipped with full-size AZI.

•        The tests revealed that it was possible to transmit short text messages (sms) and e-mails by SW radio-channel of zenith radio waves in data transmission networks.

•        It was shown that by connecting to the telephone networks in general use in duplex regime of work of subscribers of SW digital networks of radio communications, it is possible, with the use of parallel OFDM modems, to temporarily divide the channels and verbal codes at a speed of 1,2 kbit/sec.

•        The analysis of the availability of digital communications and digital radio broadcasting with the use of AZI in different bands showed that on the basis of theoretical calculations and through using transmitters for ionizing antennas that it would be possible to ensure full coverage of the whole of Russia, in different seasons and during different periods of solar activity.

•        Recommendations for the use of AZI by radio communications units and radio broadcasters of RSTC have been worked out.

Materials submitted to the International Union of Radio Communications (IUC)

Based on the results achieved when measuring DRM signal parameters in the MW transmitter digital broadcasting coverage area placed in Psaryki point of residence (works completed in 2012), IUC has prepared and submitted in April 2013 a report for the 6th IUC-R research group:

 “Measurements of DRM coverage area in the medium-frequency band in day-time, night-time and in the feeding”.

Key provisions of the presented report:

Over recent years a number of countries have conducted a study of DRM standard digital audio broadcasting regimes.  Parts of the studies were laboratory based findings, other results did not fully analyze all aspects of the DRM signal reception in different conditions: urban and rural areas, day-/night-time as well as in the feeding zone.

The results of measurements provided in the present report allow us to forecast the minimal field power, the signal-to-noise ratio, the number of decoded audio blocks as well as other parameters that can guarantee high quality reception of the DRM signal in medium-wave range.

The DRM standard digital radio broadcasting system provides broad possibilities for the “exchange” or ‘trade off” between the quality of the transmitted audio content with the geographical range of the coverage area. The results of measurements of the coverage area taken in different noise-resistant regimes allow the broadcasters and network providers to choose appropriate regimes of noise-resistance and to define the quality of service to any given area, or, vice versa, to define which area will be serviced with given quality.

In conclusion, the research conducted has shown that digital radio broadcasting using the DRM standard ensures greater coverage with a better quality of audio content whilst using less transmitter power when compared with traditional AM radio broadcasting.

The text of the present report has been made a part of a new draft report on digital systems of sound broadcasting. (Working Document toward a Preliminary Draft New Report ITU R BS. [DSB-Transition] «Implementation considerations for the transition to digital terrestrial sound and multimedia broadcasting».