21 Oct AM & DRM30 – The Most Economical Way to Cover Large Areas
Most countries in the world operate medium wave transmitters using output power of above 500kW. The aim of the medium wave broadcast is to achieve basic radio propagation for wide range areas and to influence neighbouring countries. In several European and North African countries longwave transmitters, which are high powered above 300kW and up to 2MW, are in operational use.
At the moment there is no alternative technology available for large area. Satellite and cable networks are vulnerable and all the most modern digital technologies like DMB, DVB and DAB are physically limited in coverage by the used frequencies; they also reach only relatively small areas. These technologies, with high network costs, will be mostly used for city coverage with a high population or in countries with a well-established general infrastructure and large propagation networks.
On the other hand, one has to see that AM is a widely acknowledge technology; well-known and established worldwide for nearly 100 years with a huge amount of receivers available in all countries. The AM standard has never changed, so each and every AM radio receiver in the world can be used to receive AM stations. This is a big advantage in disaster or emergency situations, as the whole population can be reached at minimum cost and effort.
A new and very interesting opportunity presents itself with the advent of the DRM standard. With DRM the broadcaster can use the large area coverage benefit given by AM transmissions and all the advantages of modern digital radio technology at a fraction of the analogue energy costs. DRM offers at least the same coverage as before with AM with sound that is free of interference and crystal clear. Additionally many new features such as Journaline or Emergency Warning are available.
A good example is the 1.000kW AM transmitter. Due to the physical conditions and, importantly, the crest factor of the DRM signal, it reaches the same coverage with only 200kW DRM output power.
New AM transmitters with intelligent DRM modulators get up to 80% DRM power out of their analogue carrier, so, for example, the installation of just 250kW AM power would be sufficient.
This simple calculation shows that with plenty of reserve, a quarter of the analogue transmitter power would be sufficient to get the same coverage in AM but with a significant improvement in quality and extra features on top.
If an old valve- type transmitter was to be replaced in the same conditions the power savings would be higher. The new solid-state transmitters of almost all manufacturers reach about 90% over all. Efficiency can be compared with the 60 to 70% of the latest generation valve-type transmitter. This is another huge step forward for the green DRM technology and should demonstrate the importance of AM and DRM technology for modern radio propagation.
Dipl. Ing. Jochen Huber
President, JHBC Broadcast Consulting
Honorary Member, DRM consortium