New high-power all-solid-state emitters

As we approach the 21st century, over-the-air sound broadcasting is still a popular means of communication in the long- and medium-wave ranges:

• long wave (OL): 153 to 281 kHz ;

• medium or hectometric waves (OM in French, MW in English): 531 to 1,705 kHz.

Amplitude modulation (AM or A3 E) is the only modulation technique used in these frequency bands. However, it suffers from a number of imperfections, such as a bandwidth limited to 9 or 10 kHz, and high sensitivity to parasites, interference and radio noise. Nevertheless, it is still considered by broadcasters as the only operational means of reaching the greatest number of listeners on a regional or national scale.

This interest is simply due to the existence of over two billion AM receivers worldwide. Today, these receivers are relatively inexpensive. Based on envelope detection, they are technically very simple, easy and convenient to use. They don't require any special antenna installations, and provide good reception in a wide range of conditions, even inside buildings.

On the transmitter side, over 175,000 transmitters worldwide ensure program transmission. Although their average lifespan often exceeds 25 years, existing transmitting equipment needs to be renewed to continue providing service in good conditions.

High-power transmitters are undergoing a major technological shift. Vacuum tubes (triode, tetrode) modulated by anode voltage are now being replaced by fully transistorized transmitters using modulation strategies based on digital signal processing.