The Beginning of Radio Communication

Photo © Eugene Brennan

From one of the old books that belonged to my grandfather. A note in the appendix of a volume of the ICS reference library, 1905. If only they knew the developments that were to come in the future! In modern parlance, "the high-frequency transmission wave" is known as a carrier and the modification of the carrier by the superimposed wave is known as modulation. Sound waves having frequencies in the audible spectrum can't just be converted to an equivalent radio signal and transmitted. The frequency would be too low and for various technical reasons, including providing sufficient bandwidth for other channels broadcasting on and sharing the radio spectrum, and minimizing the size of antenna required, a technique called modulation is used. This is commonly either either amplitude modulation (AM) or frequency modulation (FM). The carrier is varied by a modulating signal derived from e.g. an amplified signal from a microphone, which changes the carrier's "size" (amplitude) or frequency. Originally, carriers were low, in the hundreds of kHz or somewhat lower. Carrier frequencies nowadays are vastly higher, typically 5 gigahertz (GHz) for WIFI and up to 108 MHz for normal radio broadcast programs on the FM band.

Photo © Eugene Brennan