The History Of AM Radio Receivers
In old days, for the radio transmission, there were various means by which radio signals were generated but these signals were limited to only low frequency band. But very soon it was found that by varying and controlling the amplitude of a signal, the information like speech or music can be transmitted in a much more intelligent manner. This thought formed the base for the invention of AM radios. AM radio receivers or simply AM radios were first started during the beginning of the 20th century. Reginald Fessenden did the first broadcast through radio in 1906. Communication was by way of morse code much in the form that a short transmission denoted a dot and a longer broadcast was a dash. This was the only radio broadcast until the 1920's and was used by the military, commercial telegraphs companies and amateur experimenters. Before the start of World War-I, the AM radio receivers were used at small scale. But after a decade, the use of these radio receivers increased. It was in the 1920s when the first time any radio service on AM was commercialized and started. Initially, Quebec was the first commercial broadcaster in the world. Frank Conrad was the first in America to introduce the AM radio receivers and it was introduced in Pittsburgh, Pennsylvania. The technology used in AM radio receivers is simpler than the technology used in FM radio receivers. In AM radio receivers, signals are sent and received by using amplitude modulation. Amplitude modulated radio transmission is the oldest and simplest form of modulation. In AM radios, the amplitude of the carrier wave is made to vary corresponding to the fluctuations of a sound wave, a television image, or other information, which is to be conveyed. The signal is varied with respect to its amplitude. The radio waves are detected by the AM radio receiver at particular frequency. AM radio receivers are also used to receive the shortwave and medium wave signals during day as well as night time. However, a good AM radio receiver should have essentially enough automatic gain control, which is nothing but a kind of adaptive system found in electronic devices.
However there are three major disadvantages of AM radio recievers. The first limitation is that due to the amplitude modulation technique used in AM broadcasting, the AM radio recievers are not able to decode the original signal from the received signal and there is always static and spurious noise present in the received signals because amplitude modulated waves are easily affected by the electromagnetic waves present in the space. The result is that the listener does not get the good sound quality in AM radio receivers. The second limitation is that AM radio receivers cannot be used to receive signals of wide frequency spectrum. The third is that, the AM signals are easily disturbed in urban areas because of concrete bridges, tall buildings, traffic signals etc, so the AM radio recievers do not work efficiently. This is the only reason that on the great part of the world, AM radio receivers have lost their dignity and dominance. Some of the AM radio receiver manufacturers are: china andy electronics, chit shun enterprise co. ltd., comrex corporation, dongguan richtop electronic co. ltd., potomac instruments, inc. etc. |
