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AM Radio Circuits

  

AM radio began with the first, experimental broadcast on Christmas Eve of 1906 by Canadian experimenter Reginald Fessenden, and was used for small-scale voice and music broadcasts up until World War I. AM radio technology is simpler than Frequency Modulated (FM) radio, Digital Audio Broadcast (DAB), Satellite Radio or HD (digital) Radio. An AM receiver detects amplitude variations in the radio waves at a particular frequency. It then amplifies changes in the signal voltage to drive a loudspeaker or earphones.

The earliest crystal radio receivers used a crystal diode detector with no amplification. Medium-wave and short-wave radio signals act differently during daytime and nighttime. During the day, AM signals travel by groundwave, diffracting around the curve of the earth over a distance up to a few hundred miles (or kilometers) from the signal transmitter.
However, after sunset, changes in the ionosphere cause AM signals to travel by skywave, enabling AM radio stations to be heard much farther from their point of origin than is normal during the day. This phenomenon can be easily observed by scanning an AM radio dial at night. As a result, many broadcast stations are required as a condition of license to reduce their broadcasting power significantly (or use directional antennas) after sunset, or even to suspend broadcasting entirely during nighttime hours. 
 
Because of its susceptibility to atmospheric and electrical interference, AM broadcasting now attracts mainly talk radio and news programming, while music radio and public radio mostly shifted to FM broadcasting in the late 1970s. However, in the late 1960s and 1970s, top 40 rock and roll stations in the US and Canada such as WABC and CHUM transmitted highly processed and extended audio to 11 kHz, successfully attracting huge audiences. Early experiments with stereo AM radio involved two separate stations (both AM or sometimes one AM and one FM) broadcasting the left and right audio channels.
 
This system was not very practical, as it required the listener to use two separate radios. Synchronization was problematic, often resulting in "ping-pong" effects between the two channels. Reception was also likely to be different between the two stations, and many listeners used mismatching models of receivers.
 
 

Circuits




Hi Guys, Just meddling with AM radio construction and got the resonator circuit to provide the frequencies of approx. 540 - 1610 kHz, my next task is to...

This video covers the history of the discovery of radio waves, to the creation of simple oscillator based radio transmitters. Then I explain what modulation and amplitude modulation are, and show y...

Summary notes and reviewer in Chapter 5: Amplitude Modulation Reception from the book "Electronic Communications System" by Wayne Tomasi. The notes are properly synchronized and concise for better ...

... and the US known as KDKA. Nowadays, AM radio is mainly used for talk programs, news and sports and not music broadcasting, since the AM signal is susceptible to electrical or atmospheric interf...

In this circuit FM modulation is used. In FM modulation, frequency of the carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal. Normal FM radio will use th...

Basic help can be found in the Electronics Primer. How. ... Although the circuits used in radio stations for AM broadcasting are far more complicated, this nevertheless gives a basic idea of the co...


AM Modulation and Demodulation Part 1


Amplitude Modulation (AM)


Amplitude Modulation tutorial and AM radio transmitter circuit


Lecture - 8 Amplitude Modulation