Why AM & FM Broadcasts at Certain Frequencies?

In summary, the frequencies used for AM and FM broadcasts are mostly chosen based on historical factors and the trade-off between signal strength and noise. AM frequencies likely take advantage of extended range and manageable antenna size, while FM frequencies utilize a better signal-to-noise ratio.
  • #1
fran1942
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0
Hello, looking at the attached graph of noise voltage to frequency, I am trying to understand (from a noise point of view) why AM and FM broadcasts at the frequencies they do ?

Can anyone offer any suggestions please ?

Thank you.
 

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  • #3
Everything is a compromise. AM frequencies were probably chosen to exploit the extended over the horizon range provided by bending and reflections, while keeping to a manageable antenna size.
 
  • #4
FM has a better signal to noise ratio, so it looks like it is in a place with higher noise (to make use of its resilience toward noise -- it would be a waste to use it between 1k to 10M). AM seems situated in the dip since it isn't particularly resilient against noise.
 
  • #5


There are a few factors that contribute to the choice of frequencies for AM and FM broadcasts. One of the main considerations is the availability of the frequency spectrum. The government allocates certain frequencies for broadcasting purposes, and these frequencies are limited. Therefore, broadcasters have to choose from the available frequencies, and they often select those that are most suitable for their specific needs.

Another factor is the propagation characteristics of the frequencies. AM broadcasts typically use lower frequencies, which have longer wavelengths and can travel longer distances. This makes them ideal for broadcasting over large areas. On the other hand, FM broadcasts use higher frequencies, which have shorter wavelengths and are better suited for broadcasting in urban areas with many obstacles that can disrupt the signal.

Furthermore, the choice of frequencies for AM and FM broadcasts also takes into account the amount of noise present at different frequencies. As seen in the graph, there are certain frequencies where the noise voltage is lower, making them more suitable for broadcasting as they will have less interference from external sources. This is why AM broadcasts are usually found in the range of 535 to 1605 kHz, while FM broadcasts are in the range of 88 to 108 MHz.

Overall, the choice of frequencies for AM and FM broadcasts is a result of various technical, practical, and regulatory considerations. It is important for broadcasters to carefully select the frequencies that will provide the best quality and reach for their audience.
 

1. Why do AM and FM broadcasts use specific frequencies?

AM and FM broadcasts use specific frequencies because they have been allocated by the government for radio broadcasting. These frequencies are carefully chosen to avoid interference between different stations and to optimize the transmission of signals.

2. What is the difference between AM and FM broadcasts in terms of frequency?

The main difference between AM and FM broadcasts is that they use different frequency ranges. AM (Amplitude Modulation) broadcasts use frequencies in the range of 535 to 1705 kHz, while FM (Frequency Modulation) broadcasts use frequencies in the range of 88 to 108 MHz.

3. Why are AM and FM broadcasts at different frequencies?

AM and FM broadcasts are at different frequencies because they use different methods of modulating the carrier wave. AM modulates the amplitude of the wave, while FM modulates the frequency. This results in different frequency ranges being used for each type of broadcast.

4. How do the frequencies used for AM and FM broadcasts affect the quality of sound?

The frequencies used for AM and FM broadcasts have a direct impact on the quality of sound. AM broadcasts are more susceptible to interference and noise, which can affect the quality of the sound. On the other hand, FM broadcasts have a wider frequency range and are less prone to interference, resulting in better sound quality.

5. Are there any other factors that determine the specific frequencies used for AM and FM broadcasts?

Yes, apart from government regulations, there are other factors that determine the specific frequencies used for AM and FM broadcasts. These include the availability of frequencies, the power of the transmitter, the geographical location, and the target audience of the station.

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