wireless communication FM modulation

hello , in FM modulation i know that i should choose the carrier frequency more than the message frequency for a well presentation of the modulated signal, my question is, is there any reason else to choose my fc greater than my message frequency? thnx

A general rule (and there are exceptions) for EM radiation is that is affected by features that have sizes the same or larger size than the wavelength of the radiation. As you can see from the chart, the radio bands above have relatively large wavelengths that are not as affected by objects such as building, trees, weather events or other features in the troposphere as the higher frequency radiation. Another general rule for radiation is that the lower the frequency, i.e. the longer the wavelength, the further a signal can penetrate through solid objects or liquids such as sea water. This type of radiation can also travel further distances around the Earth than other types of radiation, for reasons we will discuss later. Therefore HF and lower frequency radiation is the best to use for direct long distance communications


This is the base reason why modulation is done...

The use of high frequencies for carrier waves in communications permits a higher rate of information transfer than could be accomplished with lower frequencies. The higher frequencies have the potential for higher "data density" or "information density" than lower frequencies. As the frequency increases, wavelength decreases, and thus as time moves on we can send more number of EM pulse than in lower frequencies.


---------- Post added at 15:18 ---------- Previous post was at 15:17 ----------

The use of high frequencies for carrier waves in communications permits a higher rate of information transfer than could be accomplished with lower frequencies. The higher frequencies have the potential for higher "data density" or "information density" than lower frequencies. As the frequency increases, wavelength decreases, and thus as time moves on we can send more number of EM pulse than in lower frequencies.

In the case of amplitude modulation, as pictured above, sidebands are generated equal to the carrier frequency plus the modulating frequency, and also the carrier frequency minus the modulating frequency. So, if the carrier frequency were less than the modulating frequency, wouldn't it create a lower sideband of less than 0 Hz? Actually, in that case the "modulating" frequency would more properly be regarded as the carrier.

It is possible to create modulating frequency greater than carrier frequency. And yes, modulating frequency will act as the carrier frequency..... Refer to the link below for an example of FM....

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That was nice and useful @Genovator..
But when the carrier frequency is lower than the modulating signal, does the demodulation change..???

I am not so sure about this, but if the modulated signal is filtered by a rectifier, then it will rectify the carrier frequency into its +ve amplitude, rather than rectifying the modulating frequency. Because the modulating wave is acting like a carrier...
See the image below.....

Consider the carrier and modulating frequency in reverse.... After rectification, the modulating frequency will be deleted to half, and the message will be damaged....



Reference:
AM Diode Detector :: Radio-Electronics.Com
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I am not so sure about this fact.... So pardon me, if I am wrong....