ambandwidthfm
If a 5kHz baseband signal is modulating an AM carrier wave, the sidebands will be centered around the carrier wave and the the signal will occupy 10kHz bandwidth. AM radio limits the upper modulating frequency to 5 kHz.
But FM signals require a bandwidth of about 200 kHz for the same baseband signal. Why is that so?
EDIT:
To answer your last question first, you can't have a narrow bandwidth filter around 1MHz and yet still have a fast rise time. If you think about the spectrum of a square wave, it has frequency components extending to infinity. The higher frequency components contribute to the 'squareing up' of the signal and sharpening of the edges. e.g. see http://mathworld.wolfram.com/FourierSeriesSquareWave.html Having a narrow band around 1MHz means your signal will come out looking like a 1MHz sine wave.
With that in mind you have to design a bandpass filter that does not attenuate your 1MHz fundamental frequency too much, yet includes high enough frequencies to give the desired rise time. Following your formula, 0.34 = rise time * bandwidth, you have calculated a bandwidth of 34MHz is required. The next step is to consider bandwidth = high cutoff freq. - low cutoff freq. You want the low cutoff to be less than 1MHz. Let's choose 500kHz. Thus the high cutoff would be 34.5Mhz and the centre frequency 17.25Mhz.
To get rid of the most noise, the filter should have a steep rolloff, e.g. the two filters mentioned in the comments. This means your low cutoff frequency can be very close to 1MHz without too much attenuation, and in the higher end of the spectrum rolls off very quickly after the high cutoff frequency, reducing high frequency noise.
SSB is not how you describe but first regular AM as broadcast by the radio stations. This you appear to correctly describe except for the demodulation which you omit.
In AM the amplitude is modulated but not by so much that the carrier amplitude becomes zero at any point. This is regular AM and for instance a \$1V_{peak}\$ carrier might reach (due to the effects of modulation) peaks of 1.8V and troughs of 0.2V: -
A simple diode detector will demodulate this so this method is suitable for public broadcast radio stations because the radio receiver is simplified by using the diode detector.
Suppressed carrier AM is like regular broadcast AM but where the modulating signal pushes the carrier beyond the limits of broadcast AM. The result of this is that the carrier phase becomes reversed every half cycle of the modulating signal. A simple diode detector no longer produces any decent recovery of the audio signal. Here is a picture of what happens when AM is over-modulated (heading towards a suppressed carrier scenario) and you try and use a simple diode detector: -
Why is it called suppressed carrier - the carrier inverts every half cycle of the modualting wave and if you used a spectrum analyser there is no trace of the carrier despite the resultant modulated carrier being centred at the carrier frequency: -
Recovery of the modulating signal (i.e. the original audio signal) is much trickier and that is why this technique is not used in broadcast transmitters in order to keep receiver cost and/or complexity low.
SSB usually is a further modification to suppressed carrier where one of the sidebands is either totally or partially suppressed in order to create a smaller bandwidth in what is being transmitted - more power can be focussed into the single remaining sideband and with a more complex receiver it can be adequately received. To understand what SSB looks like you have to look at the frequency spectrum of DSBSC (Double sideband suppressed carrier) and imagine it is lopped off on one side: -
Best Answer
They need not, narrowband FM occupies the same bandwidth as AM, for the same audio bandwidth. Transmitted AM bandwidth is fixed at twice the audio bandwidth.
However, wide deviation FM provides signal to noise ratio improvements above that which is possible for AM. It also provides the so-called capture effect, whereby a weak station near to a stronger wanted one is not heard at all, not just merely heard weaker. It's therefore worth increasing the deviation and so transmitted bandwidth of FM to get higher quality (read higher advertising revenue).
The original AM broadcast band is quite narrow and doesn't have the space for wideband FM channels, so FM broadcasting is done at a much higher carrier frequency.