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As known, Bandwidth is the difference between the upper and lower frequencies in a continuous band of frequencies. OK, what means when saying that bandwidth range is 15 ~ 20 KHz ? Does that mean that the bandwidth should be 5KHz ?

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Range is the minimum to the maximum value of something. Since bandwidth is the difference between the upper and lower frequencies in a continuous band of frequencies, then the range of bandwidth of 15 to 20 KHz would then mean that the minimum difference (bandwidth) would be 15 KHz and the maximum bandwidth would be 20 KHz. If the saying was instead that the range of occupied frequencies was 15 to 20 KHz then it would then mean the bandwidth was 5 KHz.

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  • $\begingroup$ Thank you .. So base-band bandwidth = 10 KHz means that pass-band bandwidth of 5 KHz which means we can say the bandwidth range , for example, is 15 ~ 20 KHz. Am I right ? $\endgroup$ – Fatima_Ali May 25 at 3:06
  • $\begingroup$ @Fatima_Ali base-band bandwidth for real signals only can typically be shown just from DC (f=0) to the band edge. When this signal is moved to passband this is doubled as DC would be moved to the carrier and the bandwidth would extend to the band edge on both sides of the carrier. However complex signals would need to be double sided even at baseband. It is always best to declare if the double-sided or single-side bandwidth is being used. That said a 10 KHz base-band bandwidth that is double sided would be 10 KHz at passband. $\endgroup$ – Dan Boschen May 25 at 13:17
  • $\begingroup$ A signal that has a range of double-sided bandwidth at baseband would have that same range of bandwidth at passband...range meaning the bandwidth could be ast low at 15 KHz or as high as 20 KHz. $\endgroup$ – Dan Boschen May 25 at 13:17
  • $\begingroup$ Oh, come on, Dan! You know perfectly well that a baseband bandwidth of 10 kHz means that the (two-sided) spectrum of the signal is confined to $[-10^4, 10^4]$ Hz and this signal is not referred to as a signal of bandwidth of 20 kHz) while a passband signal of bandwidth 5 kHz has (two-sided) spectrum that is confined to $[f_c-2500,f_c+2500]$ Hz and to $[-f_c-2500,-f_c+2500]$ where $f_c > 2500$. Why are you creating a new notion of double-sided bandwidth? $\endgroup$ – Dilip Sarwate May 25 at 16:13
  • $\begingroup$ @DilipSarwate It's not my new notion (for example see: sjsu.edu/people/burford.furman/docs/me120/FFT_tutorial_NI.pdf) I think the reason to clarify is for the case of complex baseband signals, where you could have a baseband AND passband bandwidth of 10 kHz, in the case that the signal is confined to the postive half spectrum. But if we did have a real baseband bandwidth of 10kHz extending from DC to 10kHz we would indeed have a passband bandwidth of 20kHz. I prefer to not treat DC as being different from any other carrier and use the two-sided spectrum everywhere. $\endgroup$ – Dan Boschen May 25 at 16:21

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