Digital signal consists of many sine waves. Now the signal with waves of frequencies 1Mhz to 5Mhz has bandwidth of 5-1 = 4Mhz. Now the fundamental period of this signal is decided by lowest frequency that is 1Mhz. So one cycle sends 2 bits let's say, therefore 2 bits are transmitted in 1/1Mhz = 1 μs. Hence 1 bit in 0.5μs. Hence bitrate is 2Mbps.

If I increase bandwidth, from 4 to 8Mhz, for the same, does the spectrum still vary from 1Mhz to 1 + 8 = 9Mhz ? because this way by doubling bandwidth and using same lowest frequency, data rate will be same. Unless i increase bandwidth as well as increase minimum frequency. also by doubling bandwidth is it that the range also shifts towards right? eg for bandwidth 4mhz, spectrum was 1 to 5, for 8mhz bandwidth spectrum becomes 2 to 10 or how does it work?

Please explain. I'm a beginner in this and currently going through William stalling's data and computer communication book which states bandwidth increases with data rate and vice-versa where as I feel it's just lowest frequency of bandwidth thats increasing the bitrate or data rate.

  • can someone refer a source to help me understand the concept behind signals and bandwidth ? Commented Sep 14, 2016 at 14:40
  • Paste your question in the physics or electrical engineering SE for a proper answer. Commented Sep 14, 2016 at 15:35
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1 Answer 1


Bandwidth increases as a result of using higher modulation frequencies, not the other way around. Bandwidth is a function of the modulation frequency. So if that is constant, so is your bandwidth.

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