I have the following wave:

enter image description here

I know that it is demodulated by an envelope detector whose source resistance is 0Ohm and its load resistance is 250Ohm. Now, I need to calculate a C capacitor in order that distortion is negligible for frequencies up to and inlcuding the eleventh harmonic. I know, that in order to have a decent envelope detector I must satisfy the following condition: 1/f_carrier <<< R_load*C <<< 1/W, being W the message bandwidth.

The problem I'm facing, is that I cannot find the W value and thus, I cannot find the value of the capacitor.

  • $\begingroup$ I would use the sixth or seventh harmonic of the triangular wave (times the carrier frequency) to estimate the bandwidth. $\endgroup$
    – MBaz
    Apr 7 at 21:09
  • 1
    $\begingroup$ If this is an assignment, then your prof is probably trying to get you to think past the rules of thumb and actually calculate an answer from first principles. Hopefully when they set this problem for you, they also defined "negligible", because my "negligible" might be your "very, very loud". $\endgroup$
    – TimWescott
    Apr 8 at 16:37

1 Answer 1


If the demodulation must include up to the 11th harmonic, and we know the frequency of the first harmonic $f_1$ (which is the fundamental repetition rate of the triangular waveform), then we know the minimum bandwidth of the demodulator to be $11f_1$.

This is the one-sided bandwidth of the baseband signal, extending from DC to $11f_1$.

  • $\begingroup$ That is so helpful. I appreciate it! $\endgroup$ Apr 27 at 11:52

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