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Master1022
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- TL;DR Summary
- How are the two carrier frequencies for FSK modulation chosen?
Question:
For frequency shift key modulation in the binary case, how are the two carrier frequencies chosen?
From online reading, I have seen that the carriers are chosen to be different but also with the goal of minimising bandwidth and without any overlaps of the spectra, etc.
However, I have been told by a tutor that we ought to choose one carrier frequency and then multiply that value by one of the amplitudes of the wave to get the other carrier. However, I have looked on the internet (where I cannot find much clear information about this) and cannot find any source to support this statement. This suggestion runs into issues when there is a 0 amplitude (perhaps an offset would fix that) and a -1 amplitude, the latter of which leads to a case where the two carriers aren't distinct and the frequency spectra would overlap?
For example, if we had a pulse signal that was +1, -1, +1, -1, +1, -1, ... and we wanted to modulate it onto a cosine wave then, according to this suggestion, the points where the pulse changed levels would not lead to any difference in the cosine wave as ## cos(\omega_c t) = cos(-\omega_c t)##. Choosing two distinct carrier frequencies seems to make more sense to me in such a scenario.
I would appreciate any guidance and/or clarification regarding this topic.
For context, I have only been exposed to these concepts at an introductory level (i.e. undergraduate)
Thanks.
For frequency shift key modulation in the binary case, how are the two carrier frequencies chosen?
From online reading, I have seen that the carriers are chosen to be different but also with the goal of minimising bandwidth and without any overlaps of the spectra, etc.
However, I have been told by a tutor that we ought to choose one carrier frequency and then multiply that value by one of the amplitudes of the wave to get the other carrier. However, I have looked on the internet (where I cannot find much clear information about this) and cannot find any source to support this statement. This suggestion runs into issues when there is a 0 amplitude (perhaps an offset would fix that) and a -1 amplitude, the latter of which leads to a case where the two carriers aren't distinct and the frequency spectra would overlap?
For example, if we had a pulse signal that was +1, -1, +1, -1, +1, -1, ... and we wanted to modulate it onto a cosine wave then, according to this suggestion, the points where the pulse changed levels would not lead to any difference in the cosine wave as ## cos(\omega_c t) = cos(-\omega_c t)##. Choosing two distinct carrier frequencies seems to make more sense to me in such a scenario.
I would appreciate any guidance and/or clarification regarding this topic.
For context, I have only been exposed to these concepts at an introductory level (i.e. undergraduate)
Thanks.