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In QAM (Quadrature Amplitude Modulation) theory what is the relationship between the modulation frequency and the carrier frequency called?

It is often stated in QAM tutorials that the carrier frequency must be "much larger" than the modulation frequency. A common statement is that the carrier frequency must be ">100 times the modulation frequency". It seems obvious to me from a practical standpoint that you must impose a certain minimum number of modulation frequency cycles onto the carrier in order to have any hope of demodulating the signal at the receiving end of a link. So, as an extreme case you would not modulate the carrier at the carrier frequency as this would produce nominally only one cycle of the received carrier signal which must be processed by the demodulator. Much better to have, for example, 100 cycles of the carrier signal for the demodulator to process.

To be sure, my question is not what numeric value is required, but rather what is this characteristic or operational parameter of QAM called in the QAM literature?

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  • \$\begingroup\$ It is primarily the relationship of bandwidth to centre frequency as this determines the effective circuit Q factor required at the receiver. \$\endgroup\$ – Peter Smith Jul 12 '16 at 9:55
  • \$\begingroup\$ Peter, is there a formal equation or methodology which relates center frequency to bandwidth? \$\endgroup\$ – FiddyOhm Jul 12 '16 at 11:14
  • \$\begingroup\$ FiddyOhm - not that I am aware of - the relationship is application dependent. \$\endgroup\$ – Peter Smith Jul 12 '16 at 17:03

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