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One of the reasons the whole modulation business is so important is during RF troubleshooting with a high quality spectrum analyzer.

When we use many software programs, warnings are given when we exceed parameters. Yes, that's OK or no that's not.

A spectrum analyzer is one of the most complicated pieces of test instruments around. Depending on the settings, entirely different views of a signal can be given with no indication whatsoever of which "picture" is correct. Settings such as sweep rate, video bandwidth, video averaging, resolution bandwidth etc are critical. This is why physical layer RF interference can be very hard to pin down if the correct settings are not applied. We also need to know what shape the modulated signal has [ it is not the square shape as described previously ].To make matters worse, 802.11 has overlapping channels, making things even more confusing. Depending on output filtering and power levels, even the "sacred" 1,6 and 11 channels can have some degree of overlap at the outer sideband areas. When my fingers have recovered, I'll put down some notes about what really happens in modulation and why the 802.11 signals have those strange "bits" [ sidebands ] on them. I'll then put some notes down about how an analyzer works and how to use it properly.

Dave