I was hoping somebody could help me with understanding the relationship between the bandwidth of a modulated carrier signal (say using QPSK) and the symbol rate(s) you can transmit across a channel. If anyone knows links to helpful visual representations please link them here. Thanks in advance.
Bandwidth is defined by the pulse shape. (Full stop!)
If scaling the symbol rate that you use with a feasible pulse shape impulse response, you'll necessarily have to scale that impulse response, too, thus making bandwidth for a fixed pulse shape proportional to symbol rate.
The possible data bandwidth is determined more by the worst case signal-to-noise ratio over the channel than by the symbol rate or channel bandwidth.
(e.g. as an extreme case, in zero noise you can theoretically use an approaching infinite number of voltage level to encode lots of bits per symbol).
The spectral bandwidth is determined to some degree by the edge rate of the pulse or symbol transitions.