I'm taking a university course in telecommunications (textbook) and I have a number of technical questions regarding technologies such as multiplexing, flow control, frame relay, ATM, digital/analog modulation, encoding techniques [QPSK, BPSK, QAM]. SO doesn't seem like the right place to ask such questions.
Any recommendations for more appropriate sites?
Well, have you considered putting together a study group that invites the professor or graduate students to it on a regular or semi irregular basis? This may be the best approach and would likely assist several people in the same class or program.
SO is quite implementation driven, so if your question is very specific and programming related it's ok, otherwise you'll likely get downvoted and closed.
If you are stumped implementing an ATM in Haskell or what not SO community can probably help.
This is where you'll want to go:
I realised the same as you did, but I use C# for implementing some of the stuff I create so SO is still a nice resource for me :)