I found this PDF – An Introduction to Digital Data Modes. I don’t how current any of the information is, but it looked fairly recent. Of interest to me, was the chart at the bottom showing the frequencies where one is likely to find some digital action.
In playing around a bit more with Fldigi, I have discovered the wonderful tool known as the “Signal Browser” which allows the user to monitor all the QSOs taking place on a slice of the band. It will even filter out “CQs” so you can quickly locate stations calling CQ.
I’ve heard other digital modes, but I haven’t been able to get Fldigi to decode any of them. It’s my fault; I can’t yet tell the difference between the various modes, so I don’t know what mode to set Fldigi to.
Again, I’m just listening/reading right now. I discovered a nice hack on my Mac to monitor the input audio. When I plug my audio cable into my radio and into my computer, it mutes my radio’s audio, even through the headphone jack.
To correct that, I used a tool in the OS X Xcode developer’s kit called “AU Lab” to create a virtual “mixer board” with the line input from my radio, and an output channel to my Mac’s internal audio. It works great! I saved the “mixer” file on my desktop, simply named “Audio Pass-Through” and I can double-click it anytime to monitor my line-in audio.
An added bonus to this method is that I can assign Apple’s digital effects to my input and output sound, giving me another way to tune my radio’s audio. For instance, I can add a dynamic EQ, a high pass, a compressor, etc. as needed.
Once I hook up my Altec Lansing speakers, the computer itself will be a powerful DSP speaker for my FT-847!
Had I been running Snow Leopard, I could have used the developer kit program Audio Monitor, as described in this Lifehacker article.
Alternately, I could have used a physical solution, like an audio Y-splitter.