Definitely inc on-board audio, and being the sort of person that likes to have his cake and eat it 2
... how do you feel about stereo! (Or actually prefer 2 x mono... nothing like the separation of individual sound channels)
By all means shoot me down if you don't agree with my reasoning. I'll explain...
Having an 'ear in the air' can help a lot (I believe anyway) for diagnostic purposes, especially for me being an absolute noob. I really don't want to go thru years of learning that others have had to come by the hard way... experimenting with this, that and the other... then test it again. What the motor sounds like under changing loads, especially I.C. engines... all new to me. When a motor/drive train is playing up, I want to hear it.
Maybe even helpful to have a mic switched on wherever the model is when it's time for that walk of shame! eg. can you hear traffic noise, or wind in the trees, or water...
When I deploy on-board camera for aerial photos it would be nice to hear that sound produced by some cameras that mimic the click of a mechanical shutter... feedback that a photo has been taken is what I'm getting at.
From time to time it could be advantages to listen to the sounds around the model, possibly needing some active noise cancellation but I think it could be done. Sounds of nature, automobile traffic etc. It may be advantageous to NOT go get your model if you can hear somebody yelling obscenities at it! - like an angry farmer?
Anyway, enough of the case to have an on-board mic...
I like the MyFlyDream tracker as the basis for a base station. Especially the 12 slip-ring version... room for expansion! As I understand it, it has to get it's GPS data down-linked over an audio channel. I can't see anyway around this. If I'm missing something, please put me right.
With 1 audio channel already taken for the tracker, none of what I wrote above can be put into effect without a second channel.
Finally Bruce, I see that more powerful tx's are available now, such as "600mw 5.8G video Tx" at BEVRC. Can your backpack supply enough power to cover that, as it's only a matter of time before somebody will want to do it?
So there... my 2c's worth. -