Hello Matt!
I know that the current documented thinking is to have two SDX's and no analog transponder, however we did say we'd bring up for discussion at a telecon prior to the Symposium. I know that this was brought up in July 2005 where it was clear that the answer to the members was yes, we'd have a backup _analog_ linear transponder.
Why stop there? We should have a backup to the analog transponder in the form of a CW transponder. Then we can back that up with a spark transponder. Finally, we should have some sort of semaphores or smoke signals to back that up.
We tried smoke signals with AO-40. The results weren't pretty...
We've flown analog transpodners for years, and complained about them for at least as many years. If we have an analog backup, we won' t have to write code to simulate the poor performance (AGC capture, etc.), we can let people experience it for themselves :-)
Seriously, if we have 2 SDX's, aren't they backups for each other?
It's a concern about radiation, I think, more than anything else. Personally, I'm happy to leave it out. The SDX concept is no longer just a power point presentation and associated hand waving, it is working demo-ware, and improving with time.
Lyle