Hello Howard!
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.
As we won't now have an opportunity to discuss this in a telecon, can we have a clear line on this? I can just see that someone's gonna ask me this question at my presentation.
One configuration we discussed at one time was to put an "analog IF" inside the SDX. With the SDX operating with a nominal 10.7 MHz IF, we'd simply switch in a gain section with AGC, or switch it out and switch in the digital processing system. That way, the SDX device would contain both analog and digital transponder circuitry, under control of the CAN bus, and with little added mass or complexity.
The power-on default mode would be analog so in case of an AO-10-liek state, we'd have the highest probability of something working, even if it wouldn't be optimal.
73,
Lyle kK7P