Re: [amsat-bb] SDR Prototype transponders

[Robert McGwier <rwmcgwier@xxxxxxxxxxx>]

Right.  The thing I would fight to see happen (and nothing more) is that 
we be allowed to switch into the P3E existing systems somehow and pick 
off the IF and essentially replace the analog back end with the QSD/QSE 
backend.  Again, we are using the QSD/QSE for exactly the same reasons 
Howard is using it:  very high IP3,  very good dynamic range,  
unbelievable Q, very low power.  We intendi building the EAGLE 
transponder "from the SDX out" and to allow an analog back end of less 
capability to be the "failsafe".   All we can afford to do in P3E is to 
use the existing IF's and for us to be switched in and out as any other 
back end and to make this experiment as simple and effective as it can 
be.   From what I have seen of Howard's design, there are only a couple 
of things I would change and we can discuss that as we decide who is 
doing what and what to build.  P3E project management is deciding on the 
interfaces and the specifications and the rest of us (Howard and the 
four stooges in DC, etc.) decide whether we can do it electrically, and 
in time for inclusion in the project.  This is complex.  We have to be 
controllable by the P3E control mechanisms and interface cleanly with 
the existing transponder which I believe William is doing.


Changing the bandwidth of the QSD/QSE is  . . . . .   changing 4 
capacitors.  That is all there is to it.

We (four stooges in D.C.) chose to go the "existing hardware out 
prototype".  We used two SDR-1000's and Linux software running on a 
200watt Linux computer!  We are not talking about flying a Mini-ITX 
Pentium 4 in orbit.  We are doing a demonstration of WHY one wants to do 
an SDX. Howard chose the "let me do an interface I believe will work 
with P3E" approach.  He took on the harder job of getting his DSP widget 
working before he worked on showing the software will work.   We need a 
50-100 Mhz DSP core to do this job.  So far as I know (such as Howard's 
TMS32C67) , one has not been subjected to radiation testing.   There is 
a LOT to do to get such a thing ready for P3E.  We are not fooling 
ourselves. We will collectively take the specs AMSAT-DL gives us and 
collectively decide if we can in the time alloted. 

Bob
N4HY
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