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Re: SDR Prototype transponders



Sometimes this "hobby" makes my head hurt! hihi
;-)

Roger
WA1KAT
----- Original Message ----- 
From: "Robert McGwier" <rwmcgwier@comcast.net>
To: <amsat-bb@amsat.org>
Sent: Thursday, August 18, 2005 9:48 AM
Subject: Re: [amsat-bb] SDR Prototype transponders


> 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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