[amsat-bb] Re: The Mode B tradition

John B. Stephensen kd6ozh at comcast.net
Thu Sep 14 18:22:22 PDT 2006

The Eagle design criteria doesn't permit single-point failures in the 
analog-mode transponder. Hardware is designed to eliminate that possibility. 
If the idea is that the signal-processing software has 100,000 instructions 
in it so each could fail, it doesn't work that way. Software is tested to 
elimiate potential failure paths. A software-defined transponder has already 
been demonstrated at the Dayton Hamvention with real users.



----- Original Message ----- 
From: <G0MRF at aol.com>
To: <bill at hsmicrowave.com>; <brobertson at mta.ca>; <amsat-bb at amsat.org>
Sent: Thursday, September 14, 2006 23:59 UTC
Subject: [amsat-bb] Re: The Mode B tradition

> In a message dated 9/14/2006 10:39:26 PM GMT Standard Time,
> bill at hsmicrowave.com writes:
> Hi  David,
> Help me out with the 100,000 single point failures. Are you  referring to 
> the
> complexity of digital gates etc., in the DSP.
> Isn't  P3E going with a digital IF or are they using an analog backup or 
> vice
> versa? That's the SDX thingy isn't it?
> Regards...Bill -  N6GHz
> Hello Bruce / Dom.
> I agree, the UV on Eagle will be  apparently analog (ue) to the casual 
> user.
> But be aware Bruce  that it's not "primarily" a software driven 
> transponder.
> It is in  fact TOTALLY software driven.  There is no linear IF, just  DSP 
> in
> the core.  Or from another viewpoint  100,000 single  point  failures just
> waiting to happen.
> 73
> David   G0MRF
> Hello Bill.
> As I understand it, and perhaps I'm being a little over conservative in my
> concern, The Eagle design has shifted with respect to the caution  of
> engineering that was shown just 14 months ago.
> My reference to 100,000 single point failures just waiting to happen was
> aimed at the UV SDX transponders total reliance on some very impressive 
> but
> completely untried in space digital electronics. From the various messages 
> on  the
> BB in the past 2 weeks I understand that the line up of the transponder 
> is:
> U band receiver to 10.7MHz - DSP based core processing the signal at
> baseband - Then an upconversion process that goes to 10.7MHz then 145MHz.
> This would appear to place the DSP it's software and its control 
> electronics
> within a critical path which has large potential for  a single failure. 
> For
> example if one of the junctions in the DSP is 'hit',  then the transponder
> stops working.  - There is no plan B.
> OK, Yes it will be radiation tested, but as I pointed out in a previous
> mail, it will be launched at the peak of the sunspot cycle and orbital 
> manouvers
> can go wrong leaving the satellite in the wrong part of the Van Allen 
> belts.
> Let's look at our own history: AO-10 was placed in a high radiation
> environment and within a short period the IHU died. However, the RF 
> components  in the
> transponder continued to function and the satellite provided a limited
> service.  Why did it continue to function? Well, I can only guess. But how 
> about
> the possibility that RF devices with large junctions are less vunerable to
> radiation than sub 1 micron devices in LSI logic. In AO-7, the RF 
> components are
> still working 20 years on.
> I have suggested that a simple signal path be designed around the SDX 
> core.
> Signals appear to exist at 10.7MHz and adding just a few extra components
> would  allow a malfunctioning SDX to be bypassed.
> What is really curious is that these fears have been voiced before and
> reassurances were given by Rick W2GPS.
> However for some reason, what seems to be a prudent, inexpensive and 
> simple
> option has been dropped in favour of increased trust in radiation testing 
> or
> by  providing an equally vunerable duplicate DSP unit.
> Please see original question asked by Drew KO4MA with reply from W2GPS 
> dated
> July 2005.
> ==============================================================
> Drew,
> See the Eagle specification document at
> _http://www.amsat.org/amsat-new/eagle/Eagle_Fall_2004.php_
> (http://www.amsat.org/amsat-new/eagle/Eagle_Fall_2004.php)
> It says "To provide a safe backup system in case of a failure in the 
> digital
> implementation of the linear transponders there will be two S-Band
> transmitters and
> either of them will be capable of being driven by the SDR  driver or by a
> traditional
> analog linear driver. One or more of the receivers  will also be capable 
> of
> analog
> operation."
> Rick
> AMSAT LM  2232
> -----Original Message-----
> From: owner-Eagle at AMSAT.Org [_mailto:owner-Eagle at AMSAT.Org_
> (mailto:owner-Eagle at AMSAT.Org) ] On Behalf  Of Andrew
> Glasbrenner
> Sent: Sunday, July 24, 2005 7:45 PM
> To: Robert  McGwier; Amsat-Bb
> Cc: Jim Sanford
> Subject: [eagle] Re: [amsat-bb] LONG and  long overdue report
> Hi Bob,
> Thank you very much for the update on  the Eagle transponder progress. The
> SDR based transponders sound very  cutting edge and extremely adaptible to
> AMSAT's needs. I very much look  forward to hearing them at the symposium 
> in
> a few months. I'll have my  satellite backpack station that was used for 
> the
> Dayton demos, and will be  glad to offer it up for demonstrating the new
> transponders. CC Rider is also  very exciting and sure to open new realms 
> of
> small stations and portable  operation.
> As someone primarily looking in from a user/member point of  view I would
> like to offer two comments. First, I'd hate to think we are  going to hang
> our entire mission on just the SDR transponders. Wouldn't it  be prudent 
> to
> include at least a bare bones analog backup transponder?  Please tell me 
> this
> is the plan. Second, I'd like to encourage that software  development not 
> lag
> too far behind the hardware. I'm not a big fan of the  idea of writing the
> code once it's in orbit. One does not have to look too  far to find where
> AMSAT has oversold or overpromised features based on  writing the software
> after launch. Please take these comments in the spirit  with which they 
> were
> offered, with only my desire to see Eagle as succesful  as possible.
> 73 and thanks for your efforts,
> Drew KO4MA
> AMSAT  #33438
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