[amsat-bb] Re: The Mode B tradition

[G0MRF@aol.com]

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
W2GPS
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