[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
> complexity of digital gates etc., in the DSP.
> Isn't P3E going with a digital IF or are they using an analog backup or
> 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
> But be aware Bruce that it's not "primarily" a software driven
> It is in fact TOTALLY software driven. There is no linear IF, just DSP
> the core. Or from another viewpoint 100,000 single point failures just
> waiting to happen.
> 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
> 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
> 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
> within a critical path which has large potential for a single failure.
> 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
> can go wrong leaving the satellite in the wrong part of the Van Allen
> 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
> 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
> 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
> option has been dropped in favour of increased trust in radiation testing
> by providing an equally vunerable duplicate DSP unit.
> Please see original question asked by Drew KO4MA with reply from W2GPS
> July 2005.
> See the Eagle specification document at
> It says "To provide a safe backup system in case of a failure in the
> 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
> analog linear driver. One or more of the receivers will also be capable
> 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
> 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
> a few months. I'll have my satellite backpack station that was used for
> 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
> 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
> include at least a bare bones analog backup transponder? Please tell me
> is the plan. Second, I'd like to encourage that software development not
> 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
> offered, with only my desire to see Eagle as succesful as possible.
> 73 and thanks for your efforts,
> Drew KO4MA
> AMSAT #33438
> Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
More information about the AMSAT-BB