[amsat-bb] Re: The Mode B tradition
G0MRF at aol.com
Thu Sep 14 16:59:25 PDT 2006
In a message dated 9/14/2006 10:39:26 PM GMT Standard Time,
bill at hsmicrowave.com writes:
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.
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
See the Eagle specification document at
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
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 of
AMSAT LM 2232
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
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,
More information about the AMSAT-BB