[eagle] Re: 70 cm Eagle Receiver - Final Spur Report (at least for today...)

Bill Ress bill at hsmicrowave.com
Sun Jun 17 11:52:38 PDT 2007


Hi Juan.

I will add my second to that, not that I haven't already harped on this 
subject.

Along with trying to specify what the DC power to the receiver and 
transmitter modules might look like (a written down good guess based on 
past satellites would even be a place to start) - we also need to define 
what the 10MHz reference phase noise will look like. It's really tough 
committing to build LO's when you aren't certain what the reference will 
look like.

Matt Ettus asked the same question about the 10 MHz reference several 
weeks ago but I haven't seen a Eagle thread response (perhaps Matt got 
his answer off thread).

Juan Rivera wrote:
>
> Bdale,
>
> I certainly wouldn't suggest that no one in AMSAT understands power 
> distribution. I just can't find any detailed requirements. What I have 
> found was a spreadsheet (click here 
> <http://www.amsat.org/amsat-new/eagle/EaglePedia/uploads/1/14/Wiring.xls>) 
> that lays out all of Eagle’s wiring. There is no mention of shielding 
> or twisted pairs for the power. Both are important to reduce radiated 
> noise.
>
> As a newcomer I am wary of aural tradition and informal meetings as 
> good tools for development of complex systems. I think everything 
> needs to be written down in unambiguous requirements documents, 
> starting at the top level. This current exercise with the 70 cm 
> receiver is a good test of the current processes and procedures.
>
> I’ve glanced at John's new receiver specifications and I don’t see any 
> reference to input power or the EMI environment that the receiver must 
> work in. How can it be designed or tested if that environment has not 
> been specified as a requirement? It’s not John’s fault. He has nothing 
> to base it on. That’s where the top level requirements would give him 
> something to work with. Everything needs to start at the top and work 
> down. Not from the bottom up.
>
> 73,
>
> Juan
>
> -----Original Message-----
> From: Bdale Garbee [mailto:bdale at gag.com]
> Sent: Sunday, June 17, 2007 10:04 AM
> To: juan-rivera at sbcglobal.net
> Cc: eagle at amsat.org; David Smith; Dave Black (Work); Dave Black 
> (Home); Samsonoff at Mac. Com; Juan.Rivera (Work)
> Subject: Re: [eagle] 70 cm Eagle Receiver - Final Spur Report (at 
> least fortoday...)
>
> On Sun, 2007-06-17 at 08:48 -0700, Juan Rivera wrote:
>
> > I've completed my testing and analysis of the spurs that appeared in
>
> > the IF output of the 70 cm Eagle Receiver prototype. I believe I know
>
> > the source and the cause of all of them and how they can be eliminated
>
> > or rendered harmless.
>
> Nice work.
>
> Reading your report, two things strike me, neither of which I consider
>
> myself an expert on in AMSAT or elsewhere, but both of which I'll
>
> mention to help motivate the review of power system requirements you
>
> clearly hope comes next/soon.
>
> The first is that I think AMSAT does understand most if not all of the
>
> issues you're warning against regarding DC distributiong wiring. Some
>
> care was taken, for example, in planning pinouts of the 15-pin connector
>
> on the spacecraft bus side of the CAN-Do! widget, and in the proposed
>
> wiring harness design from the Black Forest meeting.
>
> The second is that I think more work is going to be required to ensure
>
> receivers behave reasonably in the presence of supply noise. For
>
> various reasons, as others have already alluded, I wouldn't count on the
>
> Eagle power bus being very quiet.
>
> Bdale, from Edinburgh
>
> ------------------------------------------------------------------------
>
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> Via the Eagle mailing list courtesy of AMSAT-NA
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>   



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