The only thing in the requirements document is the DC voltage range and that is only my estimate based on what I know about Li-Ion batteries. We need the power system designers to provide input.
73,
John KD6OZH ----- Original Message ----- From: Juan Rivera To: 'Bdale Garbee' Cc: 'David Smith' ; 'Dave Black (Work)' ; 'Dave Black (Home)' ; [email protected] ; 'Samsonoff@Mac. Com' ; 'Juan.Rivera (Work)' Sent: Sunday, June 17, 2007 17:58 UTC Subject: [eagle] Re: 70 cm Eagle Receiver - Final Spur Report (at least fortoday...)
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) 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:[email protected]] Sent: Sunday, June 17, 2007 10:04 AM To: [email protected] Cc: [email protected]; David Smith; Dave Black (Work); Dave Black (Home); Samsonoff@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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