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:bdale@gag.com]
Sent: Sunday, June 17, 2007 10:04 AM
To:
Cc:
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
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