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