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

Juan Rivera juan-rivera at sbcglobal.net
Sun Jun 17 10:58:23 PDT 2007


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
<http://www.amsat.org/amsat-new/eagle/EaglePedia/uploads/1/14/Wiring.xls>
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 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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