[eagle] Re: EMI Concerns

Juan Rivera juan-rivera at sbcglobal.net
Sun Jun 17 16:03:35 PDT 2007


Hello Bill,

 

I have been keeping logs on the 70 cm receiver construction and testing as
we progress from the first prototype to the first set of non-flight units.
Lot's has happened in the past few months.  You can find them all on
EaglePedia if you'd like some light reading.

 

We now have one prototype running in my shop, with a few remaining problems
to fix.  Then John is going to redesign the radio and my group will
fabricate four units.  We are getting close to that point now.  John has
released a new preliminary specification which is on Eaglepedia for review
and comments.  There is nothing in this new spec about EMI.  Based on what
I'm seeing I think this needs to be hammered out before we start ordering
parts.  I just went back and revised my last log to include a few links to
EMI surface mount filters in automotive applications.  This might be a good
place to start looking for a fix.

 

Anyway, the main issue at hand right now, in my humble opinion, is this:
The CAN-Do module, which is to be an integral part of every payload on
Eagle, and mounted INSIDE the payload chassis, ON THE PCB, produces copious
quantities of radiated and conducted noise.  I had to move the receiver PCB
2-1/4 inches away from the CAN-Do module to escape the radiated noise, and
run independent power around the CAN-Do module's normal switched +14 to
escape the conducted noise.  This is not a good thing!  I think that bad boy
needs to be quieted down somehow.

 

If you can come up with an interface control document that addresses these
issues I think that would be an excellent step in the right direction!

 

73,

 

Juan

 

  _____  

From: Bill Tynan [mailto:btynan at beecreek.net] 
Sent: Sunday, June 17, 2007 2:56 PM
To: juan-rivera at sbcglobal.net; 'Bdale Garbee'
Cc: 'David Smith'; 'Dave Black (Work)'; 'Dave Black (Home)';
eagle at amsat.org; 'Samsonoff at Mac. Com'; 'Juan.Rivera (Work)'
Subject: Re: [eagle] Re: 70 cm Eagle Receiver - Final Spur Report (at least
fortoday...)

 

Right On Juan:

 

Here is where an interface document is a nesessity. That's what I told Jim I
would undertake. But, I have been out of the Eagle loop for months and thus
didn't know that such issues were now coming up.

 

An interface document should spell out power, including power quality, not
mere pin connections and physical fit data.

 

I have a lot of catching up to do but will need a lot of help to get
started.

 

73,

 

Bill Tynan, W3XO

----- Original Message ----- 

From: Juan <mailto:juan-rivera at sbcglobal.net>  Rivera 

To: 'Bdale Garbee' <mailto:bdale at gag.com>  

Cc: 'David Smith' <mailto:w6te at msn.com>  ; 'Dave
<mailto:dblack at mail.arc.nasa.gov>  Black (Work)' ; 'Dave Black (Home)'
<mailto:dblack1054 at yahoo.com>  ; eagle at amsat.org ; 'Samsonoff at Mac.
<mailto:'Samsonoff at Mac.%20Com'>  Com' ; 'Juan.Rivera (Work)'
<mailto:Juan.Rivera at gd-ais.com>  

Sent: Sunday, June 17, 2007 12:58 PM

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
<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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