[eagle] Re: CAN-Do Suggestions from Juan

Jim Sanford wb4gcs at amsat.org
Tue Jul 17 16:36:38 PDT 2007


Team:
I'm going to weigh in later tonight after several notes in this thread, 
but want to respond to this ASAP.

I very strongly feel that we should try our best to get the CAN-Do! 
widget to work with receivers.  I don't care if it's redesign, 
shielding, both, or whatever. 

Rationale:
In my demented mind, there are three mandatory requirements for EMI -- a 
source, a path (conducted or emitted), and a victim receptor.
We will need to work on all three, but (to a point) working on the 
source has the most bang for the buck.  I say this because, we might do 
a nice job of shielding a particular receiver, but if we ignore the 
source, we run a huge risk of unintended and unexpected/untested 
collateral effects -- like there being so much radiated noise that the 
noise floor at some antenna is unacceptable.  Reducing source 
strength.reduces total radiated noise by a factor of however many 
widgets we fly.

That said, I'm ABSOLUTELY willing to be convinced that, "We've done 
this, we've spent that, any more is diminishing returne." 

I truly feel that we should do our best to limit the source as part of 
an integrated attack on this issue. 

More later tonight.

Thanks & 73,
Jim
wb4gcs at amsat.org


Chuck Green wrote:

>Hi Juan,
>
>I agree that specifications prior to design would be helpful 
>(required?).  But as far as the EMI issues are concerned, we do seem to 
>have a chicken/egg problem.  And I'm not sure it is practical to design 
>a widget that meets the requirements of receiver modules.  Most modules 
>simply don't need anything nearly this good.  But we should do 
>everything practical to accommodate receiver modules, and maybe meet 
>their requirements completely. 
>
>Thanks,
>Chuck
>
>Juan Rivera wrote:
>  
>
>>Chuck,
>>
>>My comments might have been buried in the flurry of email a while back.
>>Things seem a bit quieter now so here they are:
>>
>>1) Don't get too far into a redesign until a top-level EMI requirement is
>>created.  This can't be done properly until prototype solar panel power
>>converters are fabricated and tested.  I would work to create a new power
>>supply with a switching frequency of at least 500 kHz while you wait
>>however.  This will make filtering much easier, the filter components will
>>be smaller, and any spurs that make it into the receiver will be outside the
>>passband of the IF.
>>
>>2) The EMI requirements for radiated and conducted emissions and
>>susceptibility should flow out of that test data and not be guesses.
>>
>>3) Once we have an EMI requirement then tradeoffs need to be considered
>>between the CAN-Do module and the enclosure - one or two compartment?  Sheet
>>metal or milled construction?  The results of that tradeoff study will
>>determine how much room you have to work with, how much front panel space,
>>and how much shielding and filtering are required.
>>
>>If I had my way the enclosure would be a two-cell milled enclosure with all
>>the RF and IF exiting out the side of the rear cell.  The CAN-Do module and
>>the Receiver switching power supply would both be located in the first cell
>>with feed-thru filtering in the common bulkhead between cells (all digital
>>power in the front and all analog in the rear).  That would mean that the
>>CAN-Do connector would be the only connector on the front of the case.  If
>>that were true then the only reason to change connectors would be to save
>>weight or increase reliability.  It would also mean that the existing CAN-Do
>>PCB footprint would be fine as it is.
>>
>>In my presentation I will suggest that the next revision of the 70 cm
>>receiver should be postponed until all of these issues are resolved.
>>
>>73,
>>
>>Juan
>>
>>
>>
>>-----Original Message-----
>>From: eagle-bounces at amsat.org [mailto:eagle-bounces at amsat.org] On Behalf Of
>>Chuck Green
>>Sent: Monday, July 16, 2007 7:47 PM
>>To: Louis McFadin
>>Cc: Dave Black ((Work)); Dave Black ((Home)); David Smith; AMSAT Eagle;
>>Samsonoff at Mac. Com; Juan.Rivera ((Work))
>>Subject: [eagle] Re: CAN-Do-Too! ??????????
>>
>>Thanks, Lou.
>>
>>I don't know of any reason not to use them either.  Obviously, it needs 
>>to meet our mounting configuration requirement so the new mechanical 
>>design can meet the objectives I stated earlier.  This means it must 
>>mount on the edge of a PCB.  I think the HD15-D has three rows of pins 
>>so I'm not sure how this can work, but I haven't looked at the various 
>>parts available so maybe this problem has been solved.
>>
>>If we are going to seriously consider using HD connectors I think we 
>>need the blessing of AMSAT's VP of Engineering and the EAGLE project 
>>coordinator.  This would be true for any change that would be pervasive 
>>in the satellite. 
>>
>>I am a little disappointed that there have not been any comments 
>>regarding the changes I saw as being made with a new design.  
>>Additions/changes/questions/etc.  I don't think we should do a new 
>>design without this discussion.  Maybe people feel these issues have 
>>been well covered in the past.  If so, a simple "looks good to me" would 
>>be helpful.
>>
>>And no one has stepped up to say they are well qualified and will design 
>>a new power supply.  Without this, I don't see a new design happening, 
>>but maybe.
>>
>>And finally, I see that no one has dared touch the subject of parts 
>>procurement I raised. 
>>
>>Obviously, most of these comments are really meant for the Cc list.
>>
>>Thanks,
>>Chuck
>>
>>Louis McFadin wrote:
>>  
>>    
>>
>>>Chuck,
>>>Mouser has a very large selection of D-sub connectors including the 
>>>high density versions. Most are in stock.
>>>I see no inherent reason for not using them.
>>>
>>>Lou McFadin
>>>W5DID
>>>w5did at mac.com <mailto:w5did at mac.com>
>>>
>>>
>>>On Jul 16, 2007, at 7:19 PM, Chuck Green wrote:
>>>
>>>    
>>>      
>>>
>>>>I have had one experience with the high density D connectors.  They 
>>>>were much larger pin count than 9 or 15!  After someone absolutely 
>>>>insisted that we use them I did the board lay out.  Turned out that 
>>>>they were *totally* unavailable!!!  I did the board layout 
>>>>again@#$%&^* using standard Sub-D's.  That was a number of years ago 
>>>>so I would hope things have changed.  If someone is absolutely 
>>>>confident they can obtain the parts we need then I'm not at all 
>>>>opposed to using them (remember, I'm not volunteering to do parts 
>>>>procurement for this project; this is a good time to use someone 
>>>>that's good at parts procurement).
>>>>
>>>>While at Goddard for P3D vib test I noticed NASA satellites using 
>>>>standard Sub-D's.  That was also a few years ago.  Anyone know of 
>>>>High Density Sub-D's being used on other satellites?
>>>>
>>>>Chuck
>>>>
>>>>Bdale Garbee wrote:
>>>>      
>>>>        
>>>>
>>>>>On Tue, 2007-07-10 at 09:02 -0700, Chuck Green wrote:
>>>>>
>>>>>  
>>>>>        
>>>>>          
>>>>>
>>>>>>The sub-miniature D connector series has served us well.  If anyone 
>>>>>>has *experience* with something they think might be a better 
>>>>>>choice, we'd love to hear about it.
>>>>>>    
>>>>>>          
>>>>>>            
>>>>>>
>>>>>At the AMSAT annual meeting that was held near Washington, D.C., a
>>>>>couple of years ago (three?), someone approached me after the CAN-Do!
>>>>>talk that Stephen and I gave to ask why we weren't using the
>>>>>higher-density connectors that put 15 pins in the same shell size as the
>>>>>9-pin version of the series we have been using... and followed up by
>>>>>sending me what looked like mil/aero-spec samples of such a part that I
>>>>>probably still have in my basement somewhere.  I'm sorry that I can't
>>>>>recall at all who that person was, but it was someone who claimed to be
>>>>>using such connectors professionally with good results.
>>>>>
>>>>>At the time, we weren't likely to be redesigning the units any time
>>>>>soon, so I didn't take any action on this suggestion.  If we're going to
>>>>>revisit the design and think we need more than 9 pins, it might be worth
>>>>>investigating higher density connectors like that?
>>>>>
>>>>>Bdale
>>>>>
>>>>>
>>>>>  
>>>>>        
>>>>>          
>>>>>
>>_______________________________________________
>>Via the Eagle mailing list courtesy of AMSAT-NA
>>Eagle at amsat.org
>>http://amsat.org/mailman/listinfo/eagle
>>
>>
>>
>>  
>>    
>>
>_______________________________________________
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>
>  
>
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