[eagle] Re: CAN-Do Suggestions from Juan

Chuck Green greencl at mindspring.com
Tue Jul 17 07:48:27 PDT 2007


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
>>>>
>>>>
>>>>   
>>>>         
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