[eagle] CAN-Do Suggestions from Juan

Juan Rivera juan-rivera at sbcglobal.net
Mon Jul 16 20:34:47 PDT 2007


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.



-----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.


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 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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