[eagle] Re: CAN-Do noise abatement plan and questions

Chuck Green greencl at mindspring.com
Thu Jun 14 08:55:35 PDT 2007


Yes, the CAN-Do! s were radiation tested and did very well.  That was 
one of the first things done.  It was a special PCB that had some 
alternate parts on it for us to choose from for the final version.  The 
test was run without the Tantalum shields.  The Tantalum shields reduce 
the dose rate so we are very comfortable with the device for the 
mission.  We probably didn't need to shield everything like we did but 
it's easier to do that after testing the total device rather than try to 
figure out what each component can tolerate.  Our police is to shield 
any device that contains an FET, top and bottom.  I took this into 
consideration when designing the layout for this and the IHU so there 
are ICs of similar size on opposite sides of the PCB as much as possible 
so that the top shield on one provides bottom shielding for the other.  
It's not possible to shield the bottom of an SMD IC except to put the 
shield on the other side of the PCB anyway (J-lead SMDs are an exception 
to this but we don't use very many of them).  Tantalum does an 
outstanding job of shielding.  Sometime when I see you, ask me to tell 
you about the time I forgot I had a piece about 6" square in my 
brief-case when going through airport security.


John B. Stephensen wrote:
> Bob:
> Were they tested sufficiently for radiation resistance? I'm assuming that 
> the tantalum was used to add radiation shielding for things like flash 
> memory on the MCU. Mirek's receiver also uses flash memory to store the 
> frequency. The PLLs used in the existing 70 cm receiver can be purchased in 
> a pin-compatible rad-hard version. However, the frequency has to be stored 
> in flash memory. PIC MCUs hold data for 40 years on earth but space is a 
> harsher environment.
> We have the option of buying PLLs (with more pins) that can be hard-wired to 
> a particular frequency. These PLLs are much more expensive and have longer 
> lead times as they are space rated.
> 73,
> John
> ----- Original Message ----- 
> From: "Robert McGwier" <rwmcgwier at gmail.com>
> To: "Bill Ress" <bill at hsmicrowave.com>
> Cc: <eagle at amsat.org>
> Sent: Thursday, June 14, 2007 10:46 UTC
> Subject: [eagle] Re: CAN-Do noise abatement plan and questions
>> That they were not sufficiently tested by anyone who was to use them to
>> build flight units.  This consumed tantalum slides, and lots of effort.
>> Stephen got essentially zero feedback from the engineering test units he
>> sent.  This noise issue could have easily been found.  They have had the
>> engineering units for a LONG time.
>> Bob
>> Bill Ress wrote:
>>> Hi Bob,
>>> Just curious - what were the "objections?"
>>> Regards...Bill - N6GHz
>>> Robert McGwier wrote:
>>>> The Germans demanded their flight modules over the objections of the
>>>> designers and manufacturers so they are on their own with the
>>>> consequences.
>> -- 
>> AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL,
>> "If you're going to be crazy, you have to get paid for it or
>> else you're going to be locked up." Hunter S. Thompson
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> _______________________________________________
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> Eagle at amsat.org
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