[eagle] Re: Receiver Spec vs. ATP, a few Suggestions and a Question or Two

Juan Rivera juan-rivera at sbcglobal.net
Sat Jul 28 17:13:22 PDT 2007


Let's consider the trade-offs...

If the CAN-Do module used a linear regulator the EMI problem (from the
CAN-Do module only) would completely disappear.  That would mean there would
probably be no need to consider a two-compartment enclosure to provide
shielding.  But the power consumption would increase.

If we were to go to the switching step-down converter I'm thinking of at 400
kHz then the EMI would be pushed out of the passband of the 70 cm Receiver.
If the PCB were laid out per the manufacturer's recommendations instead of
dead-bug as is the case now, and if the inductor was shielded, then the EMI
from the CAN-Do module should be greatly reduced.  Since I don't believe the
existing converter is operating properly this converter might actually
result in a slight reduction in power consumption.  Filtering conducted EMI
at 400 kHz will require relatively small components, saving weight.

If you go with what you have now I think you'll be flying a module with a
poorly functioning, motorboating, step-down converter and the enclosure will
need to be divided into two compartments for shielding.  You'll also need
more bulky filtering to get rid of the conducted EMI at 5 kHz.  Switching to
a shielded inductor might help the radiated EMI but that won't resolve the
problems with the poor layout of the circuit.

I know Chuck says the dead bug installation is intended to fly, but my
concern is not only for the mechanical integrity of the wiring but mostly
for the EMI implications.  Bear with me for a few days and I'll try to get
my write-up out as soon as I can.  My conclusion is that the CAN-Do module
PCB layout needs to be revised per the Maxim recommendations to get the
existing converter to stop motorboating.  If you accept that conclusion then
you might as well switch from a 5 kHz converter to one that switches at 400



-----Original Message-----
From: John B. Stephensen [mailto:kd6ozh at comcast.net] 
Sent: Saturday, July 28, 2007 4:10 PM
To: Chuck Green; juan-rivera at sbcglobal.net
Cc: 'Dave Black (Work)'; 'Dave Black (Home)'; 'David Smith';
eagle at amsat.org; 'Samsonoff at Mac. Com'; 'Juan.Rivera (Work)'
Subject: Re: [eagle] Re: Receiver Spec vs. ATP, a few Suggestions and
aQuestion or Two

Linear regulators would add 1-1.6 W of power consumption depending on 
battery voltage.



----- Original Message ----- 
From: "Chuck Green" <greencl at mindspring.com>
To: <juan-rivera at sbcglobal.net>
Cc: "'Dave Black (Work)'" <dblack at mail.arc.nasa.gov>; "'Dave Black (Home)'" 
<dblack1054 at yahoo.com>; "'David Smith'" <w6te at msn.com>; <eagle at amsat.org>; 
"'Samsonoff at Mac. Com'" <samsonoff at mac.com>; "'Juan.Rivera (Work)'" 
<Juan.Rivera at gd-ais.com>
Sent: Saturday, July 28, 2007 22:30 UTC
Subject: [eagle] Re: Receiver Spec vs. ATP, a few Suggestions and aQuestion 
or Two

> Hi Juan,
> I think the reason you have not seen much regarding the CAN-Do redesign
> is that, as far as I know, no one has stepped up to do the power supply
> redesign.  Until that happens, not much else will happen.
> I'm not thrilled with the idea of giving up the switching power supply.
> Remember that the efficiency hit must be multiplied by 10-15, the number
> of CAN-Do's on the satellite.
> The "dead-bug" modification is intended to fly.  Those who were not
> around in the early days have no idea what loose wires have flown
> successfully in the past.  That's not to say we should encourage such
> things, just that it's not as ugly to those of us who have seen much
> worse in the past as you might think.  Because of the IC's mass (very
> small) it is probably very secure just the way you see it.  But we will
> also epoxy a radiation shield to it and then conformal coat the whole
> thing with a heave conformal coating which will make it very difficult
> for anything to move.
> I'm ready to start a new design (layout) just as soon as someone gives
> us a new power supply design that is quieter, and hopefully, more
> efficient than the 90% we now have.
> Chuck
> Juan Rivera wrote:
>> Bdale,
>> It would be a trade-off.  I've put out all the information I have and
>> everyone knows my opinions.  I think someone else is supposed to be 
>> looking
>> into this but I forgot who it is since nothing has been posted.  I'd like

>> to
>> see some alternative suggestions from the experts on the CAN-Do, the
>> enclosure, and the EMI situation in general.
>> By the way, do I have a prototype CAN-Do module or was the intent to fly
>> this version with the dead-bug step-down converter hanging by three leads
>> and a few wires?
>> Juan
>> -----Original Message-----
>> From: Bdale Garbee [mailto:bdale at gag.com]
>> Sent: Saturday, July 28, 2007 2:41 PM
>> To: juan-rivera at sbcglobal.net
>> Cc: 'John B. Stephensen'; David Smith; Dave Black (Work); Dave Black 
>> (Home);
>> eagle at amsat.org; Samsonoff at Mac. Com; Juan.Rivera (Work)
>> Subject: Re: [eagle] Receiver Spec vs. ATP, a few Suggestions and 
>> aQuestion
>> or Two
>> On Fri, 2007-07-27 at 21:23 -0700, Juan Rivera wrote:
>>> I have a few thoughts...  The CAN-Do switching step-down converter is
>>> only supplying 11 milliamps.  If we take a slight efficiency hit we
>>> could just go to a simple linear regulator and completely eliminate
>>> the radiated and conducted EMI emission problem from CAN-do.  That
>>> eases the EMI filtering and shielding requirements for every single
>>> payload.  That seems like a good trade-off to me.
>> Hrm.  What makes you say "a slight efficiency hit"?
>> Doing this on one or two modules that are particularly susceptible to
>> noise *may* make sense (and I'm certainly open to considering this as an
>> alternative), but we're already on our second power supply design on the
>> CAN-Do! because the original switcher, which was more efficient than a
>> linear regulator, was deemed too inefficient to fly on P3E by our
>> AMSAT-DL friends.
>> Bdale
>> _______________________________________________
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