All:
My OPINION, based on my experience, is that we're better off eliminating the noise at the source. 

I understand Bdale's comments about flight units being delivered already, but if it is as simple as replacing one (easily replaceable, I'm assuming) component, I think we should at least consider that option in the system level engineering decision.  I'd sure like to see the idea tested somewhere.

Again, that's my INPUT to the discussion.

Thanks & 73,
Jim
wb4gcs@amsat.org


Bdale Garbee wrote:
On Wed, 2007-06-13 at 05:06 -0700, Juan Rivera wrote:
  
Good morning Stephen,
    

I happen to be online earlier than Stephen today, due to being in
Atlanta on business, so let me provide some replies and he can chime in
later if I miss anything.

And by the way, sorry about missing the TeamSpeak meeting last night.  I
was at dinner with a number of customers in Atlanta, and then realized
the notebook I'm using now does not have a built-in microphone (and I'm
not in the habit of traveling with a headset... should probably fix
that!).

  
1)      What if the CAN-Do module suffers a failure that causes a
current overload?  Is it protected by a fuse?  The next generation
receiver should continue to function as long as it has power.  An
overload in either unit should not cause the other to fail.
    

There is no fuse on the CAN-Do! widget.  A sufficiently bad short would
probably cause a trace to cook acting as a fuse, but all of the active
circuitry is downstream of the switching regulator and thus fairly well
isolated from the spacecraft power bus in case of failure anyway.  Since
you'll be bypassing the power switch on the CAN-Do! widget anyway, I
don't think we have any significant coupled-failure scenarios.

  
2)     Do you have any information of previous efforts to reduce
CAN-Do noise by either shielding the module or replacing the inductor
with a shielded version?
    

No.  As I indicated in my email the other day, you are the first person
integrating a CAN-Do! widget with an RF payload module... at least that
we've had any feedback from.

  
3)     Do you have a shielded inductor that I could swap for the
existing one if that proved necessary?
    

No.  And frankly, solutions that involve *any* modification of the
CAN-Do! widget boards at this point are going to be problematic, since
all of the flight units have already been manufactured and functionally
tested.  That's not to say that we *can't* change the CAN-Do! widgets,
but given the relatively small number of the total that are likely to
end up in RF modules, choosing a solution that allows the CAN-Do! widget
board to be used as-is may be a better systems-level design decision.  

  
4)     Have you designed a circuit that would allow temperature to be
determined inside the receiver PCB itself, and not just on the CAN-Do
module?  This will be important, especially if the receiver is split
into two separate enclosures.
    

Not specifically, but AMSAT has significant experience with a specific
model of YSI 3-lead thermistor, and some thoughts have accumulated in
the folklore over time about other alternatives.  I'm sure Lyle or
others on-list can provide a suitable circuit example for you to use if
that becomes necessary.

  
My plan is ...
    

Sounds good.  Looking forward to hearing what you learn!

  
One last question…  How do I reduce the heartbeat timing below three
seconds?  I couldn’t find any way to do that using the net controller.
I’d like to confirm that the jump in frequency I see in the CAN-Do
module’s 5 kHz noise every three seconds goes away.
    

I'll let Stephen answer that, since I don't use Windows and thus haven't
run his recent software that I suspect you're using other than under his
direct supervision...  ;-)

Bdale