CAN-Do guys,
Can someone
supply me with a suitable shielded replacement for the L3 inductor? I’ll
be happy to swap it out and report back.
Juan
From: Jim Sanford [mailto:wb4gcs@amsat.org]
Sent: Sunday, June 17, 2007 7:35
PM
To:
Cc: 'Chuck Green'; 'David Smith';
'Dave Black (Work)'; 'Dave Black (Home)'; eagle@amsat.org; 'Samsonoff@Mac.
Com'; 'Juan.Rivera (Work)'
Subject: Re: [eagle] Re: 70 cm
Receiver IF Spurs - Problem Solved
Team:
I ABSOLUTELY agree with Juan's assertion that
... it needs to be free of radiated and conducted
EMI in both directions.
We need to resolve these issues, and then issue such resolution as a
requirement.
Size of incoming power conductor is a spacecraft issue, that we need to get
into the Black
Eliminating the radiated noise is a CAN-Do! issue and should be solved --
especially if it is as simple as replacing a radiating inductor with a shielded
inductor.
In my professional life, I've seen a similar situation, where such an inductor
in a VERY sensitive instrumentation system was picking up noise, a fatal
flaw. Replacing the one component with a shielded equivalent solved the
problem.
We should at least TRY such an approach. .. .
Juan, I'd like you to do the swap and then give us before and after plots and
analysis. That will conclusively prove or disprove the issue.
Thanks & 73,
Jim
wb4gcs@amsat.org
Juan Rivera wrote:
At least in this particular case jumpering across the
switch didn’t work. (See my log for today on Eaglepedia.)
Since the CAN-Do module is such an imbedded and
pervasive component in Eagle, I think it needs to be free of radiated and
conducted EMI in both directions. It's a great little interface but I'm
afraid it has some very serious shortcomings at the moment:
Conducts noise
back towards the power source where it can impact other loads on the same power
bus (one ohm of resistance out there was enough to screw up the receiver.)
Provides a noisy
+14 to its load (the noise went right through the receiver like fat through a
goose and ended up in the IF as spurs.)
Radiates EMI that
can adversely affect sensitive circuitry at a distance of over two inches from
the rear of the PCB
Attempting to mitigate those problems will put a huge
burden on every payload and the adverse impact might not be fully known until
integration and test, if then. Trying to go back and band-aid something
like this after all the payloads come together would be a very bad corner to
get backed into. You could do what I did and sacrifice 2 inches of space
inside every module chassis, or you could try to build a two-section chassis
and filter the lines passing through the bulkhead, adding complexity. But
that doesn’t address the potential impact to another payload from the
spikes that are propagated back towards the common +14 bus.
I would expect that every receiver, block up or down
converter, transmitter, or amplifier will be impacted by this noise in a similar
way. In my opinion this is a global problem that needs a global
solution. If the CAN-Do module can be made EMI-free, or meet a yet to be
determined EMI spec, then all of the payloads teams can start their design with
a known environment.
If the CAN-Do module is not modified then I think the
only safe thing to do is to build each payload so it can function using CAN-Do
switched +14 volt power (the receiver can’t in the Rev-A
configuration.) If your payload can function with that noisy +14, without
any adverse impact, then it is probably a pretty well protected circuit and
should be fairly immune to whatever noise is added to the source by conducted
EMI from other loads on the power bus. It just seems simpler and cleaner
to fix the problem at the source.
I have an idea for a noise generator that I will stick
on my log... This could be the go/no go test for each payload.
I’ll go sketch it up and get it uploaded by about 2000 Pacific Time.
73,
Juan
-----Original Message-----
From: Chuck Green [mailto:greencl@mindspring.com]
Sent: Sunday, June 17, 2007 5:51 PM
To:
Cc: eagle@amsat.org; Bill Ress; Dave Black
(Home); Dave Black (Work); Dave hartzell; David Smith;
Subject: Re: [eagle] 70 cm Receiver IF Spurs - Problem Solved
Hi Juan,
One of the purposes of the CAN-Do! was to provide a
standard interface
so that a module couldn't do something nasty and take
out the entire
satellite. So custom mods to the CAN-Do! are not
allowed. Having said
that, we have always assumed that a jumper across the
CAN-Do! power
switch would be installed for those modules that
needed to be powered up
no-matter-what.
Chuck
Juan Rivera wrote:
> Chuck,
>
> I don't want to tear into the CAN-Do
module. I feel like it is a loaner and
> not mine to modify. It would be interesting
to disconnect the switch and
> the current monitor from the CAN-Do power input
and move it to those user
> pins as you suggest. That might just work,
but I also know they don't want
> to have multiple versions of the module floating
around and this would be
> one.
>
> We also can't loose sight of the radiated noise
from that inductor. I can
> see signs of EMI if it gets within 2 inches of
the sensitive areas of the
> receiver.
>
> 73,
>
> Juan
>
>
> 73,
>
> Juan
>
> -----Original Message-----
> From: Chuck Green [mailto:greencl@mindspring.com]
> Sent: Sunday, June 17, 2007 9:18 AM
> To:
> Subject: Re: [eagle] 70 cm Receiver IF Spurs -
Problem Solved
>
> Hi Juan,
>
> I am impressed with your testing and analysis.
>
> I find it curious that you were unable to filter
the power from the
> CAN-Do! . But switching noise is notorious
for being difficult to
> filter. So maybe that is something to just
forget. But in a total
> system (satellite) it may not be possible to
forget. We may need to
> find a way to filter the power for sensitive
modules even if not using
> power from the CAN-Do! ; in which case, such a
filter may also filter
> the noise from the CAN-Do! .
>
> If your analysis is correct, and it certainly
seems to be, then it would
> also seem possible to remove the switch from the
CAN-Do! (not just
> bypass it) and rout your clean power source
through the CAN-Do! current
> measurement circuit thus saving having to do this
in the module.
>
> Great work! And thanks.
>
> Chuck
>
>
>
> Juan Rivera wrote:
>
>> Hi Chuck,
>>
>> Bad news I'm afraid. See my report for
details... I've sent out a link
>>
> to
>
>> the group.
>>
>> 73,
>>
>> Juan
>>
>> -----Original Message-----
>> From: Chuck Green [mailto:greencl@mindspring.com]
>> Sent: Saturday, June 16, 2007 8:57 AM
>> To:
>> Cc: eagle@amsat.org;
David Smith; Dave Black (Work); Dave Black (Home);
>> Samsonoff@Mac. Com; Juan.Rivera (Work)
>> Subject: Re: [eagle] 70 cm Receiver IF Spurs
- Problem Solved
>>
>> Hi Juan,
>>
>> This is fantastic!
>>
>> Please try one more experiment. Pass
the module current through the
>> current measuring circuit on the CAN-Do!
while bypassing the switch
>> transistor (you could just short across the
switch transistor) and see
>> if the problem reappears.
>>
>> If you end up having to use the user pins,
you will need to add current
>> measuring circuitry to your module.
While this is no big deal, its one
>> more thing you might not have to do.
>>
>> Chuck
>>
>> Juan Rivera wrote:
>>
>>
>>> All,
>>>
>>>
>>>
>>> The 70 cm Receiver spur problem has been
solved. Click here
>>>
>>>
>>>
> <http://www.juanr.com/pages/hobbies/ham_radio/Eagle/CAN-Do_Noise_Troubleshoo
>
>> ting.htm>
>>
>>
>>> for details.
>>>
>>>
>>>
>>> 73,
>>>
>>>
>>>
>>> Juan
>>>
>>> WA6HTP
>>>
>>> ------------------------------------------------------------------------
>>>
>>>
_______________________________________________
>>> Via the Eagle mailing list courtesy of
AMSAT-NA
>>> Eagle@amsat.org
>>> http://amsat.org/mailman/listinfo/eagle
>>>
>>>
>>>
>>
>>
>>
>
>
>
>
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