[eagle] Re: CAN-Do noise problem is proving to be a difficult one to fix

Jim Sanford wb4gcs at amsat.org
Fri Jun 15 15:48:24 PDT 2007


Juan:
Bob Davis et al are considering the milled approach, so I don't think 
you need to spend much more effort on that. 

I think the best use of your time and talent is to continue getting the 
receiver to work perfectly and then test it, and then document what 
works.  That will be translated into requirements which will be fed into 
whatever areas (structure, power) are necessary.

When you get a chance to search out history, if you go look at the 
results of the "Black Forest meeting" in 2005, you'll see a NOTIONAL 
power and buss concept.

Thanks & 73,
Jim
wb4gcs at amsat.org


Juan Rivera wrote:

> Jim,
>
>  
>
> I'll need the CAN-Do folks to come up with a shielded inductor that 
> will have the same form, fit, and function.
>
>  
>
> I know John has been working on a two-chassis implementation for the 
> receiver to try to get around the thermal issues that have been 
> raised, but I am personally apprehensive due to the added complexity 
> of any interconnects that will be required.  I don't want to beat this 
> milled chassis idea to death but it might be worth considering from a 
> thermal standpoint.  If you had enough thermal mass in the chassis 
> perhaps it would never have time to reach those extreme low 
> temperatures during an eclipse, rendering the need for a two-chassis 
> approach unnecessary.  It would eliminate my concern about flexing and 
> with a milled enclosure you could also move the noisy CAN-Do module 
> into a separate compartment and filter the power through the common wall.
>
>  
>
> I've been thinking about DC power distribution in general.  Can 
> someone explain the plan for Eagle to me?  In aircraft, at least in 
> the one I am familiar with, they do not use the chassis as a return.  
> All DC power is treated the same way as AC power and distributed from 
> a common point as a twisted pair to minimize common mode noise.  Great 
> care is taken to eliminate ground loops by insuring that the ground 
> returns are back through the twisted pair to the source and not 
> through a sneak path to the frame.
>
>  
>
> Juan
>
>  
>
> ------------------------------------------------------------------------
>
> *From:* Jim Sanford [mailto:wb4gcs at amsat.org]
> *Sent:* Friday, June 15, 2007 2:16 PM
> *To:* juan-rivera at sbcglobal.net
> *Cc:* eagle at amsat.org; eagle at projectoscar.net
> *Subject:* Re: [eagle] CAN-Do noise problem is proving to be a 
> difficult one to fix
>
>  
>
> Juan:
> My thoughts:
> 1.  We must stop the radiated noise.  Let's try obtaining and placing 
> a shielded inductor on the CAN-Do! module.
> 2.  I just read a great suggestion from Lou, amplified by a phone call 
> I just had with Rick, regarding three terminal filter devices.  Seems 
> like a good start.
> 3.  I agree that we need to review the bidding on packaging.  That 
> will probably be the LAST of these issues we take on.
>
> Thanks & 73,
> Jim
> wb4gcs at amsat.org <mailto:wb4gcs at amsat.org>
>
>
> Juan Rivera wrote:
>
> All,
>
>  
>
> Please see my write-up here 
> <http://www.juanr.com/pages/hobbies/ham_radio/Eagle/CAN-Do_Noise_Troubleshooting.htm>.
>
>  
>
> The CAN-Do noise is not lending itself to an easy cure.  I think this 
> whole subject of RFI/EMI needs to be looked at closely.  Every payload 
> will be affected by noise on its inputs and can affect other payloads 
> by creating noise that is propagated back out from within its module 
> chassis.
>
>  
>
> With the current scheme, of having a CAN-Do module located in the same 
> case as the main payload, there are several issues that need immediate 
> attention:
>
>  
>
> The CAN-Do module provides dirty power - both the +13 VDC output and 
> the ground are noisy
>
> The CAN-Do's switching power supply inductor, L3, radiates noise that 
> can affect sensitive circuits several inches away.
>
>  
>
> Both of these factors are adversely impacting the 70 cm breadboard 
> receiver in the form of 5 kHz spurs on the IF output.  As I mentions 
> earlier, Rather than work to clean up the CAN-Do module immediately, 
> we should focus on making the receiver function In the presence of 
> this noise.  This approach will result in a more robust design.  The 
> CAN-Do module needs to be cleaned up, but for now it acts as a great 
> real-world noise generator.
>
>  
>
> I'm currently out of ideas.  I'd like to hear what you all have to say.
>
>  
>
> 73,
>
>  
>
> Juan
>
> WA6HTP
>
> 
>
>
>
>------------------------------------------------------------------------
>
>
> 
>
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>
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>
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>
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>
>  
>
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