[eagle] Re: Preliminary CAN-Do EMI Findings and Suggestions to Mitigate in the 70 cm Receiver

Jim Sanford wb4gcs at amsat.org
Fri Jun 15 14:07:27 PDT 2007


Juan:
I think I concurr with our plan.
Here's how I'd like to proceed: 
    Fix the problems (microphonics, noise, passband ripple)
    Then execute the ATP.

I agree in the current condition, there's not much value in (yet) 
executing the ATP.  We are, however, getting closer.

Thanks for all your efforts and excellent documentation.

73,
Jim
wb4gcs at amsat.org


Juan Rivera wrote:

> Jim and John,
>
>  
>
> This morning I want to physically move the PCB to the back of the 
> enclosure, remount the CAN-Do module on the connector plate, and 
> connect them with a short ribbon cable.  I'll have that done in a few 
> hours and post the results in my log.
>
>  
>
> Then I'd like to try to filter the switched 13 volts from the module 
> so the receiver is spur-free and more or less configured the way I 
> think it might need to go.  Even if the receiver power bypasses the 
> CAN-Do module it looks like it needs to be able to function with dirty 
> DC power so a simple filter will probably be necessary in the next 
> revision..
>
>  
>
> Assuming that this removes the spurs from the IF output, that still 
> leaves us with passband ripple and microphonics to deal with.  I'll 
> remove the suspect capacitors that John suggests first to see what 
> affect that has on microphonics.  Then I can make John's suggested 
> modifications to try to learn more about the ripple.  The problem with 
> these changes is that it will leave the receiver in a state where 
> running the ATP might not be very useful.  I think we might want to 
> regroup after I make those changes and see what makes sense.  We might 
> want to order some film caps to replace the ceramic chips removed to 
> chase the microphonics and see what John has in mind for the ripple 
> before running the ATP.  This will push the ATP to the right by a few 
> weeks but would probably result in more meaningful test results.  What 
> do you and John think?
>
>  
>
> Juan
>
>  
>
> ------------------------------------------------------------------------
>
> *From:* Jim Sanford [mailto:wb4gcs at amsat.org]
> *Sent:* Friday, June 15, 2007 5:21 AM
> *To:* juan-rivera at sbcglobal.net
> *Cc:* eagle at amsat.org; David Smith; Dave Black (Work); Dave Black 
> (Home); Samsonoff at Mac. Com; Juan.Rivera (Work)
> *Subject:* Re: [eagle] Preliminary CAN-Do EMI Findings and Suggestions 
> to Mitigate in the 70 cm Receiver
>
>  
>
> Juan:
> As usual, good work, and well documented -- thanks!
>
> What is your plan for proceeding to execution of the ATP?
>
> After you've developed a test configuraton and executed/documented the 
> ATP,
> I'd like to see a single document, titled "Recommended changes to 
> design," which would be the single summary of all you've learned and 
> would recommend we do different in this design.  As always, I'm open 
> to a better idea.
>
> THanks & 73,
> Jim
> wb4gcs at amsat.org <mailto:wb4gcs at amsat.org>
>
>
> Juan Rivera wrote:
>
> All,
>
>  
>
> I've completed a preliminary evaluation of the CAN-Do RFI problem.  
> Please see my log for details by clicking here 
> <http://www.juanr.com/pages/hobbies/ham_radio/Eagle/CAN-Do_Noise_Troubleshooting.htm>.
>
>  
>
>  
>
> Preliminary Findings...
>
> The spurs seen in the receiver IF enter the receiver in two ways
>
> As radiation from the CAN-Do inductor
>
> Via CAN-Do module switched +14 VDC power on pins 39 and 40
>
> I/O line filtering appears to be unnecessary
>
> The switched power from the CAN-Do module pins 39 and 40 must be filtered
>
> The CAN-Do module will either have to be kept physically separated 
> from any sensitive components, redesigned, shielded or a combination 
> of the three.
>
> Moving the Can-Do module 2-1/4" forward of its normal location on the 
> receiver PCB lowers the EMI level below the noise floor.
>
> Suggestions...
>
> Create a full size PCB for the next generation receiver and shift the 
> RF components to the back of the board (away from the CAN-Do module.)
>
> Add DC input filtering to the receiver
>
> 73,
>
>  
>
> Juan
>
> WA6HTP
>
> 
>
>
>
>------------------------------------------------------------------------
>
>
> 
>
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>
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>
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>
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>
>  
>
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