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

John B. Stephensen kd6ozh at comcast.net
Mon Jun 18 13:53:31 PDT 2007

Juan and Jim:

I've been up in Davis watching my niece graduate from high-school. I looked at the blog but my brother didn't feel comfortable with me sending personal email from a government-owned PC.

It's not worth the effort to implement the entire ATP now, testing the front end is useful. The new requirements allow some specifications to be relaxed so that the SAW filters can be kept warm enough to survive eclipses. The second mixer and the circuitry between it and the output will probably change. 


  ----- Original Message ----- 
  From: Jim Sanford 
  To: juan-rivera at sbcglobal.net 
  Cc: 'David Smith' ; 'Dave Black (Work)' ; 'Dave Black (Home)' ; eagle at amsat.org ; 'Samsonoff at Mac. Com' ; 'Juan.Rivera (Work)' 
  Sent: Friday, June 15, 2007 21:07 UTC
  Subject: [eagle] Re: Preliminary CAN-Do EMI Findings and Suggestions to Mitigate in the 70 cm Receiver

  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.

  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?



    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

    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,
    wb4gcs at amsat.org

    Juan Rivera wrote: 


    I've completed a preliminary evaluation of the CAN-Do RFI problem.  Please see my log for details by clicking here.

    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.


    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






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