[eagle] Re: 70 cm Receiver Spur Source Found

[John B. Stephensen]

The ripple problem is not resolved, but is likely to be in concert with reducing power dissipation in adjacent components. The SAW filters need to be kept warm (-35 C) during eclipses so the second mixer needs to be replaced with something that dissipates less power. This will raise the input impedance and make the matching circuitry less critical.

73,

John
KD6OZH
  ----- Original Message ----- 
  From: Jim Sanford 
  To: juan-rivera at sbcglobal.net 
  Cc: eagle at amsat.org ; Bdale Garbee ; Bill Ress ; Dave Black (Home) ; Dave Black (Work) ; Dave hartzell ; David Smith ; Dick Jannson ; Don Ferguson ; John B. Stephensen ; Juan.Rivera (Work) ; Lyle Johnson ; Phil Karn ; Robert Davis KF4KSS ; Robert McGwier ; Samsonoff at Mac. Com ; Stephen Moraco ; 'Steven Bible' ; 'William A Schmitt' 
  Sent: Monday, June 11, 2007 00:44 UTC
  Subject: Re: 70 cm Receiver Spur Source Found


  Juan:
  Can you "sniff" the various lines from CAN-Do! to get an idea of which is the source?

  Also, my memory is that we still have an open issue with the passband ripple -- or did that get resolved and I missed it?

  Again, thanks for all you're doing.

  73,
  Jim
  wb4gcs at amsat.org


  Juan Rivera wrote:

    All,



    The source of the spurs in the 70 cm prototype receiver is the CAN-Do module.





    This is the receiver IF output as designed

    (powered from pins 39 and 40 of the CAN-Do Module)







    This is the receiver running off of a separate power source

    (bypassing the CAN-Do Module +13 volt output on pins 39 and 40)







    This is the same configuration as above, but with the CAN-Do module shut down



    From the above it appears that:



    <!--[if !supportLists]-->1.    <!--[endif]-->The CAN-Do module is the source of all the spurs that I see

    <!--[if !supportLists]-->2.    <!--[endif]-->None of the spurs are being generated by the receiver's internal power supplies

    <!--[if !supportLists]-->3.    <!--[endif]-->Some, but not all, of the noise is entering the receiver via the switched +13 volt CAN-Do output on pins 39 and 40

    <!--[if !supportLists]-->4.    <!--[endif]-->The remainder of the noise could be entering the receiver on other CAN-Do pins, or being radiated to receiver components or traces in close proximity



    See my log for all the intermediate steps I took to reach these conclusions.



    Remaining RF issues:



    <!--[if !supportLists]-->1.    <!--[endif]-->Phase noise

    <!--[if !supportLists]-->2.    <!--[endif]-->Microphonics



    73,



    Juan

    WA6HTP
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