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

John B. Stephensen kd6ozh at comcast.net
Mon Jun 18 14:10:45 PDT 2007


A 4-terminal filter may be best. There should be no ground return path for the noise other than through the chassis. In a previous email someone stated that AMSAT had little success with capacitor-input filters. This would be because noise currents flow through the input inductor and create a differential accross the ground return lead. RF chokes using high-permiability ferrite should block noise currents in the DC power input to the receiver PCB. The easiest way to try this is to wind the power leads around a ferrite core. 

73,

John
KD6OZH
  ----- Original Message ----- 
  From: Jim Sanford 
  To: juan-rivera at sbcglobal.net 
  Cc: eagle at projectoscar.net ; eagle at amsat.org 
  Sent: Friday, June 15, 2007 21:16 UTC
  Subject: [eagle] Re: 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


  Juan Rivera wrote: 
    All,



    Please see my write-up here.



    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:



    <!--[if !supportLists]-->1)    <!--[endif]-->The CAN-Do module provides dirty power - both the +13 VDC output and the ground are noisy

    <!--[if !supportLists]-->2)    <!--[endif]-->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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