[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 14:09:58 PDT 2007


Eventually we need to deal with the radiated noise.
73,
Jim


Juan Rivera wrote:

>Chuck,
>
>I actually think that the noisy power coming out of the CAN-Do module is
>perfect for these tests.  The more I think about it the more delighted I am
>that its there.  I have no other way to generate noisy power.  This is
>great!  I'll attempt to capture this noise with my oscilloscope and post it
>in my log if I can.  My scope is not feeling well these days so I may need
>to dig up another one.
>
>Even if the receiver eventually receives its power from another source, we
>need to assume that it will have switching noise on it from other payloads.
>That's the only reasonable assumption as far as I'm concerned.  The receiver
>must be able to function in the presence of noisy power and the CAN-Do
>module is a perfect noise source.
>
>Based on the above I think I'll leave the CAN-Do module alone for now and
>see if I can add some simple filtering to kill the spurs in the IF while
>running on the switched CAN-Do power.  If it can do that then I think we
>will be on the right track.
>
>Every other payload designer should take heed and plan to operate with noise
>on their DC inputs too.  This is probably a topic that needs some high-level
>attention.  Are there any power specs that describe maximum expected noise
>levels?  Perhaps a standard DC input filer should be designed and
>incorporated in every power supply input.  Why leave this up to each
>designer?  Come up with a standard filter using SMD components.  I would
>think that this filter would also work to reduce switching noise from the
>payloads and help prevent that noise from propagating back out to other
>payloads on the power bus.  All this looks like an area that needs
>attention.
>
>I'm open to advice here.  All I was thinking of doing was adding about 10 uF
>across pins 39/40 to ground, an RF choke in series, and then another 10 uF
>cap and maybe a second smaller value to ground at the load end of that RF
>choke.  I can cobble something like that together and stick it on the PCB in
>dead bug style.  I can keep adding stages until I get rid of the noise.
>
>73,
>
>Juan
>WA6HTP
>
>-----Original Message-----
>From: Chuck Green [mailto:greencl at mindspring.com] 
>Sent: Friday, June 15, 2007 7:53 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,
>
>I have a couple of suggestions.
>
>Based on previous messages I presume you will not want to use the 
>switched power from the CAN-Do! regardless of the noise issue. I also 
>see that the switch transistor in the CAN-Do! is in the same area of the 
>PCB as the CAN-Do! power supply.
>
>1) Put a jumper between pins 2 and 3 of the switch transistor (TO-220). 
>This will bypass the switch and any noise it is picking up from the 
>power supply. This will keep the 2 amp fuse in your power source and the 
>current measurement circuit.
>
>2) You might also eliminate the 2 amp fuse from your power source by 
>placing a jumper from pins 1,9 of the DA15P to pin 2 of the switch 
>transistor after removing the transistor (or just cutting it's leads). 
>This will preserve the current measurement of the power going to your 
>module.
>
>3) You might also bypass everything by putting a jumper from pins 1,9 of 
>the DA15P to any unused user pins on that same connector (pins 
>2,3,5,10,11,12) then picking up the power from the corresponding user 
>pins on the 40 pin connector. If you do this, you should provide a 
>current measurement circuit on your module and attach it's output to one 
>of the analog input pins of the 40 pin connector.
>
>The above may eliminate or reduce the noise in your power source while 
>accomplishing other power source objectives.
>
>Chuck
>
>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_Troubleshoo
>ting.htm>.
>  
>
>>Preliminary Findings...
>>
>>1. The spurs seen in the receiver IF enter the receiver in two ways
>>
>>o As radiation from the CAN-Do inductor
>>
>>o Via CAN-Do module switched +14 VDC power on pins 39 and 40
>>
>>2. I/O line filtering appears to be unnecessary
>>
>>3. The switched power from the CAN-Do module pins 39 and 40 must be 
>>filtered
>>
>>4. The CAN-Do module will either have to be kept physically separated 
>>from any sensitive components, redesigned, shielded or a combination 
>>of the three.
>>
>>5. 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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>>Eagle at amsat.org
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>>  
>>    
>>
>
>
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>
>  
>
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