[eagle] Re: Preliminary CAN-Do EMI Findings and Suggestions to Mitigate in the 70 cm Receiver
wb4gcs at amsat.org
Fri Jun 15 14:09:58 PDT 2007
Eventually we need to deal with the radiated noise.
Juan Rivera wrote:
>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
>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.
>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
>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
>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.
>Juan Rivera wrote:
>>I've completed a preliminary evaluation of the CAN-Do RFI problem.
>>Please see my log for details by clicking here
>>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
>>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.
>>. 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
>>Via the Eagle mailing list courtesy of AMSAT-NA
>>Eagle at amsat.org
>Via the Eagle mailing list courtesy of AMSAT-NA
>Eagle at amsat.org
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