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

Chuck Green greencl at mindspring.com
Fri Jun 15 07:53:06 PDT 2007


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_Troubleshooting.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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