All,
Please see my write-up here http://www.juanr.com/pages/hobbies/ham_radio/Eagle/CAN-Do_Noise_Troubleshoo ting.htm .
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:
1) The CAN-Do module provides dirty power - both the +13 VDC output and the ground are noisy
2) 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