Discussion point : Question 8 (EMI issue with Raspberry Pi)

Raspberry Pi is deployed in remote location which has internet access with six fab module. There is issue of USB port hub disconnecting due to EMI issues. As six fab is connected through USB port, because of this issue. Internet is disconnecting. From the kernel log buffers I came to know about this EMI issue. Raspberry pi is placed in a abs plastic enclosure IP65 and the whole setup is in completely locked pump room. Time being a crone job is running for every 10 mins to identify whether ports are disconnected or not? If ports are disconnected then crone job will reboot the raspberry

Around 3  cables are connected. 

1. Mini USB cable connected to xbee board. 
2. Micro USB cable connected to six fab (USB2.0 is used)
3. LMR 400 cable connected for extension of antenna

All the cables are procured from manufacturers and not sure of compliance

902~928 MHz we use in RF module is used in the board

The entire set up is inside a ABS plastic box

Out of 6 customer deployments, we see that there is issue with only 1 deployment. The 

How to overcome EMI issues  for raspberry pi?

Questions asked/Responses:

• Are all USB cables shielded with inductive core?
• USB ports are compliant? And what is type of USB like 2.0 or 3.0 and any cable going out or in and what type of cable also matters
• And if it's connected through cable or wire means temporary fix  you can try with ferrite clamps and clamp on that cable
• The schematics from the Raspberry Pi it is observed seen there are no EMI related protection and it is expected. If you feel having ferrite clamps is a little costly affair, try these, 
•  Try to some how insert a ferrite bead or a RC filter on data lines. 
• Does your board have a earth connection, through mounting holes? If so, check if USB connector mechanical is connected to this.. This also gives a good result.
• For using the ferrite clamp you should identify the frequency that is impacting the functionality. Do you see any source of radiation closer to the installation. Knowing the source might provide an idea on the frequency of radiation and then using a ferrite clamp which had high impedance at the frequency will help in fixing the issue.
• RF module radiation might also effect if its placed very close to the RF module because the field strength of the emission will be high
• If there any other boards apart from raspberry pi in  enclosure, proper signal grounding to be ensured.merely grounding all boards at common point might not help.
• Use cables with ferrite clamps.
• Switch off the RF module and try the test once