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Electronics => Beginners => Topic started by: rfguy2020 on October 31, 2024, 12:43:19 pm

Title: Metal enclosure grounding
Post by: rfguy2020 on October 31, 2024, 12:43:19 pm
Hi,

I have problem similar to this: https://electronics.stackexchange.com/questions/455276/shielding-and-ground-loops-rf-panel-jacks-for-gps

I'm designing PCB and I would like to connect heat sink to the case and then I have some coaxial RF connectors (operating frequency 600MHz - 1300MHz). Then I have some IO/ethernet/USB/Power connectors. I have metal enclosure.

I'm concerned about EMC issues. According to my understanding, the best practice would be connect connector shields and mounting screws through 1Mohm resistor in parallel with capacitor to signal ground. There was some suggestions to use isolated coaxial connectors, but I still have my heatsink connected to signal ground and chassis ground. I have not seen isolated coaxial connector used in many products. I'm not sure if isolated coaxial connector is actually causing more EMC problems.

Would it be the best option to connect heatsink, coaxial connector and other connector shields to signal ground as low impedance as possible?

Or should I try to have high DC impedance between signal ground and chassis ground (through resistor parallel with cap)? I guess it might be possible if heatsink is anodized and I would use isolated coaxial connectors.
Title: Re: Metal enclosure grounding
Post by: selcuk on October 31, 2024, 01:40:36 pm
Usually a low impedance ground connection is better for EMC purposes. You may read the message and the document in the link to see the difference between direct connection and using parallel components. This information is not specific to RF connectors by the way.

https://www.eevblog.com/forum/projects/why-usb-c-gnd-is-being-connected-to-the-shield-of-the-cable-after-connecting/msg5269563/#msg5269563 (https://www.eevblog.com/forum/projects/why-usb-c-gnd-is-being-connected-to-the-shield-of-the-cable-after-connecting/msg5269563/#msg5269563)
Title: Re: Metal enclosure grounding
Post by: Terry Bites on November 01, 2024, 01:49:48 pm
Your RF io is low impedance, say 50R?
In that case (no pun intended) do ground loops really matter?
Is this a concern or an observed problem.
An isolated connector allows you to float the input/ output. Why would you do that. All RF grounds need to be tied together with a low impedance path.
If they don’t then there's a high chance that the grounds will either be susceptible to or create RFI.