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So far I can't find any documentation on what should I do with J1 ANT GND connector on the KiWiSDR board. Am I suppose to connect it to building ground? Do I have to bond both ports on the ANT GND to Ground?
what type of antenna are you using?
grounding that point is optional IMO and may even cause an increase in the noise floor.
Ok. That's good to know. I do have increased noise issue. Maybe this is why
I either simply do not use or remove the wire&ground antenna connector on the KiwiSDR. This is because there is significant difference between the SMA and that connector's ground paths and common mode current through it can significantly raise the noise/spurious floor.
Using the 'antenna' side guarantees a return path that is through that Kiwi PCB plane and out the PS/LAN/GPS common return paths so is almost certain to make things worse as compared to a carefully connected/balanced symmetrical antenna system.
The balance as provided by baluns is nowhere near enough in most circumstances to prevent common mode currents from setting the noise floor and worsening SNR compared to that on the desired antenna. Those current sources become part of the actual antenna system no matter what one thinks the antenna is.