grounding the dongle?

[rabbit108]

Did some antenna maintenace and afterwards had a ton of noise; noise floor looked like a roller coaster especiallly at meters. Checked everything, connectors, grounds for days without success.
Then it rained. The noise reduced significantly.

That is a classic symptom of power line noise.

Here is an example of severe electrical noise interference on VHF-High TV:

 

[rabbit108]

I live in an apartment in an assisted living facility and have an indoor antenna. The noise level is so high on VHF-Low that a TV signal has to be at least -8 dBmV (-57 dBm):



A TV signal on UHF can be as weak as -84 dBm (-35 dBmV) and still be received.

I measured the noise level on three different frequencies with my indoor antenna:

 

[krokus]

Did some antenna maintenace and afterwards had a ton of noise; noise floor looked like a roller coaster especiallly at meters. Checked everything, connectors, grounds for days without success.
Then it rained. The noise reduced significantly.

That is common with power line insulators having issues. The power company is happy to replace them, but doesn't have the time to identify which ones are failing. If you trace it down, and tell them the pole numbers, they will fix them. (There are multiple stories on this site about such things.)