Great changes in noise level with change of antenna!
I was on 80m band with my new half wave dipole antenna. Changed over to multi-band fan dipole to move on to 40m band. Meanwhile I had forgotten to change the band in the radio. It was then that I noticed the striking difference in the noise level on the signal strength meter (S meter)! This is the clip with 80m dipole antenna, showing high level of noise. Audio has been muted, just concentrate on the S meter for this and subsequent clips. Audio levels will also be controlled by automatic gain control and hence an unreliable indicator. You can see the S meter needle above S9 level.
See what happened when I changed over to the multi-band fan dipole antenna with elements for 40, 20 and 10m. There is hardly any noise seen on the S meter. Reason may be that this antenna is not resonant for 80m band. The apex of this antenna is at 10m while that of the 80m antenna is only at 5.5m.
Comparing noise level on different bands
Intrigued by such a gross difference, I checked 40m band with the fan dipole. It shows nearly S8 noise level. That means signals below that level will be drowned in the noise and I will not be able to hear. The antenna used just 15m RG213 coax and a 1:1 current balun at the feedpoint.
Noise was S9+ on 20m band. I did all these tests at around 6.30 am. It may worsen as day progresses and more devices in the neighbourhood become active, including solar panels.
When I checked 15m band, the noise was S6-7. But the band is most likely closed at that time in the morning.
Lower noise on CW mode
I came back and checked noise level on 40m after choosing CW-L mode. Interestingly, noise level is only S2-3. CW-L mode with filters has reduced the noise pickup. Please note that I have not enabled noise blanker or digital noise reduction. That will show up in the display as NB and DNR. I had video clips of 10m band as well. But I had forgotten to disable these filters and hence discarded those clips to avoid bias in the comparison.
Saw the same pattern of lower noise of S2-3 on 15m as well, on CW-U mode. From these observations, I feel that resonant antenna can pick up more noise than an antenna which is not resonant for that band. Of course, resonant antenna will pick up the stations also better. Filters in CW mode reduce noise level significantly.