The noise level on my doublet has steadily increased and is now over S9 on the lower bands. I have been looking into what I can do about it and have got to the point where I can experiment.
I am blessed with a long garden, 50 metres long and 9 metres wide, with high trees at the far end. Beyond my boundary is the car park for a club before the rear gardens of the next row of houses. I reasoned that if I moved the antenna to the lower end of the garden and used coax with a choke each end I would minimise the noise from my row of houses and would be too far from the next row to have much trouble with them. I purchased a 20 metre long wire antenna terminating in a 9:1 unun and ran it from the mid point of the garden to the trees at the far end. Since it was a proof of concept exercise I used cheap flexible coax that I had to hand, winding nine turns on a toroid near the unun and nine turns on a toroid adjacent to the ATU. This is a long run of coax, about 50 metres, so the losses are bound to be significant.
The result from the new antenna was remarkable. On 20 metres the noise fell from S8 to about S1, and the band was full of stations that had been hidden by noise earlier in the day! There were a few S points of noise on 80, 60 and 40 but I could cope with it - I had my ham radio back and was jubilant. The one fly in the ointment was that at 18:00 local time a severe noise source started up and continued until 01:30 before vanishing. This appears to come from the club building adjacent to the far end of the antenna, but I will need to confirm that before taking any action.
The next step is to replace the long run of cheap coax with something much less lossy, though I doubt that my toroidal chokes will be possible with better coax! In the future I may try an 80 metre OCF dipole, it may be noisier as the near end will be closer to the house but it will be more efficient on the lower bands.