[RFI] Nasty strong noise

Sandro D'Onofrio sandro at i7ale.com
Tue Nov 8 16:19:06 EST 2016


Good morning to all, and thank you for your attention. 

Me too, I have my share of RFI inconvenience!



Since when I moved into this apartment in town, about three years ago, I am plagued by a nasty noise.  



The noise is present on the whole HF band and below: checked from 470 KHz to 29 MHz



It is strongest on the 80m band (s 9 +) and gradually decreasing. On 7 MHz it is S 9, on 10 MHz S 7-8, on 14 MHz S 7, and so on. On 1.8 MHz it is S 6-7.



There are broad  peaks, and more evident notches, about every 14 KHz. On a S9 signal the  notches are S 7. 

When it starts it sounds like a motor starting from stopped but quickly accelerating to the "work" speed. Also the sound when coming to a halt is quite particular.

The noise (on 80m) sounds like a hammer drill struggling to drill a hole in a concrete wall.  This "drill" noise is more evident in places again about 14 KHz apart.



On the rest of the frequencies it sounds like a strong hiss, or as the noise (on the radio) of a nearby electric motor.



The noise is not continuous. It comes in bursts, lasting from a few seconds to one minute, sometimes more. The "no noise" periods between the bursts are also variable, from a few seconds to several minutes.

The table below shows an example of its timing pattern, no difference if day or night, work days or weekend.

      -          duration of burst
     30"
     32"
     24"
     36"
     28"
     18"
     
      -          time from end of burst to start of next one
     11"
     8' 12"
     1' 46"
     15"
     1' 11"
     10"
     


          42"
     42"
     43"
     41"
     41"
     43"
     13"
     31"
     
     
       1' 11"
     3' 17"
     14"
     30"
     2' 13"
     15"
     12"
      
     
                   



You can listen to it on youtube:   https://www.youtube.com/watch?v=CtNehVAidCg&list=UU_3tukKeDF4oKhfAzqqRKXA

(my channel, 4 short video)



It does not originate in my apartment: listening with a battery radio on 7 MHz I switched the house main power off, and the noise was still there. (there are no UPS in the house).

When disconnecting the antenna the noise is much weaker (so it should not be coming via the power lines)



Any suggestion will be highly appreciated!



Sandro, i7ALE


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