Sandro,
In my opinion, the way it alternates on and off I would believe it's some
type of charging device.
If you lack DF'ing equipment a small portable SW receiver is a start to
locate the noise and looking at the strength it's close to your qth. It
could be only a few hundred feet from your apartment.
A collapsing telescopic antenna would help as you get closer detune the
antenna.
The most important point here is to find it first so it can be identified
and actions can be taken to eliminate it.
Randy
WX5L
-----Original Message-----
From: RFI [mailto:rfi-bounces@contesting.com] On Behalf Of Sandro D'Onofrio
Sent: Tuesday, November 08, 2016 3:19 PM
To: rfi@contesting.com
Subject: [RFI] Nasty strong noise
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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