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Author Topic: Identifying an RF noise source by frequency  (Read 251 times)

Weaver

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  • Retd s/w dev; A&A; 3x7km lines; Firebrick; IPv6
Identifying an RF noise source by frequency
« on: July 16, 2021, 01:39:40 AM »

I was looking at the graph of quiet line noise vs tones from my modem #4. I see the following three noise spikes, one of which I cannot identify. Anyone any clue as to what source #2 might be?
  • -132.5 dB: tone 46 * 4.3125 kHz = 198.375 kHz: 198 kHz   BBC Radio 4   Burghead   50 kW   NJ12568
  • -135.5 dB: tone 122 * 4.3125 kHz = 526.125 kHz: [??] OFCOM describes the range 505 Ė 526∑5 kHz as "MARITIME MOBILE 5.79 5.79A 5.84 / AERONAUTICAL RADIO-NAVIGATION"
  • -139 dB: tone 188 * 4.3125 kHz = 810.75 kHz: 810 kHz BBC Radio Scotland; Burghead
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Alex Atkin UK

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Re: Identifying an RF noise source by frequency
« Reply #1 on: July 16, 2021, 11:59:59 AM »

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INTAKE (ECI) 2xHome Hub 5A (OpenWRT) on Zen & Plusnet, 1xHauwei H122-373 on Three 5G Router: pfSense (i5-7200U) WiFi: nanoHD (OpenWRT) + Honor Router 3
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Weaver

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  • Retd s/w dev; A&A; 3x7km lines; Firebrick; IPv6
Re: Identifying an RF noise source by frequency
« Reply #2 on: July 16, 2021, 01:28:33 PM »

What a fool am I. Serves me right for not having done a search first. Thanks Alex.
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Alex Atkin UK

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Re: Identifying an RF noise source by frequency
« Reply #3 on: July 16, 2021, 02:07:42 PM »

If there's one flaw with the forum its the search functionality doesn't offer any options to really narrow down the results, plus its a tad on the slow side.  So while in this case a search worked quite well, I have a hard time finding my old posts sometimes.

Its a small price to pay for the quality of the content though.
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INTAKE (ECI) 2xHome Hub 5A (OpenWRT) on Zen & Plusnet, 1xHauwei H122-373 on Three 5G Router: pfSense (i5-7200U) WiFi: nanoHD (OpenWRT) + Honor Router 3
My Broadband History & Ping Quality Monitors

Weaver

  • Senior Kitizen
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  • Posts: 10068
  • Retd s/w dev; A&A; 3x7km lines; Firebrick; IPv6
Re: Identifying an RF noise source by frequency
« Reply #4 on: July 17, 2021, 06:56:27 AM »

I found a mention of a fish-finder product somewhere and now I canít for the life of me find it again. But that must have been a mistake, as this range is reserved for other uses according to OFCOM.

If #2 is a ship-shore thing, the question is "whereís the shore?". Mallaig or Stornoway are the only possibilities I can think of. Stornoway is not particularly close, but then neither is Radio 4. Mallaig seems much more likely because itís very close, but the power could be anything and easily could override the distance.

One really weird thing that I have noticed is that the spike #1 - Radio 4 - is not seen on line #1, but is seen on line #4. How can that be? Itís quite distinct, quite high, not just marginal so as to easily get buried in the noise; about 5.5dB high above the noise floor. I though to myself "better balance, better common-mode rejection" (if thatís the correct term?), but then spike #2 is seen on the other modems.
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4candles

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Re: Identifying an RF noise source by frequency
« Reply #5 on: July 17, 2021, 10:51:13 AM »

If there's one flaw with the forum its the search functionality doesn't offer any options to really narrow down the results
A Google search is often useful:

adsl "tone 122" weaver site:kitz.co.uk
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