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Chat => Chit Chat => Topic started by: Weaver on July 16, 2021, 01:39:40 AM

Title: Identifying an RF noise source by frequency
Post by: Weaver 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 – 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

Title: Re: Identifying an RF noise source by frequency
Post by: Alex Atkin UK on July 16, 2021, 11:59:59 AM

You've asked this before. https://forum.kitz.co.uk/index.php?topic=21487.0

Title: Re: Identifying an RF noise source by frequency
Post by: Weaver 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.

Title: Re: Identifying an RF noise source by frequency
Post by: Alex Atkin UK 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.

Title: Re: Identifying an RF noise source by frequency
Post by: Weaver on July 17, 2021, 06:56:27 AM

I found a mention of a fish-finder product somewhere and now I can’t 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 "where’s 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 it’s 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? It’s 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 that’s the correct term?), but then spike #2 is seen on the other modems.

Title: Re: Identifying an RF noise source by frequency
Post by: 4candles on July 17, 2021, 10:51:13 AM

Quote from: Alex Atkin UK 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

A Google search is often useful:

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