The Noise Is Back In Town!

Noise and interference issues?
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John Faulkner, Skegness
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The Noise Is Back In Town!

Post by John Faulkner, Skegness » 27 Jan 2015 17:22

As sung by Thin Lizzy back in the 70s no less! Not to be confused with Sabrina's "Noise Noise Noise", Don Henley's "The Noise Of Summer" (now appearing during the winter months too!) and Wham's "Bad Noise".

Humour(?) over. For the last few days Medium wave has largely been demolished by a rough sounding 50 Hz growling, sounding exactly like the old analogue TV interference we all used to know and love. The noise tapers off to some degree by 15 to 20 MHz, but only because the flag antenna doesn't go up any higher. This noise is also affecting chunks of band 2, but leaving the rest of the band 'dirty' sounding. This noise is plainly visible in the FDM-S2's waterfall. Thankfully, at the moment, it isn't present all the time. I will try and track this down in the days ahead.

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John Faulkner, Skegness
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Re: The Noise Is Back In Town!

Post by John Faulkner, Skegness » 28 Jan 2015 11:07

https://app.box.com/s/q5tablixi03fdc5kuoaj4merhydhoki0

Just grabbed a recording of this. The noise if affecting frequencies between 97.6 and 99.0 at the moment. The Living Joy song you hear is Radio Decibel on 97.6. The next music you hear is BBC Radio 1 on 98.3 so this should give you an idea of the extent of the problem. Luckily, this noise is not there all the time but looks like being a daytime thing at the moment. I won't be making any complaints to Ofcom due to the limited freqencies affected, not that I would expect them to do anything if I did! There's a bit of general mushiness on other parts of the band which may or may not be tied in with this but, overall, things are not as bad as they might be. It's no big deal and my aerial is still lowered so I hope that raising it soon will help matters. Medium wave remains a wash-out for the top half of the band when this noise is present.

Next to take a portable outside to see if I can track this down.

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John Faulkner, Skegness
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Re: The Noise Is Back In Town!

Post by John Faulkner, Skegness » 16 Feb 2015 17:40

Bring on MORE noise! Why not? Yesterday and today I see a new noise, although it looks like it's an extension of the random and brief (lasting a few seconds) noise bursts I get anyway. The appearance is the same.

Since early yesterday evening I have an almost total wipeout of the band. It's a rough white noise with a lot of growling 50Hz mush. It varies in strength, but even when it's not at its worst it can be heard at equal levels with Belmont, so you can imagine the devastation it causes across the rest of the band. Lille and Egem are just buried, as was the majority of meteor scatter overnight. Occasionally I see bursts of pure white which smothers everything across the band

Occasionally, either end of the band clears, though not totally. The bottom of the band can open up slightly, together with a few frequencies around 99 MHz. but the overall damage to the band renders me completely DX-less.

Checking the band now, during the late afternoon, the noise has gone, though I can still see the occasional weak burst of it. As I type, it's back and almost obliterating Belmont 93.1 - I took a screen grab. Ah, it's gone again. I can hear WDR2 from Kleve on 93.3.

I took some screen grabs earlier too. Hopefully the resolution is OK as I reduced the quality to keep the file sizes low.

Note that either extremity of the waterfall is always black. It doesn't mean there is no noise. It's just the roll-off area.
Attachments
Noise (intermittent) - 2.jpg
Hold your breath .... the noise will attack when it likes!
Noise (gone) - 2.jpg
The noise has gone when I returned home late afternoon. You can see a few meteor bursts at the bottom of the screen.
Noise - 4.jpg
Top of the band. The noise isn't too bad here at the moment, though a sudden burst of it appears for a few seconds. The very top of the band is mostly unaffected.
Noise - 3.jpg
Third quarter of the band. Occasionally, a gap appears around 99 MHz where the noise does not exist. It doesn't last.
Noise - 2.jpg
Second quarter of the band.
Noise - 1.jpg
Bottom of the band.

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John Faulkner, Skegness
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Re: The Noise Is Back In Town!

Post by John Faulkner, Skegness » 23 Feb 2015 19:10

I have discovered two sources of interference and perhaps my findings might be of use.

One is a definite source of wideband noise, right across band 2! While it is less severe at the top end of the band, it is still detectable. It's my Roberts Stream 83i DAB/FM/WiFi internet radio. I think I remember Chris Thatcher telling me about this and it's the reason the FM band appears to be deaf. It isn't actually deaf, but probably more likely to be wiped out by the radio's own internally generated noise. Plug in my external Körner 9.2 antenna and the radio springs to life, though there is still some noise. It's simple enough to cure this problem - just unplug it from the mains!

The second issue is slightly more complicated and I still have some testing to do. It concerns the Fringe Electronics pre-amp I have inline on my desk. Yes, I know it should be on the antenna mast but it has been working so well on the desk behind my computer monitor that I just left it there and forgot about it. By physically moving the pre-amp and Fringe psu around behind the monitor I seem to be able to vary the noise slightly. In fact it still comes and goes by itself without me actually moving it at all, but I wondered if there could be some kind of feedback loop going on as the buzzing I get across the band does sound like some kind of earth loop.

I also tried a different Fringe pre-amp and psu and got the same buzzing noise across the band. Also a Labgear pre-amp was put in place and there was still a buzzing. I didn't think this pointed to anything in particular until I removed all pre-amps and the noise went.

Until I get the pre-amp on the mast I won't know for certain if that is the actual problem.

Can a poorly sited pre-amp induce noise in a feedback loop?

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Re: The Noise Is Back In Town!

Post by satnipper » 23 Feb 2015 21:44

"I removed all pre-amps and the noise went."

"Can a poorly sited pre-amp induce noise in a feedback loop?"

What am I missing here? If you can cause the noise at will by using a pre-amp then the answer to your question must be yes. QED.

Maybe screen refresh from the monitor is being picked-up by the Fringe Pre-amp/PS. Would not have thought it would have that much shielding.

Stuart

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Re: The Noise Is Back In Town!

Post by John Faulkner, Skegness » 24 Feb 2015 00:31

You are very sharp today Stuart and are clearly missing nothing :)

It could well be the monitor, but it hasn't been a problem for the last three months. But there have been a range of minor problems with the monitor in question lately though.

As I hinted, I am aware that the siting of the pre-amp is not ideal. It was a temporary measure and, since everything worked perfectly, I saw no reason to move it. Now would appear to be the time to do just that.

Shame on Roberts though for producing a noisy radio. The psu alone causes interference across band 2!

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