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Old 16th Oct 2020, 3:15 pm   #1
ORAWA01
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Default Strong QRN on the Tropical bands

My QTH has developed this very high level of QRN, static noise on the frequency range of 3.9Mhz - 5.2Mhz recently.

It is very strong and covers the whole part of the stated frequency range. I couldn't hear any signal on the band be it day or night due to the swamp of the noise.

It used to be not as bad as that, but started a few days ago, and now staying quite severe QRN 24 hours a day everyday.

I will get my portable HF radio with the whip antenna out, and go around the house trying to locate the source.

But why does it affect that segment of the spectrum? And what is the likely source? Have you ever come across the similar problem yourself? How did you tackle it?

Thanks
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Old 16th Oct 2020, 3:42 pm   #2
Jon_G4MDC
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Default Re: Strong QRN on the Tropical bands

Maybe someone had their internet connection upgraded to VDSL in your neighbourhood?
I have had no trouble with it but I have heard other stories.

https://en.wikipedia.org/wiki/VDSL#United_Kingdom

Otherwise look around the house for newly introduced equipment powered by wall warts that weigh next to nothing. (switch mode)

Last edited by Jon_G4MDC; 16th Oct 2020 at 3:49 pm.
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Old 16th Oct 2020, 3:54 pm   #3
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Default Re: Strong QRN on the Tropical bands

Have you recently got any new LED lights? I've got a set of 4 above my bench in the workshop, and they make white noise type interference on FM!

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Old 16th Oct 2020, 6:30 pm   #4
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Default Re: Strong QRN on the Tropical bands

QRN is natural noise, I think you have QRM (man made).
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Old 16th Oct 2020, 6:46 pm   #5
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Default Re: Strong QRN on the Tropical bands

I also suspect this is a dodgy SMPSU, or some sort of digital technology like a computer or TV. Have the next door neighbours recently bought a huge OLED TV and mounted it on your party wall?

I once had a laptop charger that appeared to be working normally but was actually chucking out massive amounts of RFI.
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Old 16th Oct 2020, 8:13 pm   #6
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Default Re: Strong QRN on the Tropical bands

Turn off the mains first and foremost to eliminate your end.I am guessing your receiver will run on batteries?
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Old 16th Oct 2020, 9:01 pm   #7
m0cemdave
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Default Re: Strong QRN on the Tropical bands

Does it sound like white noise? And does it start at 3750 kHz? If so, it is probably VDSL signal leakage from somebody's poorly balanced internet connection.
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Old 17th Oct 2020, 10:59 am   #8
ORAWA01
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Default Re: Strong QRN on the Tropical bands

Thank you for the great advice. I suspected the storage heaters in the room and halls, because they were switched on a few days ago. And indeed, when the portable radio with the whip was bright to near the heater, the noise level was going up.

But what was the real source of the noise was, the switching power supply of the old VHF scanner. I took out the old scanner a few days ago, and left powered on for a few days scanning some VHF WX and Marine channels. When the scanner was switched off, the noise dropped drastically. But there was still some noise on the 5 Mhz. When the switching power supply of the scanner was unplugged from the mains, the noise has disappeared totally.

When the scanner was in scanning mode, the noise level was highest.

So, now I know, when the scanner is on, I must switch off the HF radio, and vice versa. It affected from 3.9 - 5.2 Mhz more critically.

But around 1AM last night, I was trying to listen the band again, and the scanner was unplugged, and the band was quiet. But suddenly loud noise came up on one frequency, and it was 4.940 Mhz. It was like loud air plane engine noise, and 59+ just on that frequency.

I failed to know what it was, and just went to bed. I will try to see if it will come up again on the frequency tonight.
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Old 17th Oct 2020, 5:44 pm   #9
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Default Re: Strong QRN on the Tropical bands

For the definition of QRN and QRM, I used to think in terms of the type of noise.

QRN is static noise generated by device or appliance or nature itself.
QRM is for non static noise such as human voice modulation or break through noise from any source.

In the case of OP, I was not aware of the source of the noise whether it was generated by man or nature.

Only thing I knew about the noise at the time was, the type of the noise = static, but not the origin, source or nature.

At the stage, one could be wrong whichever term used between QRN or QRM without knowing the source or nature of the noise, if the definition were based on the source of the noise, i.e. nature or man?
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Old 17th Oct 2020, 6:38 pm   #10
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Default Re: Strong QRN on the Tropical bands

QRN for natural. Thunder storms, atmospherics the sun and imported muck from Jupiter.

QRM for man made. Modulated or not, intentional or not so SMPS, lightbulbs, arc welding, other people's harmonics, harmonic series from telly line output and scan , fridge clicks, ADSL, VDSL, jamming, OTH radars, car ignition, touch-lamps, Spurii from anything.

THe deciding factor is mankind. QRN predated us and will go on after us.

QRM can be stopped if we change what we do.

David
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Old 17th Oct 2020, 11:35 pm   #11
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Default Re: Strong QRN on the Tropical bands

Thanks for the clarification, David.
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