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Author Topic: Tracking down any possible local noise.  (Read 340 times)

5BWAZ

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Tracking down any possible local noise.
« on: November 06, 2020, 08:48:44 AM »

Hello,

I've read that to find any noise coming from you house you should turn off all power and run an HF rig off battery power and check for noise. Turn on one breaker at a time to pin point any noise source. The problem is I don't have a battery powered rig. I do have a small AM/FM/Shortwave radio with telescoping antenna. Will that work? Id so, is there a particular frequency range that is best to monitor? Would this small radio work tracking down noise sources around the neighborhood like power poles?
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WA2ONH

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73 de WA2ONH  <dit dit> ... Charlie
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"Never be satisfied with what you know, only with what more you can find out."
   Dr David Fairchild 1869-1954 US Scientist

W4NBO

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Re: Tracking down any possible local noise.
« Reply #2 on: November 06, 2020, 11:07:29 AM »

As WA2ONH was indicating i think, building up your knowledge base on this topic is your #1 weapon. Lots of stuff to read online and groups on this topic. Turning your house power would give you some evidence with your radio to proceed further. To try to answer your question, yes the small radio you have will work to find some sources but not as well as other receivers with a more wide range of frequencies and directional antennas to pinpoint the source of more difficult rfi. Powerline RFI tends to get weaker as frequency increases thus being able to increase frequency is most helpful on difficult sources. But on easier to find sources the small radio is just fine.

Recently I had a powerline source to die on its on. I knew it was powerline rfi due to seeing the 120 per second pulses by viewing the audio. I also knew with about 90% certainty what pole by tracking with my FT817 and various homebuilt directional antennas. After that tracking down another rather narrow source on 80m with a small AM radio. Turned out to be my front porch light strobing with an LED bulb in it. Replaced the photocell with an LED friendly one cured that. And some birdies I am currently working on being caused by CAT5's out of my routers. Toroids for that. Just suspected birdies were data so unplugged the routers to find. Those are some examples but RFI is a big topic that one could write large books on I suppose and still not cover it all.

73
Chuck
AF4O
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VK3OD

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Re: Tracking down any possible local noise.
« Reply #3 on: November 06, 2020, 08:04:15 PM »

Its always advisable to track down the noise on  the frequency that you are receiving the noise on.

Noise is rarely correlated across  a wide frequency range. Start and track the noise on the frequency with  the highest noise level that annoys you. I have frequently tracked switched mode power supply noise like that from LED light power supplies that only exists on 1 or 2 HF bands and nowhere else on HF/VHF. Rarely does this interference extend into the AM broadcast band or into the VHF/UHF ranges. Noise heard on the broadcast band is rarely heard on the HF bands.

Arcing noise from power lines very rarely extends into the Lower HF ranges. It may exist on Airband, 2 meters, and 440 mhz and rarely be detected on HF. Its only under exceptional circumstances that VHF/UHF arcing noise  is detected in the HF range in my experience. 

The most frequently encountered broadband emitter these days is powerline ethernet adapters that can be heard right across the HF and VHF spectrum, the notches in the ham bands does help but there is still detectable levels of interference.

Likewise even monitoring high levels of arcing noise in the  AM broadcast band rarely does this same noise even migrate to the 160 meter and 80 meter band.  There are no hard  rules for QRM/RFI and I am only speaking from my anecdotal experience of tracking down noise for a couple of years now. Its almost a second hobby that is required these days if you are a ham operating on HF such is the dismal failure of our self regulating EMC regulations.

A small portable shortwave receiver with a telescopic whip is going to make your life very difficult. Even a coat hanger bent into a 40 to 50cm loop  plugged into the external antenna socket of your shortwave receiver will make nulling and finding the noise much easier. The best tool for the job is a tuned loop antenna from 40cm to 60cm  in diameter.

In my car I have my QRM tracking receivers set up for spot frequencies where I can monitor them all simultaneously from LF through to the UHF band while monitoring in AM mode. Rarely is the noise correlated across the MF/LF/HF/VHF/UHF frequency range. 

It seems that a 50HZ powerline frequency produces less wideband  intense arcing that spreads noise across the HF spectrum. I routinely monitor on AM for arcing power line noise  and I rarely find it. It maybe a combination of factors  which includes no salt on the roads, less moisture, different mains frequency and different hardware designs on the power poles that makes the likelihood of arcing less apparent here in Australia. I rarely see the kind of HF frequency arcing that I see in the videos of people tracking powerline noise in the USA for example. The biggest trouble maker is switch mode power supplies in all the electronics gadgets and things such as battery chargers and LED light power supplies which cause bad and intense QRM from a very long distance away.

I also have an ultrasonic dish and must admit its the least useful of the tools  required to track noise because arcing insulators and pole hardware is very rare down here in Australia and this may well be related to the dry hot climate. The other point is that heavy rainfall  where I live is rare  so arcing  cant be  only caused by things like dirty, dusty or faulty hardware.

I am not an expert in the field and all of the above is anecdotal observations rather than scientific expert opinion.

73
Craig
VK3OD

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W0RW

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Re: Tracking down any possible local noise.
« Reply #4 on: November 07, 2020, 05:09:10 AM »

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