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Author Topic: Trying to track down my noise problem.  (Read 452 times)

GREYLINE

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Trying to track down my noise problem.
« on: October 07, 2021, 10:55:27 PM »

I took the advice from this forum and rented a portable generator to run my radio and remote antenna switch with the house breakers off. Unfortunately the noise is still there.

I provided a link to a recording I made with just the radio running off the generator. The noise repeats every 10Khz or so. I haven't noticed it during the day, mostly at night. Can someone identify this noise from the recording so I have an idea where to look next to find the source (powerline, neighbors electronics, etc.)?

https://www.dropbox.com/s/b33pw41f44vc2dz/20211007_221102.mp4?dl=0



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G4AON

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Re: Trying to track down my noise problem.
« Reply #1 on: October 08, 2021, 03:47:39 AM »

If the noise is HF, you could make a DF antenna and trace the source. The flag antenna in March 2021 QST looks pretty useful. The author demonstrates it in a YouTube video too.

73 Dave
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GREYLINE

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Re: Trying to track down my noise problem.
« Reply #2 on: October 08, 2021, 11:03:54 AM »

Thank you, Dave. I plan on getting an MFJ 5008 Directional Noise Finders to hunt it down, but I was hoping someone could at least identify the noise as either powerline or neighborhood electronics based on their experience.
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W9AC

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Re: Trying to track down my noise problem.
« Reply #3 on: October 08, 2021, 11:49:49 AM »

>"MFJ 5008 Directional Noise Finders..."

That's the wrong tool for the job.  The ultrasonic receiver with parabolic reflector is used for narrowly sourcing AC line corona and pole arcs. 

As you discovered, the noise repeats at 10 kHz intervals and is almost certainly from a switch-mode source.  From what?  Nearly everything and anything these days.  The emphasis should never be on "what could it be?"  The emphasis must always be placed on localizing it's direction as a noise source, no matter what it may be.

For the last 10 years, I've been using a portable loop antenna, tablet PC, and an SDR receiver Velcro-strapped to the PC.  An SDR receiver with a panadapter display makes the job much easier while roaming through a neighborhood. 

The tablet PC supplies power for the loop and the SDR receiver.  The loop requires triangulation of the source from two locations but I suspect a lot of on-foot sourcing time can be minimized with a directional loop antenna like this:

https://www.dxengineering.com/parts/dxe-noiseloop

This may be the same loop design that G4AON was referring to.

Paul, W9AC
« Last Edit: October 08, 2021, 11:53:00 AM by W9AC »
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GREYLINE

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Re: Trying to track down my noise problem.
« Reply #4 on: October 08, 2021, 07:42:51 PM »

Hi Paul,

Thank you for saving me from myself!

I will look into the DXE Noise Loop. I've never used an SDR before nor would I know how to interpret the data for the purpose of hunting down interference, but I can read up on it online.

Thanks
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KL7CW

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Re: Trying to track down my noise problem.
« Reply #5 on: October 09, 2021, 12:55:07 PM »

If you have a portable (preferably AM) receiver, you could just try a walk about in the neighborhood, and even without a loop you may get lucky and find the source.  You may even be able to track it down with a regular battery powered AM BCB receiver, however often RFI can travel 1000's of feet or even miles on power lines, etc.  So usually the best approach is to listen to RFI on the highest frequency where you can find it, even at the top of the HF bands, or even something like an AM aircraft receiver at about 120 MHz.  I have used a very cheep thrift store SW receiver which covers several bands of HF and these are probably available for less than $50.  Usually RFI is easier to pinpoint as you go to the higher frequencies.  Naturally a loop will be a great help. 
   I would do two additional things.  Make sure the noise is not from things in the shack.  Also I would temporarily bypass the remote switch and just use a coax jumper, and make sure no wall warts are running anything in the shack.  I have a 6 way remote antenna switch, where the shield connections had about a one ohm resistance.  Picked up 160 meter noise probably from my house, so used a jumper cable, no noise.  Repaired faulty switch design, no noise. So once again....no computers, monitors, etc. just your transceiver right to the antenna for testing.
    Also in is not uncommon for things like solar lights and even the battery back up on your home alarm system to cause RFI. A GUESS is that the noise is a SMPS within a few hundred feet of your antenna, although I cannot guarantee this.          Happy hunting          Rick  KL7CW
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G4AON

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Re: Trying to track down my noise problem.
« Reply #6 on: October 10, 2021, 01:41:52 AM »


https://www.dxengineering.com/parts/dxe-noiseloop

This may be the same loop design that G4AON was referring to.

Paul, W9AC
Yes Paul, that is the one. However, the price is ridiculous. A small preamp is very cheap and easy to make, or you could use one of those wideband “one IC” broadband preamp boards from China on eBay.

I have a 160m to 80m tuned ferrite rod antenna and preamp that I can use with my KX3 or a hand held spectrum analyser by Thurlby Thandar (TTi). A friend built the flag antenna from the ARRL article and says it’s good. A model of it in EZNEC shows a good rear notch up to 20m, a smaller version would probably give a good notch higher.

Most of the noise around me is on 80m and is spread along overhead telephone wires, plus a lousy solar panel system with a Chinese made SolarRiver 4KW inverter that puts out spurs every 20 KHz across 80m and 6m. The solar system was easy to DF.

73 and good luck with your direction finding
Dave
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N2QLT

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Re: Trying to track down my noise problem.
« Reply #7 on: October 10, 2021, 11:36:43 AM »

Betcha when you find it, the label on it says "made in" you-know where.....
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N1UR

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Re: Trying to track down my noise problem.
« Reply #8 on: October 11, 2021, 04:02:38 AM »

I use a small Yaesu HT with 420Mhz AM listening capability and a 6 el yagi - handheld.  You need to start with some direction in mind from your station and preferably a beam heading.  "Notch" the direction for highest accuracy.  Haven't missed yet with that set up.  Boat all the pieces at a hamfest for under $100.

I always start with killing the house power and listening on HF with battery power.  If that doesn't kill it then try and get a bearing from the shack.  If its radiated powerline noise, that direction my just be to the nearest powerline.  And then its "walking the line" time.  The noise can be up to 2 miles away in either direction but usually a lot closer.

Ed  N1UR
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GREYLINE

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Re: Trying to track down my noise problem.
« Reply #9 on: October 11, 2021, 10:14:54 AM »

Great tips, guys. Thank you!

I have an Pixel RF-Pro-1B RX loop and I get a small null in the noise which gives me at least an idea of the direction. I also have a small portable SW radio that has the aircraft band. Unfortunately the antenna is just a small whip on the back, but I will wait for the noise the show up and then drive around and see if I can find it. I'm on a city lot with above ground power lines, so it's probably a rats nest of noise, but I will definitely try your suggestions.
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KL7CW

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Re: Trying to track down my noise problem.
« Reply #10 on: October 16, 2021, 01:09:16 PM »

The QST flag antenna looks like it would work on the HF bands and possibly higher.  It may even work good enough without a preamp on your portable SW receiver if you could take off or telescope down the whip and hook it up to coax and a ground somewhere in the radio, possibly the earphone jack shield or the negative battery terminal, or whatever.
Many of these inexpensive SW receivers have very good sensitivity.  You could even put the radio inside a shield cage made of wire mesh and feed the loop output into the coax via coax.  Lots of good preamp circuits to build, or even buy one on ebay. The null off the back of the flag, should be much more useful than the very broad peak in the front.  I have a RX array of flag antennas.  Use them on 160 and 80 meters, but still directive up to over 14 MHz.  The small flag in QST should be better than my flag on the higher HF bands as well.
                    Good Luck  Rick  KL7CW
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KL7CW

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Re: Trying to track down my noise problem.
« Reply #11 on: October 17, 2021, 10:04:48 AM »

I highly recommend the W7IUV preamp.  I built mine, but the kit is a better idea since I needed to design my PCB and obtain a rather rare transistor and all the parts.  I use mine on an array of flags.  I tried some other preamps, even experimented with different bias, etc. but still got some nasty BCB intermod on 160 meters.  No problem with the W7IUV circuit.  Also it is claimed that this preamp is rather husky and is not easily damaged by TX from a near TX antenna. If you build the QST loop and a good preamp, after you find your noise problem, it might just happen that the little loop/preamp might be useful as a RX antenna on 160, 80, and possibly higher to "null" noise from a single particular source, like a neighbors house.  Now the 2 to 3 S unit F/B ratio may not be enough, but it could help.  My flags and preamp work really great for BCB DX'ing, but my flags are larger.  Also the 20 dB preamp is plenty for me since I have larger flags and good preamps in my RX, but you might need something like 30 or 40 dB of preamp gain.  I do operate my preamp at the full 12 volts (for better intermod performance) and it does draw significant current, so a 9V small battery would not last long.  Happy experimenting  Rick  KL7CW
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