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Author Topic: Carrier (RFI) every 30Khz ??  (Read 11935 times)
G8CVF
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Posts: 35




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« on: September 14, 2015, 02:42:00 AM »


Hi thanks for the interest.

I am plagued by a strong carrier (RF) every 30Khz throughout all bands, if I remove the antenna it disappears proving it's external however in desperation I have switched everything off in my house except the Transceiver of course and it stays on. It's a very stable carrier too it's the 30Khz spacing that has me stumped.

This has been a pest since I moved QTH. I don't want to start knocking on peoples doors until I have some idea what may be causing this 30Khz phenomenon i.e a psu, tv or the neighbors cat.

Any idea would be appreciated as this is a real pain in the butt.

Regards

Peter
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NK7Z
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Posts: 1532


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« Reply #1 on: September 14, 2015, 03:30:20 AM »

More than likely a switching supply.  That does not narrow the field much, but that is about all that can be deduced from the information given...  I have a few articles at: http://nk7z.net/category/info/mitigation-of-rf-interference/ covering location, and mitigation of RFI...  You want to look at the second article down from the top there.  It is called quantification, and it lists a number of useful tools and procedures to help quantify what you have...
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Thanks,
Dave
For reviews and setups see: http://www.nk7z.net
G8CVF
Member

Posts: 35




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« Reply #2 on: September 14, 2015, 04:05:52 AM »


Thanks Dave,

I have been searching for the answer for ages and actually by chance came across your articles, being an old timer to radio I am quite au fait with switch mode power supply interference but as they don't use 'actual' tuned circuits except by accident I have dismissed them in favour of 'something' in the area that uses a tuned circuit and what I receive is a multiple or otherwise of this generated RF, its the stability that has me foxed, SMPS units usually generate hash as opposed to a stable RFI, (I am to assume).

Thanks for your ideas.

73
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NK7Z
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« Reply #3 on: September 14, 2015, 05:15:25 AM »


Thanks Dave,

I have been searching for the answer for ages and actually by chance came across your articles, being an old timer to radio I am quite au fait with switch mode power supply interference but as they don't use 'actual' tuned circuits except by accident I have dismissed them in favour of 'something' in the area that uses a tuned circuit and what I receive is a multiple or otherwise of this generated RF, its the stability that has me foxed, SMPS units usually generate hash as opposed to a stable RFI, (I am to assume).

Thanks for your ideas.

73
I would tend to agree with you on this, however, I have a few that are dead stable after being on for a few hours...  One is a grow operation several thousand feet from me, which starts up gogin all over the place, then after a few hours settles down and is almost the same day in and day out...  Not very loud anymore, since we contacted him...  I think he changed lights...  In any case, good luck!
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Thanks,
Dave
For reviews and setups see: http://www.nk7z.net
KF7CG
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Posts: 1130




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« Reply #4 on: September 15, 2015, 10:06:01 AM »

Could it be a plasma or other similar display with a higher than original horizontal sweep frequency. Old televisions were at 15,750 hertz and extremely steady and that was with 640 pixel horizontal by 480 pixel vertical resolution. If it were a high power high resolution display it might generate many harmonics at higher frequency spreads.

I no longer have a list of horizontal sweep frequencies for the old CRT monitors or their plasma replacements, but this might be a place to look.

KF7CG
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G8CVF
Member

Posts: 35




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« Reply #5 on: September 16, 2015, 08:04:17 AM »

Could it be a plasma or other similar display with a higher than original horizontal sweep frequency. Old televisions were at 15,750 hertz and extremely steady and that was with 640 pixel horizontal by 480 pixel vertical resolution. If it were a high power high resolution display it might generate many harmonics at higher frequency spreads.

I no longer have a list of horizontal sweep frequencies for the old CRT monitors or their plasma replacements, but this might be a place to look.

KF7CG

Hello Thanks for your ideas.

I must say a TV was the first thing I thought about as I live in a very small cottage in a tiny terrace so I know if/when my neighbours are about but the RFI is still there when they are out and in the middle of the night when they are all tucked up and dreaming.

I don't think I'm going to solve this RFI and unfortunately I don't have a portable HF receiver to go out DF-ing the problem.

Think I'll put this to bed in a day or two.

Thanks to all.......
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K1ZJH
Member

Posts: 2952




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« Reply #6 on: October 17, 2015, 06:27:14 AM »

Put you receiver on CW or SSB, and listen to the beatnote on any of the 30 kHz signals.  Is it raspy, or a clean hetrodyne with no raspiness or drift?

If it is power supply, you are probably hearing harmonics--those supplies offern use a square-wave in the 30 kHz region. Being a square-wave, the harmonics will go on forever.

Pete
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K2OWK
Member

Posts: 1205




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« Reply #7 on: October 17, 2015, 03:37:27 PM »

Check for electric fence. They put out the type of interference you are talking about if not installed properly.

Hope this helps,

73s

K2OWK
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WA2ISE
Member

Posts: 913




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« Reply #8 on: October 17, 2015, 03:48:38 PM »

Wired ethernet (cat 5) creates birdies every 60 or so KHz.  Might be 30KHz if your antenna is really close to a run of ethernet cable.  Try shutting down your routers and computers and see if that makes any difference. 
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WB6RJH
Member

Posts: 2




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« Reply #9 on: June 27, 2016, 04:47:35 PM »

I just ran into this, decided to take the DFing route using an HT (Kenwood TH-F6A) that I tuned to one of the harmonics that was causing me grief (in my case, 28.316 MHz).  Walked around the garage and house, was surprised to find that a couple old Apple Airport Express units were howling.  These were older units that I'd retired from WiFi usage, have just been using them plugged into the wired ethernet (WiFi disabled) with the TOSLINK optical outputs going to stereo systems that are not otherwise networked.  I unplugged the one in the house, over a hundred feet away from the shack, and the noise went way down.  I then unplugged the one in the shack and the noise went down further.  The more recent Airport base stations don't howl.  I did find that an old Roku unit in the house was making a fair amount of noise, too, so I unplugged it.  Amazing how much of a problem these "hockey puck" units can make!  Later I'll see if I can mitigate the RFI with clamp on ferrites or even toroidal ferrites with a number of loops through them, on power lines as well as on the wired ethernet cables on the hockey pucks.  Now I find that the ethernet switch in the shack is responsible for the residual noise; I'll have to see about reducing that with ferrites but the noise level is livable now.

73,
-Sam, WB6RJH
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WB6RJH
Member

Posts: 2




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« Reply #10 on: June 27, 2016, 05:17:33 PM »

Wow, figured out that it's not necessarily the ethernet switch in the shack but the laser printer!  Tried swapping in a totally different ethernet switch, no change.  But unplugging the printer's ethernet cable eliminates the noise, even if the printer stays on.  As another poster indicated, ethernet (at least on some devices) can certainly be a source of significant RFI.

73,
-Sam, WB6RJH
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WA2ISE
Member

Posts: 913




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« Reply #11 on: June 30, 2016, 12:32:28 PM »

... But unplugging the printer's ethernet cable eliminates the noise, even if the printer stays on.  ...

Maybe using a shielded ethernet patch cable would contain that RFI (I'm assuming the printer is near a router or switch, making for a short length of cable).

I have an inkjet printer that I found I need to shut its power off unless I need to print something.  Else it will go off into lalaland after a few hours. 
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