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Author Topic: Any ideas on this QRM?  (Read 526 times)

AE8GS

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Any ideas on this QRM?
« on: October 28, 2022, 05:09:45 PM »

This started at 12:30 pm local time (EDT), and is still going at about 8:00 pm local. The interval between the "carriers" is about 30-31 kHz through all of HF, at least. I looked at 31 kHz and saw nothing.

Reception is still fine between the QRM, and you can see I am tuned to a SSB signal.

If I disconnect my antenna the QRM disappears, but with just a 12 inch piece of wire for an antenna, I get it (along with a few very strong stations).  So I think that rules out my receiver but makes it local.

Next step is to cut power in my house (maybe I leave one circuit on for my rig, or if I am feeling energetic I could run it off a 12 voltage battery). I live in a suburban housing, so plenty of opportunities for nearby noise sources.

The link below is to a picture of the spectrum display on my rig.

https://imgur.com/Ttjm9kz

BTW, I have seen that "swishing" on the spectrum display before and always wondered what it was (I'm a new ham). But I have never had these very strong "QRM harmonic carriers" before.
« Last Edit: October 28, 2022, 05:14:21 PM by AE8GS »
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KG4LAC

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Re: Any ideas on this QRM?
« Reply #1 on: October 28, 2022, 05:15:05 PM »

Based on the screenshot appears bad.

Perhaps, same as what I recently experienced?

https://www.eham.net/community/smf/index.php/topic,137197.msg1273876.html#msg1273876
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N2BFJ

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Re: Any ideas on this QRM?
« Reply #2 on: October 28, 2022, 07:48:50 PM »

Check any battery chargers you may have. Chargers, often when they go into "pulse mode" can emit some
nasty interference. I have had that problem several times.
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WB0CJB

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Re: Any ideas on this QRM?
« Reply #3 on: October 28, 2022, 08:59:49 PM »

The 31 kHz noise spacing might be a nearby computer monitor, possibly from a gaming system? Given the amount of time its present maybe someone is playing video games. Just a thought...

Paul WB0CJB
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AE8GS

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Re: Any ideas on this QRM?
« Reply #4 on: October 28, 2022, 09:04:08 PM »

FOUND THE CULPRIT! We have some low power decorative lights in some kitchen cabinets with glass doors. Hidden inside is a box about the size of a laptop power supply, and it feeds a string of LED lights, which are daisy chained, and all told are maybe 10 feet long. There is a remote (probably IR) and they are dimmable as well.

I imagine there is a  switching power supply and it might be modulating the LEDs as well, and that 10 foot string radiates the noise.

We rarely use them, but for some reason my wife turned them on today. Later in the day when I noticed the noise disappeared, after she had turned them off, the penny dropped.

Thanks to everyone with their suggestions. I would have eventually found it by turning off the power breakers one-by-one.
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KT4WO

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Re: Any ideas on this QRM?
« Reply #5 on: October 30, 2022, 04:39:55 AM »

Switching PS are evil!!! 
Long live my RS-35 and RS-70   hahaha
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KH6AQ

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Re: Any ideas on this QRM?
« Reply #6 on: October 30, 2022, 11:26:53 AM »

The fact that it "swishes" -- moves about in frequency -- tells us it is not a computer monitor or any other crystal controlled oscillator. It points to a switching power supply as you discovered. The two easy fixes are to leave the decorative lights off. That is how I "fixed" the LED lamp noise from our ceiling fans. 
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KD6VXI

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Re: Any ideas on this QRM?
« Reply #7 on: November 01, 2022, 04:38:07 AM »

The fact that it "swishes" -- moves about in frequency -- tells us it is not a computer monitor or any other crystal controlled oscillator. It points to a switching power supply as you discovered. The two easy fixes are to leave the decorative lights off. That is how I "fixed" the LED lamp noise from our ceiling fans.

Most computer monitors now use a switching power supply.  This has been the case since we moved from CRT based monitors.

Some are worse than others.  I've found Dell and Acer to be pretty darn quiet.

Also, if you get them in 12v input versions (K9YC has the make and model he found, I believe Acer, but could be wrong) that have direct 12v input.  Those are virtually quiet when powered from the station power supply.

--Shane
WP2ASS / ex KD6VXI
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