P3 visualizing local noise

[Fred Atchley]

My P3 started displaying persistent clumps of noise across each band. These
clumps reoccurred at about every 72KH over most bands. I thought I had a rig
problem so I emailed Gary at Elecraft. Based on my description of the
problem he concluded the noise was not coming from the K3 or the P3. He
suggested using a small AM radio to snoop for the source. The source turned
out to be the AC adapter on my son's old laptop! What a relief! If not for
the P3, I may not have taken notice; If not for Gary's suggestion, I may
have given up on trying to identify the "outside" source. I thought I'd pass
this along as another positive WRT P3 integration. It made the difference.

73, Fred

" Do or Do-not. There is no 'Try'..." ~ Yoda

 

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[Jim Brown-10]

On 3/30/2011 11:10 PM, Fred Atchley wrote:
> My P3 started displaying persistent clumps of noise across each band. These
> clumps reoccurred at about every 72KH over most bands.

This is the signature of a switching power supply. They are everywhere,
and most of them are noise RF noise generators. Spectrum displays like
the P3 are very useful in exposing noise sources like these.  You find
and eliminate one and you start seeing weaker ones. The noise comes and
goes and you and your neighbors turn on and off the equipment powered by
these nasty little buggers.  You'll also see them drift up or down in
frequency as they warm up, and drift up and down as their oscillator
frequency is dithered (frequency-modulated by noise).   RFI regulations
limit the field strength at a single frequency. Dithering is a cheat
that makes it easier to stay below those limits by spreading the noise
over the dithered bandwidth.

I recently identified the source of really loud noise on 12M as coming
from the switching power supply for my SteppIR controller.

73, Jim K9YC
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[Kurt Pawlikowski]

Jim, Fred, Et Al,

     Just a note: Some switching power supply "bricks" are noisy, even
if the supplied unit is off. Had a View Sonic monitor like that. Because
I could turn it off, It gave the false impression that it was not the
source: The noise didn't disappear when "off," but some displayed images
did modulate it differently. It wasn't until I disconnected the AC line
that it went away. Unfortunately, that made me "internet" blind, so I
usually just lived with it... {'-)

     Regards,

     kurtt

     Kurt Pawlikowski, AKA WB9FMC
     The Pinrod Corporation
     [hidden email]
     [phone]
     http://pinrod.com

On 3/31/2011 01:30, Jim Brown wrote:

> On 3/30/2011 11:10 PM, Fred Atchley wrote:
>> My P3 started displaying persistent clumps of noise across each band. These
>> clumps reoccurred at about every 72KH over most bands.
> This is the signature of a switching power supply. They are everywhere,
> and most of them are noise RF noise generators. Spectrum displays like
> the P3 are very useful in exposing noise sources like these.  You find
> and eliminate one and you start seeing weaker ones. The noise comes and
> goes and you and your neighbors turn on and off the equipment powered by
> these nasty little buggers.  You'll also see them drift up or down in
> frequency as they warm up, and drift up and down as their oscillator
> frequency is dithered (frequency-modulated by noise).   RFI regulations
> limit the field strength at a single frequency. Dithering is a cheat
> that makes it easier to stay below those limits by spreading the noise
> over the dithered bandwidth.
>
> I recently identified the source of really loud noise on 12M as coming
> from the switching power supply for my SteppIR controller.
>
> 73, Jim K9YC
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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[Craig Smith]

I've also discovered local noise sources from the P3 display - much more
useful than the single frequency response of the K3 alone - a VERY useful
diagnostic tool.

But it gets even better.  I had one switching supply type noise that I
couldn't isolate to anywhere in the shack.  I wanted a portable tester to
carry around the house and possibly outside to find the culprit.  Could have
tried a portable AM radio or used the handy little WinRadio RFI detector.
But wanted something more sensitive and visual, but smaller and more
portable than the K3/P3 combo.  

So used the P3 alone.  Picked a harmonic of the noise that was within the
native frequency range of the P3, set the P3 to a custom IF freq near there,
hooked it to a small 12V gel cel for power and a small loop for a sensing
antenna.  This setup was fairly small and light and completely portable.
Worked great!   Did find the culprit - coming from the microwave oven in the
kitchen.  I now unplug the oven during contests, etc.

73   Craig   AC0DS  



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[Bill K9YEQ]

Craig,  Is the noise constant even while not running it.  I love the idea.
I am tracking down my noise on 2 mtrs, but that has to be done with the K3
and P3 in the shack. Can't wait to find the cause, it is somewhere in the
house.

Not in the shack. Probably computer component generated.  

Bill
K9YEQ

-----Original Message-----


I've also discovered local noise sources from the P3 display - much more
useful than the single frequency response of the K3 alone - a VERY useful
diagnostic tool.
....................
Worked great!   Did find the culprit - coming from the microwave oven in the
kitchen.  I now unplug the oven during contests, etc.

73   Craig   AC0DS  

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[Fred Atchley]

At first I suspected the next door neighbor's solar panel but alas, the
culprit was hiding in my own house. It was an old laptop that was not being
used anymore with its' AC adapter still plugged into the house AC but
disconnected from the laptop.

FWIW, I set the P3 span to max which let me see multiple (3) noise clumps.
This made it obvious that the noise was not random atmospherics. The best
setting on the little radio was the top end of the AM band where there were
no stations (about 1700.)

Kudos to Elecraft all the way around.

 

73, Fred, AE6IC

K3 2241, P3 100

" Do or Do-not. There is no 'Try'..." ~ Yoda

 

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[Bill K9YEQ]

Fred.

Thank you for reminding the radio does low band AM.  I guess I get too much
into the groove.

Bill
K9YEQ


-----Original Message-----


At first I suspected the next door neighbor's solar panel but alas, the
culprit was hiding in my own house. It was an old laptop that was not being
used anymore with its' AC adapter still plugged into the house AC but
disconnected from the laptop.

FWIW, I set the P3 span to max which let me see multiple (3) noise clumps.
This made it obvious that the noise was not random atmospherics. The best
setting on the little radio was the top end of the AM band where there were
no stations (about 1700.)

Kudos to Elecraft all the way around.

 

73, Fred, AE6IC


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[alorona]

I'm sure we could all go on for years listing all of the possible RF noise
polluters that can produce such a distinctive pattern on the screen of the P3,
but while searching your house for a source of RFI do not overlook those stylish
fluorescent undercounter lights in your kitchen (or any other room) that your
wife just had to have, which can really pollute surprisingly badly.

Al  W6LX
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[w0ih]

I had a similar problem not too long ago with a noise that was drowning out lots of the 75 meter band.  I had the LP-Pan at the time (I have a P3 now).   There is a broadcast station several miles from here and the noise made that harmonic so much worse!!

Tracked it down to a cheap Macbook laptop power supply from China.  I took the cord off that was OK and put it on the original Mac supply (which is clean) and it works great.

Moral is don't buy cheap laptop supplied off Ebay.

Mike