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Lowering My Noise Floor
#1
Lesson learned: My laptop power supply was adding 4 S units to my noise floor through my CAT control cable to the radio.

I was moving some cables around in my shack last night in an attempt to tidy things up a bit. When I unplugged my CAT control cable from my laptop, the noise floor on my radio dropped 4 S units on 80M (I just happened to be logged into an 80M net). I plugged it back in and the noise came back. Snap on ferrite beads did not help. So I plugged the cable into the USB port on my Apple macbook and there was no noise. This told me that it was not the cable, but a problem with my windows laptop. Next I unplugged the power supply from my windows laptop and the noise disappeared. I unplugged the power supply from the power outlet and the noise disappeared. After plugging it back it, all was quite for about two seconds and then the noise returned. This told me that the power supply was generating RFI after the charging circuit turned on. I had two snap on ferrite beads sized for coax and wound three turns on each, but still there was noise. Fortunately, I had purchased a large type 43 torroid for a balun project a while back and made 10 turns on the cable from the power supply to the laptop. The noise has now disappeared!

I hope this might be helpful to others in the same situation. Unplug your power supply from the wall outlet and see if your noise floor drops on any of the bands. Picture attached.

73,
Joe


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#2
(12-18-2014, 10:41 PM)KC1BAQ Wrote: Lesson learned: My laptop power supply was adding 4 S units to my noise floor through my CAT control cable to the radio.

I was moving some cables around in my shack last night in an attempt to tidy things up a bit. When I unplugged my CAT control cable from my laptop, the noise floor on my radio dropped 4 S units on 80M (I just happened to be logged into an 80M net). I plugged it back in and the noise came back. Snap on ferrite beads did not help. So I plugged the cable into the USB port on my Apple macbook and there was no noise. This told me that it was not the cable, but a problem with my windows laptop. Next I unplugged the power supply from my windows laptop and the noise disappeared. I unplugged the power supply from the power outlet and the noise disappeared. After plugging it back it, all was quite for about two seconds and then the noise returned. This told me that the power supply was generating RFI after the charging circuit turned on. I had two snap on ferrite beads sized for coax and wound three turns on each, but still there was noise. Fortunately, I had purchased a large type 43 torroid for a balun project a while back and made 10 turns on the cable from the power supply to the laptop. The noise has now disappeared!

I hope this might be helpful to others in the same situation. Unplug your power supply from the wall outlet and see if your noise floor drops on any of the bands. Picture attached.

73,
Joe

Rich would be the expert here on Laptop Power Supply noise.
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#3
I'm sure for less than $1/unit the manufacturer could fix the design.
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#4
Coincidently, I heard a guy rag chewing on 17M today and he was telling his friend how bad a lot of PC power supplies are built and that he has had several to generate a lot of RFI on 80M.

73,
Joe KC1BAQ
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#5
I get PC noise on 40M & 80M. PC's are notoriously noisy. Many ferrites in this shack (for RF in the shack). I also installed AC line filters on them but haven't made any conclusive discoveries as to their effectiveness.

At least my SMPS isn't noisy.
K1RCT - Rob
W1NRG Station Activities Manager
Home Email

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#6
My dimmer in the shack is sometimes a source of QRM, but not all the time (so sometimes I'm in the dark). My high performance video editing platform PC is troublesome at times. No noise floor increase until I launch some applications. Noise floor pops up a little but not a lot. I played around a bit using a laptop for my logging PC verses my 'desktop' video platform but no significant reduction in noise floor. Looking for that Faraday cage.

steve
73, Steve - KC1SA
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#7
Well I discovered ONE source of noise: My "FCC Compliant" Plasma Display.

Tuned up XE1/DJ4EJ on 21270 today. I could hear him well, an S5 easy. Then Stuart fires up the Plasma and a game. Noticed the noise but didn't make the 'connection' until I heard changes in the phase of the noise. Then I turned and watched Stuart playing his PS3 FPS Game and immediately noticed correlation between his FPS view and the noise phase and/or intensity.

I shut down the Plasma (42") and zero noise!

So Rich, Jim: have any suggestions? Yeah I could shut off the set, I own the stupid thing but that would create other problems. I've seen MFJ makes a noise reducer with decent reviews, as does JPS (NIR-12).

Anyone have any suggestions?
I could build a Faraday Cage for my Station! That would be actually less problematic than shutting off the set!
K1RCT - Rob
W1NRG Station Activities Manager
Home Email

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#8
[b]
(12-28-2014, 01:53 PM)KC1ACN Wrote: Anyone have any suggestions? ....

In a word fugetaboutit.
(Ask GNV from Lawn Guyland to provide the etymology.)
I wrote a Key Klix article in Dec 2011 on the subject with a cause summary and some suggested cures. Since you have identified the source, I suggest a case of Coors Silver Bullets and play Lone Ranger during the Super Bowl.
73, Dan
<<I tried to attach the KK article, but it didn't work. So here is the text part "A 21st Century Windmill. Amateur radio operators may be seen as an odd group. Terms like grounding, shielding, and interference are almost unknown to the general public – save discussions of this weekend football games – but are a constant consideration and bane to hams. Hams may often be seen turning appliances on and off, touring the neighborhood with an AM radio or noise sniffer, looking for errant sodium street lamps, or jotting down utility pole numbers; all to reduce their receiver noise level one or two S units. To the observer, it may be like Don Quixote chasing windmills. Behind a few of those windmills, hams often find some true interference sources. Faulty power transformers, leaky cable TV distribution deteriorating street lights, and even some residential switches or appliances that are ready to burst into flames. Hams often work with the source owners to identify, educate and correct the problem. Gee, what a perfect world we live in!
A few years back, a new windmill appeared on the horizon. The Plasma TV hit the market in the 19??s and brought innovations not imagined in a CRT world. Plasma TVs introduced flat screen projection surfaces, large viewing screens (the reported largest is 150 inches), debatably a near perfect and natural video, and a very thin depth profile. Due to the very high cost (over $10K) of these early units; they were mostly restricted to sports arenas, conference venues and similar locations. Recently some Plasma TVs have been appearing in your neighborhood; the home entertainment center, the “man-cave” or the corner sports bar.
So what is this modern interference windmill? Plasma TV units, along with their enhanced video capability, have been documented as a massive interference source. The plasma, a gaseous film is excited by a frequency variable signal causing the photons in the gas to ionize in a variety of spectral pixels. The plasma is sandwiched between two conductive plates; the front plate is transparent and contains a nearly invisible conductive grid. The Plasma TV screen may be visualized as a giant capacitive antenna operating at or near the dielectric breakdown range of voltage and frequency.
There are many, many reports of an RFI buzz from these sets. The digital interference noise is most prominent on the lower bands; 160 is a pure disaster, but all of the HF bands are affected with noise levels reported at S3 to S5 on 40 meters. The reports are especially prevalent in the CW portion of the HF bands. Are brass-pounders more critical or are phonies just more tolerant and deaf? Of course, if the offender is in your own abode, then you have to deal with it. But offensive reports have been noted from Plasma sets in neighboring sets up to a quarter mile away. These friendly neighbors are not likely to be willing to trade-in their monster set, change their viewing times or allow a reflective mesh housing around his multi-$K toy. Manufacturer brand and location do have an impact, at least to some extent. Some enterprising hams have built a Faraday shield around their shack to fend off this ionization intrusion – a big effort not available to all. Some brands seem to be more offensive, while others do a better shielding job.
There is a cohort that claim this consumer interference problem is an anomaly that hams will live through as they have survived assaults before. Logically, there may be some credence to this thought. In the past couple of years, some of the Plasma TV sets coming on the market have a much lower noise pollution factor – maybe a result of a multitude of customer complaints. Availability of competitive or lower cost alternatives, such as LCD and DPL sets, that have lower noise signatures. On the down side, manufacturers claim that Plasma TV units have about a 20 year (10,000+ hours) expected life. How long did all those old B&W sets kick around?
Was that a mumble about Part 15 out there? Don’t count on it! The FCC is either unable or unwilling to effectively police this interference source. In many cases, the manufacturers legally conform to the letter of the Part 15 rules, but can legally circumvent its effective application in the delivered product. Also, most of the end users of this entertainment device really don’t care about your inability to break into that DX pileup.
If a Plasma TV is on your Christmas list, you may want to make a change. If your neighbor is the owner or potential owner, you may be left – at least for the present time – to changing your on-the-air schedule or hope your offending neighbor tosses a beer can through his man-cave screen during the Super Bowl. GD
>>
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#9
I'm seriously considering the use of a cup of coffee with sugar. Plenty of sugar to increase the carbonizing effect of catastrophic arc decomposition of conductors in a 'certain' appliance.
K1RCT - Rob
W1NRG Station Activities Manager
Home Email

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