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RFI -- the bane of my ham life




 
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Author Topic: RFI -- the bane of my ham life  (Read 359 times)
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K8DI
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« on: February 28, 2019, 11:26:27 AM »

So this morning I had an empty house, nothing else pressing...

Background:  I don't hear much signal, only noise, on the radio. I have blamed the high noise and bad reception on my crummy antenna. 
Typical noise on 80m is S8-9, same on 40m. All the time.

So today I turned off every breaker but the one going to my radio area (which is also my workbench). Then I killed everything but the power supply for the radios (a big industrial linear supply).

Happily, I found the noise level at S0-S1. turned stuff on, turned breakers on and off, and finally, finally found the culprit...behind the TV in the living room on the other end of the house. An old USB adapter running an Amazon FireStick ( it's not the one that came with it, not Amazon's issue).  This little tiny thing, only when delivering power, blots out EVERYTHING with S9 noise. It is 50+ feet from my radio and antenna.

I did unfortunately also find that my computers in my office also make some noise, but that's like S2-3. Not surprising given that they are data center grade stuff, not home grade. That I will tackle with ferrites, etc. later.

For now, I did some research on the culprit and discovered it is a counterfeit Apple A1265 adapter. Looking back and remembering, it came with a refurbished iPhone off eBay. it is on its way to the landfill.

Maybe I can actually hear the people on the other end, now...

Feeling much better about radio today!

Ed


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Ed, K8DI (fmr. KB8TWH)
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« Reply #1 on: February 28, 2019, 01:42:37 PM »

I also found one of those to be noisy...Luckily, I was listening to the radio the first time I plugged it in and the noise was immediate and loud.....a quick double check and smash with my big boot and into the trash....  Glad you  found it..
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K8DI
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« Reply #2 on: February 28, 2019, 03:21:04 PM »

Before I tossed it into the recycle bin, I opened the broadband noise source up...

No EMI filtering whatsoever.

Chip cap from USB shield to the AC rectifier (should be a Y1 or Y2 rated capacitor).

No distance/space between high and low side (although they did cut a slot).

No way this meets UL or any other safety spec, let alone EMI. Fire waiting to happen.

AC to bridge rectifier through a resistor. Output of bridge has a 3uF cap and then feeds transformer and chip. Transformer secondary to a diode and a 470uF cap. Nothing to snub RF anywhere.

And there are literally hundreds and thousands of these kind of pieces of junk out there...

Ed



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Ed, K8DI (fmr. KB8TWH)
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Nico and Chappie (Chappie is the dog...)


« Reply #3 on: February 28, 2019, 04:16:55 PM »

I did purchase quite a few AC-DC converters from the Chinese manufacturers. Also a lot of LED lamps. The power supplies (12 VDC, 1 A, 2 A, 3A And 5 A) all had de CE test certicate marking and several othe test markings. Indeed all had a place for EMI filtering at the PCB, but none HAD THE PARTS PUT IN.  So it seems that they have the product tested, got the approval and than produce without filters to gain a few cents more.
The LED drivers were all like your charger, no filtering at all. When I switch the light on, no radio and several TV channel gone....
I had to filter all 32 LED lamps in my house, it is not possible to purchase even a single filtered LED lamp in Costa Rica at all. All Cinese sh.....
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W6TOM
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« Reply #4 on: February 28, 2019, 06:34:45 PM »

  I was with the communications department for the local power company for 29 years before I retired. I handled the RFI complaints for the area I worked in, the single largest group to put in complaints were Hams followed by people who had AM radio interference.

   I the course of a year I might handle a dozen complaints and although I did not keep records I did notice that in a large number of cases the RFI was not Power Line Arc Noise. Cheap Chinese switching supply wallwarts and other switching mode supplies were a common cause. If you notice the RFI at even intervals, 25 KHZ, 100 KHz,  (often some multiple of switching supply's frequency) that is a real indicator.

   Operating at my sister's house while I was visiting I had a bad birdie in 3885, it was also every 100 KHz, it was the wallwart for their cordless router.

    Putting your receiver on a battery and shutting off the power is good way to at least determine if the source is in your home. I helped a ham friend with an issue he had, it was the switching supply for his neighbors' CCTV.
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