Want to see how bad a Chinese unbranded wall wart can be? Check out this
article I wrote in 2025. As Dave W0LEV said, no line or output filtering.
https://www.edn.com/using-the-arduino-cpu-to-demonstrate-re-and-ce/
<https://www.edn.com/using-the-arduino-cpu-to-demonstrate-re-and-ce/>
______________________
Kenneth Wyatt
wyattphoto@mac.com
> On Sep 25, 2024, at 3:35 PM, rfi-request@contesting.com wrote:
>
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> Today's Topics:
>
> 1. Re: wall warts and shielding the DC side - theory?
> (David Eckhardt)
> 2. Re: wall warts and shielding the DC side - theory? (Wes Stewart)
> 3. Re: wall warts and shielding the DC side - theory? (Jim Brown)
> 4. Re: wall warts and shielding the DC side - theory? (Jim Brown)
> 5. Re: shielded Ethernet cable, or not (Jim Brown)
> 6. Re: wall warts and shielding the DC side - theory?
> (David Eckhardt)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 25 Sep 2024 17:09:18 +0000
> From: David Eckhardt <davearea51a@gmail.com>
> To: Greg Troxel <gdt@lexort.com>
> Cc: rfi@contesting.com
> Subject: Re: [RFI] wall warts and shielding the DC side - theory?
> Message-ID:
> <CAODdWWHdXOuVw-eOHTuzqHrnvjbeLUFvR0DnDes7yjoAJ6b6vQ@mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
>
> The typical wall wart from China (the vast majority of them) contain no
> decoupling or choking on either the input or output. Sure, they carry all
> the required regulatory markings, but they are bogus from China with no
> testing or evaluation wrt RFI/EMC. Them's are the facts of today.
>
> The RFI, as you may realize, is generated internally due to the switching
> power conversion. The days of RFI quiet real transformers which contain
> iron and copper are unfortunately gone.
>
> One side connects to the grid and the other, DC or LV side, connects to
> your equipment. Any appropriate ferrites clamped onto either side will do
> some good. But realize, ferrites are a band aid. The Chinese engineers
> and suppliers do not spend additional funds on the wall warts to alleviate
> RFI. Again, them's 'r do facts of ta'day.
>
> Dave - W?LEV
>
> On Wed, Sep 25, 2024 at 3:49?PM Greg Troxel <gdt@lexort.com> wrote:
>
>> I'm writing to ask a theory question about an aspect of RFI management
>> that I have always been unclear on.
>>
>>
>> Consider a device connected to L and N from a 120V outlet, and having a
>> 0/+12 cable to some other small device. I understand that common mode
>> current on either the DC cable or the AC wiring will radiate, and that
>> choking impedance is the right answer.
>>
>> Thinking about building a transmitter, it seems tricky for common-mode
>> current to be efficient if it isn't sort of balanced on the two wires.
>> Otherwise, it's sort of an end-fed antenna. Therefore, having an
>> effective choke on the DC cable, even with no choking impedance on the
>> AC side, should greatly reduce the current on the AC wiring. This is
>> pretty much all you can do if the device has a plug and not a power
>> cable, unless you use a choked extension cord.
>>
>> My questions
>>
>> - Is the above analysis iscorrect or confused?
>> - If confused, does choking the DC cable side mostly address the RFI
>> issue, by some other mechanism?
>> - What is the equivalent circuit that explains generation of
>> common-mode current?
>>
>>
>> A related question is that given a physically small device that plugs
>> in, how are these able to generate common-mode current, given the lack
>> of a counterpoise for an endfed (which is of course not quite endfed,
>> but very off center)?
>>
>> 73 de n1dam
>>
>> _______________________________________________
>> RFI mailing list
>> RFI@contesting.com
>> http://lists.contesting.com/mailman/listinfo/rfi
>>
>
>
> --
>
> *Dave - W?LEV*
>
>
> ------------------------------
>
> Message: 2
> Date: Wed, 25 Sep 2024 18:06:41 +0000 (UTC)
> From: Wes Stewart <n7ws@yahoo.com>
> To: Greg Troxel <gdt@lexort.com>, David Eckhardt
> <davearea51a@gmail.com>
> Cc: "rfi@contesting.com" <rfi@contesting.com>
> Subject: Re: [RFI] wall warts and shielding the DC side - theory?
> Message-ID: <1382522686.6535404.1727287601022@mail.yahoo.com>
> Content-Type: text/plain; charset=UTF-8
>
> Jameco still sells analog wall warts.
>
> On Wednesday, September 25, 2024 at 10:11:51 AM MST, David Eckhardt
> <davearea51a@gmail.com> wrote:
> The days of RFI quiet real transformers which contain
> iron and copper are unfortunately gone.
>
> ------------------------------
>
> Message: 3
> Date: Wed, 25 Sep 2024 11:43:13 -0700
> From: Jim Brown <jim@audiosystemsgroup.com>
> To: rfi@contesting.com
> Subject: Re: [RFI] wall warts and shielding the DC side - theory?
> Message-ID:
> <3f6dec29-818d-40ad-be1c-2e7fc39fb222@audiosystemsgroup.com>
> Content-Type: text/plain; charset=UTF-8; format=flowed
>
> On 9/25/2024 10:09 AM, David Eckhardt wrote:
>> The RFI, as you may realize, is generated internally due to the switching
>> power conversion. The days of RFI quiet real transformers which contain
>> iron and copper are unfortunately gone.
>>
>> One side connects to the grid and the other, DC or LV side, connects to
>> your equipment. Any appropriate ferrites clamped onto either side will do
>> some good.
>
> Not quite. I don't know of any ferrite parts that by simply clamping
> them onto cables will do much to reduce radiation of RF trash below VHF.
> Ferrite parts are parallel resonant devices, and for most "suppression"
> parts, that resonance is in the VHF range, simply because that's where
> meaningful FCC Rules kick in. To be effective at HF or MF, multiple
> turns must be wound through the effective part to lower the resonance to
> the part of the HF spectrum where suppression is needed. Thanks to the
> nature of currently available products, which exhibit relatively wide
> manufacturing tolerances, the only REPEATABLY effective ferrite material
> I know of (and I've been looking for 20 years) is Fair-Rite #31. It is a
> MnZn material, with relatively low Q. Thanks to mfg tolerances, the Q of
> NiZn materials is too high for repeatability of designs/recommendations.
>
> An engineering development and tutorial of all of this is in
> k9yc.com/RFI-Ham.pdf
>
> I strongly agree with everything else in David's excellent post.
>
> But realize, ferrites are a band aid. The Chinese engineers
>> and suppliers do not spend additional funds on the wall warts to alleviate
>> RFI. Again, them's 'r do facts of ta'day.
>
> Another important point -- the LAST thing we should be doing is going
> "inside the box" of an existing product. Anyone who's been involved with
> product development knows that there are a lot of detailed decisions
> that can interactively cause things to go much further south. :)
>
> 73, Jim K9YC
>
>
>
>
>
>
>
> ------------------------------
>
> Message: 4
> Date: Wed, 25 Sep 2024 11:57:27 -0700
> From: Jim Brown <jim@audiosystemsgroup.com>
> To: rfi@contesting.com
> Subject: Re: [RFI] wall warts and shielding the DC side - theory?
> Message-ID:
> <fc3908d4-4e50-4041-8d2c-a913b1023335@audiosystemsgroup.com>
> Content-Type: text/plain; charset=UTF-8; format=flowed
>
> On 9/25/2024 8:41 AM, Greg Troxel wrote:
>> A related question is that given a physically small device that plugs
>> in, how are these able to generate common-mode current, given the lack
>> of a counterpoise for an endfed (which is of course not quite endfed,
>> but very off center)?
>
> The antenna, including counterpoise, is all of the wiring to which the
> noise source is connected, like mains wiring, wiring connected to
> whatever the source is connected. The relative field strength will
> depend on the spectrum of what is created inside the device, and the
> radiation efficiency of that random collection of conductors that
> constitute the antenna. :)
>
> Hence my advice when encountering noise is to 1) carefully sniff the
> source and that wiring with a battery operated radio in the frequency
> range of the noise; and 2) start applying chokes to wiring at the source
> until noise is no longer sniffed on nearby wiring. My favorite sniffer
> is a Kenwood TH-F6A talkie with wideband RX. It's not very sensitive,
> but plenty good enough for up-close sniffing. Below 10 Mhz it
> auto-switches to a built-in loop stick, and there's a software switch
> between the loop and the antenna jack.
>
> Inexpensive alternatives sold under the Tecsun brand will get you from
> the AM BC band to 30 MHz and FM broadcast, and one of their higher
> priced models will get you greater sensitivity and the AM aircraft band
> above that. One of those higher priced models (in the $150 range) was
> reviewed by ARRL Labs about 10 years ago.
>
> 73, Jim K9YC
>
>
>
> ------------------------------
>
> Message: 5
> Date: Wed, 25 Sep 2024 12:16:58 -0700
> From: Jim Brown <jim@audiosystemsgroup.com>
> To: rfi@contesting.com
> Subject: Re: [RFI] shielded Ethernet cable, or not
> Message-ID:
> <49161402-691f-41cc-8b87-3e4255c30a19@audiosystemsgroup.com>
> Content-Type: text/plain; charset=UTF-8; format=flowed
>
> Some VERY important concepts, Laws of Physics-related.
>
> A connection to Mother Earth has NOTHING to do with killing noise.
> Quoting the late Neil Muncy, W3WJE, who exposed "The Pin One Problem,"
> as well as serious manufacturing issues with standard audio "rack cable"
> that made them susceptible to RFI, "The Earth is not a sump into which
> noise is poured.
>
> The shield is NOT a "Ground." For shielding to be effective, it must be
> continuous, and connected DIRECTLY to the shielding enclosure at each
> end AT THE POINT OF ENTRY. Failure to do so is "The Pin One Problem,"
> and as Neil predicted to me in bar conversation around 2003, it is the
> primary mechanism coupling RF noise into and out of sources.
>
> My neighbor, N6TV, an IBM retiree who is also a serious contester,
> swears by shielded CAT cable. I've never used it -- but for reasons
> related to lightning protection, I use WiFi in place of wired Ethernet.
> I can do that because I don't need the speed and more stable latency for
> my operation.
>
> A discussion of the issues associated with lightning protection is part
> of this slide deck pdf addressing Grounding and Bonding for hams.
> http://k9yc.com/GroundingAndAudio.pdf Don't let the word "audio" in the
> title throw you -- it's 99% about Lightning Protection and EMC. It
> started out in 2014 for talks I did at Pacificon and Visalia, and was
> updated a few months ago for a talk to the Northern California Contest
> Club. Most of its content was made part of N0AX's ARRL books on the
> topic of Grounding and Bonding, to which I contributed extensively.
>
> 73, Jim K9YC
>
>
> On 9/25/2024 8:29 AM, Greg Troxel wrote:
>> I would like to hear
>>
>> - opinions about the value of shielded vs unshielded Ethernet
>> (assuming chokes held constant).
>>
>> - opinions if sihelded outdoor to non-grounded switch with unshielded
>> back to grounded switch makes sense
>>
>> - experience of anyone who has faced this choice especially their
>> rationale before and their hindsight opinion later
>>
>> - experience of anyone who has done an unshielded to shielded
>> conversion and their hindsight opinion.
>>
>
>
>
>
> ------------------------------
>
> Message: 6
> Date: Wed, 25 Sep 2024 21:34:51 +0000
> From: David Eckhardt <davearea51a@gmail.com>
> To: jim@audiosystemsgroup.com
> Cc: rfi@contesting.com
> Subject: Re: [RFI] wall warts and shielding the DC side - theory?
> Message-ID:
> <CAODdWWFbpxNDLLJkJhqfy2OnSLhKFDeeGqgfBpKDkTNYYkFCnw@mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
>
> Several years ago, maybe a decade ago, I was given three Compaq tower PCs
> to support my radio astronomy interests. I couldn't use them for their
> tremendous generation and radiation of RF energy! However, I "fixed" one
> of them by properly installing a good Corcom line filter right where the
> connection to grid power was provided. Someone in marketing (??) decided
> not to spend the small amount of $$$ to install either a common mode choke
> or the proper line filter. Money talks.
>
> Dave - W?LEV
>
> On Wed, Sep 25, 2024 at 7:04?PM Jim Brown <jim@audiosystemsgroup.com> wrote:
>
>> On 9/25/2024 8:41 AM, Greg Troxel wrote:
>>> A related question is that given a physically small device that plugs
>>> in, how are these able to generate common-mode current, given the lack
>>> of a counterpoise for an endfed (which is of course not quite endfed,
>>> but very off center)?
>>
>> The antenna, including counterpoise, is all of the wiring to which the
>> noise source is connected, like mains wiring, wiring connected to
>> whatever the source is connected. The relative field strength will
>> depend on the spectrum of what is created inside the device, and the
>> radiation efficiency of that random collection of conductors that
>> constitute the antenna. :)
>>
>> Hence my advice when encountering noise is to 1) carefully sniff the
>> source and that wiring with a battery operated radio in the frequency
>> range of the noise; and 2) start applying chokes to wiring at the source
>> until noise is no longer sniffed on nearby wiring. My favorite sniffer
>> is a Kenwood TH-F6A talkie with wideband RX. It's not very sensitive,
>> but plenty good enough for up-close sniffing. Below 10 Mhz it
>> auto-switches to a built-in loop stick, and there's a software switch
>> between the loop and the antenna jack.
>>
>> Inexpensive alternatives sold under the Tecsun brand will get you from
>> the AM BC band to 30 MHz and FM broadcast, and one of their higher
>> priced models will get you greater sensitivity and the AM aircraft band
>> above that. One of those higher priced models (in the $150 range) was
>> reviewed by ARRL Labs about 10 years ago.
>>
>> 73, Jim K9YC
>>
>> _______________________________________________
>> RFI mailing list
>> RFI@contesting.com
>> http://lists.contesting.com/mailman/listinfo/rfi
>>
>
>
> --
>
> *Dave - W?LEV*
>
>
> ------------------------------
>
> Subject: Digest Footer
>
> _______________________________________________
> RFI mailing list
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> http://lists.contesting.com/mailman/listinfo/rfi
>
>
> ------------------------------
>
> End of RFI Digest, Vol 260, Issue 9
> ***********************************
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