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From: "Edward Rawde" <invalid@invalid.invalid>
Newsgroups: sci.electronics.design
Subject: Re: signal leads that pick up less ambient noise?
Date: Fri, 21 Feb 2025 11:17:12 -0500
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"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vp95q9$395rh$1@dont-email.me...
> On 21/02/2025 4:07 am, Edward Rawde wrote:
>> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vp6drd$2mqf1$1@dont-email.me...
>>> On 20/02/2025 5:35 am, Christopher Howard wrote:
>>>> Hi, I have a very noisy workbench (lots of digital computers and
>>>> computer monitors nearby) and it seems like I pick up a lot of noise on
>>>> the long leads coming out of the signal generator BNC output - around
>>>> 600 mV p-p. I am wondering if there are any particular leads I could buy
>>>> that would somehow pick up less ambient noise.
>>>
>>> You might think about double shielded coax.The standard woven braid outer offers about 98% shielding and adding a wrap of
>>> aluminised Mylar underneath it get you closer to 100% shielding.
>>>
>>> As other posts have pointed out, your problem is probably going to be earth loops, and wrapping a short length of the coax 
>>> around
>>> a ferrite toroid can help with that. Ralph Morrison wrote the book on the subject back in 1967. I read the first edition back
>>> then, and I've had access to most of the subsequent editions. I've got the fourth edition from 1998 when I finally had to buy my
>>> own copy.
>>>
>>> https://books.google.com.au/books/about/Grounding_and_Shielding_Techniques_in_In.html?id=IxUjAAAAMAAJ&redir_esc=y\
>>
>> The sixth edition (2016) appears to be called
>> Grounding and Shielding: Circuits and Interference.
>> And is not hard to obtain.
>> But unless you want to wade through a book which touches on the calculus of electromagnetic theory (and it's perfectly fine if 
>> you
>> do), you're likely better off focussing on the practical side of things.
>
> Wrong.

Of course Bill. It was predictable that you'd reply like the headmaster.
https://www.youtube.com/watch?v=tYJ5_wqlQPg

I spent perhaps half an hour looking through the book you mentioned (sixth edition).
I can't quite put my finger on why, but I noticed that when talking about skin depth (Page 26, 74 and others) the word "Penetration" 
is used.
This made me wonder how long it might be before I tell you what you can go do with yourself.

> Ralph Morrison's book is sublimely practical; it includes enough electromagnetic theory to let you understand what is going on.
> Cook-book style texts don't, and should be avoided.
>
>> Decades ago before anything like mobile phones existed I worked at a newly constructed facility which had a powerful radio
>> transmitter.
>> The gatehouse was outside the facility and had a PA (Public Address) system installed for communication with people inside the
>> facility.
>> When keying the microphone you could hear nothing inside the facility other than the transmitter modulation.
>> It took many weeks to solve the problem and more than a few people (possibly with PhD level qualifications) demonstrated their 
>> lack
>> of knowledge by proposing solutions such as ferrite toroids in the speaker wiring (100V line system).
>> Eventually the problem was solved as follows.
>> Remove the preamplifier board from the all in one pre amp/power amp unit in the gatehouse.
>> Obtain one metal box of suitable size and drill holes for suitable feedthrough capacitors for all connections.
>> https://www.google.com/search?&q=feedthrough+capacitor&udm=2
>> Mount the board in the box and connect to the feedthrough capacitors as necessary. Close the box.
>> Glue the box to the back of the pre amp/power amp unit.
>> Wire from the feedthrough capacitors to the appropriate points in the unit.
>> The PA was now totally quiet, except for the announcement being made.
>
> Ralph Morrison talks quite a lot about double-screened transformers, which help when where enough current is being injected into 
> the screen on one side to produce the significant voltage drops across the screen.
>
> Powerful radio transmitters do produce quite intense electric fields. You have to put Faraday cages around fluorescent lights to 
> stop them lighting up even when they are switched off.
>
> Back in the days when you'd build a preamplifier board on two layer printed card without any kind of ground plane, you would have 
> had to screen it carefully.
>
> When I was working at Cambridge Instruments a number of old two layer boards were re-worked as four and six layer boards with 
> buried ground planes, and we could leave out the aluminium screening plates we'd had to fit to stop adjacent boards in our racks 
> from messing up their neighbours.
>
>>> The 40kHz periodicity suggests that old cheap switching power supplies are the source of the noise.
>
> -- 
> Bill Sloman, Sydney
>
>