Re: signal leads that pick up less ambient noise?

"Liz Tuddenham" <liz@poppyrecords.invalid.invalid> wrote in message news:1r8cyx3.z5ufvcaq14qsN%liz@poppyrecords.invalid.invalid...

Bill Sloman <bill.sloman@ieee.org> wrote:
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On 26/02/2025 4:55 pm, Edward Rawde wrote:

"Bill Sloman" <bill.sloman@ieee.org> wrote in message
news:vpm0qm$29gbe$1@dont-email.me... > On 26/02/2025 4:39 am, Christopher
Howard wrote: >> Bill Sloman <bill.sloman@ieee.org> writes: >>

On 25/02/2025 4:46 am, Christopher Howard wrote: >> Google for
coaxial feed through capacitors. Capacitors and resistors don't ring.
Adding inductance can introduce ringing. but enough resistance can
make the resonant circuit critically damped and the voltages and
current will decay monotonically.

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So, when you use a coaxial feed through capacitors on your Faraday
cage, do you add a resistor right after the capacitor, to
reduce/eliminate ringing?

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The whole point about coaxial connectors is that the distributed
capacitance and inductance gives you a R50R transmission line. The only
way to get "ringing" out of that is to fail to terminate the
transmission line with  it's characteristic impedance. In practice it
is hard to do it perfectly and you do tend to get low level
reflections, but they die out fast,
>

Or are you just trying that all your inputs on the board have
resistors before whatever op amps or other components that they feed
into?

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The message is rather more complicated than that. The later editions of
Ralph Morrison's book do go into that in more detail than the earlier
editions.

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The sixth edition only mentions the "feed-through" capacitor in one
The paragraph on page 65. fifth edition does not mention them at all as
The far as I can tell.

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Feed-through capacitors seem only to be used in RF electronics, and
Ralph Morrison's book initially concentrated on regular industrial
electronics.

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Industrial electronics may not contain RF devices but they are more and
more likely to be exposed to strong RF fields from external sources such
as mobile 'phones.  Putting critical circuits inside metal boxes with
filters on the incoming wires is much more prevalent now than it was a
few years ago - the circuits haven't changed but the hostile environment
has.
>
Relays and cam timers may be set to make a comeback.

In the OP's case filtered connectors may be overkill and too expensive but it is worth knowing about them.
https://www.google.com/search?&q=filtered+connectors&udm=2
And there are some cheaper ones.

Anyone designing medical devices these days should be sure to take account of the effect of a mobile phone an inch away.
After all it's no longer possible to keep mobile phones out of hospitals or out of anywhere at all unless you want to search
everyone on entry.

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--
~ Liz Tuddenham ~
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