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From: liz@poppyrecords.invalid.invalid (Liz Tuddenham)
Newsgroups: sci.electronics.design
Subject: Re: signal leads that pick up less ambient noise?
Date: Wed, 26 Feb 2025 10:44:16 +0000
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Bill Sloman <bill.sloman@ieee.org> wrote:

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

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.


-- 
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk