Re: signal leads that pick up less ambient noise?

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 paragraph on page 65.
The fifth edition does not mention them at all as 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. Later editions did move on to higher frequency applications.
I never used a feed-though capacitor anywhere in  the work I did - if we need to put a fast signal through a conducting bulk-head we used coax feed-throughs. Feedthrough capacitors are relatively exotic devices.
Your example of their application seems to be a case where an RF specialist went in for a bit of over-kill.
--
Bill Sloman, Sydney