[time-nuts] Re: Death of a Capacitor

[Magnus Danielson]

Hi,

For spikes and RF, common ground is a chimera, a bed-time story for 
kids. The quicker you learn to understand that "ground wire" or "ground 
connection" is just another wire that has resistance, induction, various 
offsets and different noise, the "common" part is very much a "Your 
Mileage May Vary" issue. Concepts to learn is common mode and 
differential mode, and their handling is different. Common mode 
suppression may be useful, or damage your application.

Spikes travels nicely, but local decoupling help to reduce the issue. 
Spikes travels easily through regulators if you have not added 
capacitors to handle it and inductors to object to it. What people do 
not think of is that it's the rise time that defines the path, not the 
frequency. So sharp spikes from 50 Hz may go through, even if 50 Hz as 
frequency is well filtered, but not the spiked signal. Snubbers 
(resistor in series with cap) can help, as it provide a path for the 
spike to go into a resistor.

There is nice books to help with practical engineering on this. Check 
out Ott for instance.

Cheers,
Magnus

On 2021-09-27 00:56, Bob kb8tq wrote:
> Hi
>
> Once you put big inductors in the ground path …. it’s not a common ground anymore.
>
> Bob
>
>> On Sep 26, 2021, at 6:53 PM, Gerhard Hoffmann <ghf at hoffmann-hochfrequenz.de> wrote:
>>
>>
>> Am 27.09.21 um 00:34 schrieb Bob kb8tq:
>>> Hi
>>>
>>> If you start dumping major current spikes into a common ground, it’s amazingly difficult to
>>> get rid of the results.
>> First Principles know the law of the conservation of spikes:
>>
>> Capacitors convert voltage spikes to current spikes.
>>
>> Inductors convert current spikes to voltage spikes.
>>
>> Gerhard
>>
>>
>> (who just has fun with a new  LMX2594 synthesizer board.
>>
>> 10 MHz to 15 GHz, 2 cm**2, 20 dBm, limited amount of empty
>>
>> boards available for free. Soldering them is NOT harmless.)
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