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Speaking of 'grounds'...




 
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Author Topic: Speaking of 'grounds'...  (Read 124 times)
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wa2tak
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« on: May 26, 2023, 08:28:44 AM »

I'm trying to better understand 'grounds'.

Here's one that perplexes me:

Given a rig that has CHASSIS grounding in the circuitry.

Now, the SIGNAL paths are directly wired to the following stage...that output...and ALL the following stages are also directly wired.

BUT each stage return path is wired to the COMMON CHASSIS.

Question:  why do allllllllllllllllllll those return paths signals...from alllllllll those stages...all jointed together with that 'wired'/chassis GROUNDING getting MIXED TOGETHER...NOT cause havoc???
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KL7OF
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« Reply #1 on: May 26, 2023, 09:45:44 AM »

Electron confusion?  It's FM     Steve
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KD1SH
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« Reply #2 on: May 26, 2023, 09:51:54 AM »

   In a perfect world, ground is alpha and omega - the beginning and the end - nothing can move a properly grounded object above or below earth ground, and anything returned to it no longer exists; it's gone and forgotten. More importantly, it's a common point for all: an oscillator stage, for example, has its cathode referenced to that common chassis, and the buffer stage immediately following it also has its cathode referenced to that same common chassis, and the mixer or multiplier stage after that, and so on, so that there can be no "mixing" going on; there can be no difference in potential between those points. Same for IF cans and the like with a "low side" tied to ground. Once it's ground, it's dead and gone. This is all assuming good continuity; grounds made through screws or whatever, that might come loose or become corroded, can indeed cause chaos.
   But, it gets more complicated when we consider AC safety grounds (that third wire in the power cord) and RF grounds. Assuming no resistance in the ground path, the chassis can never rise above earth ground for low frequency AC or DC, but it's entirely possible to have that same chassis floating all over creation for RF, and even be dangerously "hot" with RF voltage. That can happen when the antenna and feed-line are in such a state that large "common mode" RF currents flow back down the shield of the coax, and the power cord's AC safety ground presents too high an impedance at that frequency to return it all to earth ground. In effect, it's easier to achieve a good ground at DC and low frequency (60 Hz) than it is at RF.

I'm trying to better understand 'grounds'.

Here's one that perplexes me:

Given a rig that has CHASSIS grounding in the circuitry.

Now, the SIGNAL paths are directly wired to the following stage...that output...and ALL the following stages are also directly wired.

BUT each stage return path is wired to the COMMON CHASSIS.

Question:  why do allllllllllllllllllll those return paths signals...from alllllllll those stages...all jointed together with that 'wired'/chassis GROUNDING getting MIXED TOGETHER...NOT cause havoc???

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WBear2GCR
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Brrrr- it's cold in the shack! Fire up the BIG RIG


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« Reply #3 on: May 26, 2023, 10:43:46 AM »

Well, it's not really covered in the texts... but in fact it is all magic!!
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_-_- bear WB2GCR                   http://www.bearlabs.com
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