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Author Topic: Speaking of 'grounds'...  (Read 2155 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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"Gosh, Batman, I never knew there were no punctuation marks in alphabet soup!"
—Robin, in the 1960's Batman TV series.
WBear2GCR
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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
K9MB
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« Reply #4 on: June 01, 2023, 09:42:16 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???


Agreed- I did a study of this a while back when I was installing ground rods at antennas and outside the shack.
The common idea is about inductance and rise time.
In transient analysis of an inductor, a very high rise time causes a massive spike to be generated and if a very large spike is transfrred into the power line from lightning, even at some distance, the common ground on the power line can rise hundreds or thousands of volts in very short duration spikes.
It is essentially impossible to make a perfect groumd to sink or source electrons instantaneously, the way we protect equipment is to tie the common of tje power lime to a common place. This is called bonding.
Now, when a spike comes in, the hot goes up and the common goes up, but at the same time, so that the difference- seen by our equipment stays in a safe region to eliminate or limit damage. This will not save you from a direct hit. For that, you must disconnect all equipment and put it in a Faraday cage. We seldom do that unless we are away for a time.
If you think that you can put in multiple ground rods and not bond it all to the service entrance, you may be disappointed. No matter how big your ground strap, it will have some inductance and be vulnerable to inductive spikes. Common bonding at a single point puts your equipment in an isolated universe with the maelstrom in the outer darkness.
The comments about high frequencies is the same thing, but the signal now has high rise time and ground loops form and chaos arises in ways we can only appreciate by ignoring good practice. Anyone who has designed VHF and UHF amps understands ground loops as well as their gray hair…😉
The ARRL book Grounding and Bonding is a good place to start. A lot is in your Google Search. 73, Mike


PS: Jim Brown has great information on grounding as well as rf choke design.

http://www.audiosystemsgroup.com/K9YC/K9YC-old.htm
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K1JJ
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« Reply #5 on: June 01, 2023, 11:46:15 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???



IE, why don't the electrons bump into each other?    I remember that same question with telecopes.... why didn't the photons of the main mirror of a Dobsonian reflector bump into the photons of the secondary mirror and causes distortions?   (tertiary mirror)   After all, the secondary light on its way to the eyepiece travels directly across the main light path.

The answer is that there are HUGE distances between electrons or photons, something like astronomical relative distances.  And, it doesn't take a lot of electrons (having mass) to create HUGE power as based on the E=MC2 formula.   Something like when two galaxies pass thru each other.  Gravity has a big effect (energy) but the stars are so far apart compared to individual size, they rarely collide.  For example, our sun is just about 5 light seconds in diameter but 4 light years from the nearest other star.  

If the sun were the size of a football field, then Proxima Centuri would be another football field about 35,000 miles away.  Lots of empty space out there, including at the atomic level.

At least that's my seat of the pants take on it.... :-)

T
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KD1SH
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« Reply #6 on: June 02, 2023, 11:19:31 AM »

   All this gets even more interesting when one looks at some of the assumptions made by earlier pioneers in the field of alternating currents in wires. Oliver Heaviside - the scientist who solved the problem of reactance setting a limit on the speed at which telegraphy, or voice, could be sent over wires - came to the conclusion that most of the alternating energy didn't actually travel "through" a wire, but rather the wire simply acted as a "guide", with the actual energy being contained in the magnetic field which appeared at right angles to the wire. Being at right angles to the wire, the magnetic field was obliged to enter the wire starting at the surface and then working its way inward, but the faster the field alternated the less time it had to move toward the center of the wire before it changed direction and had to start all over again; hence the "skin-effect." This, for Heaviside, was easily reconciled with Maxwell's work, which of course has survived the test of time.
  Later came the discovery of the electron and our modern definition of current flow; thus our current (no pun intended) assumption that the skin effect is due to magnetic eddy currents, which create a stronger counter-emf in the center of the conductor than toward the outer surface.
 
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"Gosh, Batman, I never knew there were no punctuation marks in alphabet soup!"
—Robin, in the 1960's Batman TV series.
wa2tak
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« Reply #7 on: June 02, 2023, 11:37:38 AM »

Here's a MOST interesting 'ground' case!
I'm restoring a Heathkit HW-32A..20 meter transceiver...from a SK estate.

With the radio in receive...I was checking circuit voltages.
Had the antenna plugged in.

Dig this...I got a station just above the noise level.
When I clipped the GROUND LEAD from the B&K Digital Multimeter to the chassis...
...the station went READABLE!!

I then grounded the radio chassis to the CASE of my URM-25F signal generator...station was again readable...took of the ground...he went back to noise level.

LESSON:
The 3-prong AC plug 'ground' of either unit affected the 32A received signal level...noticeably!!

The Heathkit HP-23A power supply has only a 2-prong AC plug.
( it has one of those 2 fuse holders built in...during this 'venture' BLEW UP the power supply...had to 're-do' it...the darn gent-previous owner had 10 AMP FUSES...in place of the 3 amp )

Yup...got to 3-wire the AC on it.
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KD1SH
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« Reply #8 on: June 02, 2023, 12:10:40 PM »

On your B&K Digital Multimeter, do you mean the (-) banana jack, which would be the black one, or a special terminal marked "ground"? I'm not familiar with your B&K meter, but all of my AC powered bench multimeters have both of their inputs, (-) and (+), isolated from ground.
If your B&K meter does indeed have its (-) terminal tied to your AC receptacle ground, be very careful! Just as with an oscilloscope, any part of a circuit that you touch that negative probe to gets shorted to ground.
It's unusual for a digital multimeter to have a grounded (-) jack; more than likely your receive picked up because your probe provided a bit of a counterpoise to an otherwise ungrounded receiver.

Here's a MOST interesting 'ground' case!
I'm restoring a Heathkit HW-32A..20 meter transceiver...from a SK estate.

With the radio in receive...I was checking circuit voltages.
Had the antenna plugged in.

Dig this...I got a station just above the noise level.
When I clipped the GROUND LEAD from the B&K Digital Multimeter to the chassis...
...the station went READABLE!!

I then grounded the radio chassis to the CASE of my URM-25F signal generator...station was again readable...took of the ground...he went back to noise level.

LESSON:
The 3-prong AC plug 'ground' of either unit affected the 32A received signal level...noticeably!!

The Heathkit HP-23A power supply has only a 2-prong AC plug.
( it has one of those 2 fuse holders built in...during this 'venture' BLEW UP the power supply...had to 're-do' it...the darn gent-previous owner had 10 AMP FUSES...in place of the 3 amp )

Yup...got to 3-wire the AC on it.
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"Gosh, Batman, I never knew there were no punctuation marks in alphabet soup!"
—Robin, in the 1960's Batman TV series.
wa2tak
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« Reply #9 on: June 02, 2023, 12:34:09 PM »

Unit is B&K 2831A
Please see attachments.


* B&K 2831a leads.JPG (288.39 KB, 1600x1200 - viewed 101 times.)
* Schematic test leads.doc (213 KB - downloaded 55 times.)
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KD1SH
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« Reply #10 on: June 02, 2023, 01:07:03 PM »

In my view, the labeling shown on your meter indicates not that the black terminal is ground, but that the highest potential you can put on that terminal with reference to ground is 500V. On the schematic, it shows that the "common" terminal is grounded, but note that the ground symbol used isn't the commonly used symbol for either chassis or earth ground, but rather the standard symbol for "digital" or "signal" ground, which is simply a common ground for signals but not a "real" ground tied into the AC supply. When you connected that "common" jack to your receiver, your receive probably improved simply because the length of the probe wire acted as a counterpoise.

Unit is B&K 2831A
Please see attachments.
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"Gosh, Batman, I never knew there were no punctuation marks in alphabet soup!"
—Robin, in the 1960's Batman TV series.
wa2tak
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« Reply #11 on: June 02, 2023, 03:02:37 PM »

I also used the alligator-clip wire to the chassis by itself...no 'improvement'...
And...when chassis-connected to the meter and the signal gen case..I removed their AC plug...radio signal went down.
When they were in the AC outlet...tapped the chassis connection..."good"..'no good'...good..no good.
Don't think I was an 'antenna' as the leads were insulated from my hand.
Had good signal when not touching also.
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KD1SH
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« Reply #12 on: June 02, 2023, 03:15:45 PM »

Fun stuff. Well, what is a ground for low frequency AC isn't necessarily a ground for RF, and vice-versa. Those common "signal" grounds in your meter might very well be isolated from earth ground, but for RF, not so much. Sometimes, like Bear said, it's magic.

I also used the alligator-clip wire to the chassis by itself...no 'improvement'...
And...when chassis-connected to the meter and the signal gen case..I removed their AC plug...radio signal went down.
When they were in the AC outlet...tapped the chassis connection..."good"..'no good'...good..no good.
Don't think I was an 'antenna' as the leads were insulated from my hand.
Had good signal when not touching also.
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"Gosh, Batman, I never knew there were no punctuation marks in alphabet soup!"
—Robin, in the 1960's Batman TV series.
W3SLK
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« Reply #13 on: June 02, 2023, 05:07:51 PM »

K1JJ said:
Quote
IE, why don't the electrons bump into each other?    I remember that same question with telecopes.... why didn't the photons of the main mirror of a Dobsonian reflector bump into the photons of the secondary mirror and causes distortions?   (tertiary mirror)   After all, the secondary light on its way to the eyepiece travels directly across the main light path.

The answer is that there are HUGE distances between electrons or photons, something like astronomical relative distances.  And, it doesn't take a lot of electrons (having mass) to create HUGE power as based on the E=MC2 formula.   Something like when two galaxies pass thru each other.  Gravity has a big effect (energy) but the stars are so far apart compared to individual size, they rarely collide.  For example, our sun is just about 5 light seconds in diameter but 4 light years from the nearest other star. 

If the sun were the size of a football field, then Proxima Centuri would be another football field about 35,000 miles away.  Lots of empty space out there, including at the atomic level.

At least that's my seat of the pants take on it.... :-)

I'll remember that when the Andromeda Galaxy and our Milky Way Galaxy collide with each other in about 4.5 billion  years.
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Invisible airwaves crackle with life, bright antenna bristle with the energy. Emotional feedback, on timeless wavelength, bearing a gift beyond lights, almost free.... Spirit of Radio/Rush
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