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Author Topic: Weird grounding issue...  (Read 655 times)

W9WQA

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Re: Weird grounding issue...
« Reply #15 on: January 31, 2023, 07:28:32 PM »

draw a wire diagram, so simple... ac leakage can make radio hot/ dangerous without the ground.

some just cant see this...???toooo simple
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KD6VXI

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Re: Weird grounding issue...
« Reply #16 on: February 01, 2023, 02:52:12 AM »

So, what is the question? Of course, it stays on. It is a problem only ham radio operators suffer from, and the problem is in your DC power supply and using a radio designed for a car in your house.

The problem lies in your DC power Supply, your Astron. It is outdate still using 1960's grounding topology. Your DC Negative output terminal is bonded to the chassis of the DC power supply. That does two nasty thing hams love because it gives them problems to fix.

First, you lose AC and DC electrical isolation required by all electrical codes placing your radio in a nasty daisy-chained ground loop. Now any noise flowing in the AC ground system is now flowing through your DC ground system (your radio). The two mix together, have an orgy, and produce noise. One big party with both the front and back doors wide open for anything to come inside and look around. You're in a Ground Loop!

The second thing it does is it turns your whole ground system into a DC negative circuit conductor. You no longer have a ground. Your car radio power and ground topology are two-wire vs modern 3-wire systems. Inside your radio, the DC negative is bonded to the chassis of the radio. A huge no-no in the modern world. Compounding the problem is your DC power supply with the chassis bonded to DC Negative again. This places Ground in parallel with your DC negative return conductor. By doing that, you no longer have Ground, you have a DC circuit conductor you call Ground.

So, when you lift the DC wire from you power supply, your coax shield and station ground are there to take up the slack Stupid simple to fix, so simple most hams have not figured it out in 50 years when the electrical world changed and went to 3-wire topology. Open that antiquated Astron and remove the jumper that bonds DC negative output terminal to the Chassis. Do that and all the problems go away. Problem is, it can eliminate a lot of noise problems you guys like to waste a lot of money and time fixing with band aids rather than addressing the real problem. Gives you something to do, I guess.

Astron makes batteries?

OP explicitly stated he is powering his station from a battery.

And the answer is MUCH more likely that the radio has the chassis bonded to ground.  Like every single 2SC2879 having radio has had that doesn't have a floating heat sink.

The emitter of the final output transistors is bonded to the case of the transistor.  The emitter also has the ground lead attached to it.

As such, the chassis of the radio IS at negative DC potential.

What's funny is, CB radios typically have floating systems.  Almost every single 100 watt or better ham radio produced in the last 30 years DOESN'T.....  Even if you isolate the DC ground from the safety ground in the power supply it isn't going to make a difference because as soon as you hook up anything with a bipolar transistor in it with the emitter bonded to the case, you lose your DC and safety ground isolation.

Argue all you want about the rest, you aren't going to fix that problem without redesigning at least thermally, the radio(s) in question.

--Shane
WP2ASS / ex KD6VXI
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KT0DD

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Re: Weird grounding issue...
« Reply #17 on: February 02, 2023, 04:24:11 PM »

Well, I'm not going to worry about it. I'm not getting any kind of distortion, RF feedback or artifacts on my TX signal and RX seems just fine. I'll just have to be careful working on this equipment and disconnect everything from the battery completely and from each other if I work on anything. Nice thing is I no longer (Ok, RARELY and it has to be something simple) do any of my own work as I'm too shaky to solder Hi Hi. Thanks for all the info. 73.

Todd - KT0DD
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W9WQA

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Re: Weird grounding issue...
« Reply #18 on: February 02, 2023, 10:00:00 PM »

the reason for the jumper is to be sure the fuse blows if/when there is a short or leakage.
otherwise you can have ac line volts on the radio/ ant....its too simple
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W9IQ

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Re: Weird grounding issue...
« Reply #19 on: February 03, 2023, 02:10:34 AM »

the reason for the jumper is to be sure the fuse blows if/when there is a short or leakage.
otherwise you can have ac line volts on the radio/ ant....its too simple

I understand your point but a properly made transformer makes this a non-issue by UL standards. The metal chassis should be connected to the safety ground but the DC minus can be isolated.

The same concept applies to switching power supplies. The high frequency transformers can provide sufficient isolation for safety purposes.

- Glenn W9IQ
« Last Edit: February 03, 2023, 02:19:47 AM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W9WQA

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Re: Weird grounding issue...
« Reply #20 on: February 03, 2023, 05:47:09 AM »

the reason for the jumper is to be sure the fuse blows if/when there is a short or leakage.
otherwise you can have ac line volts on the radio/ ant....its too simple

I understand your point but a properly made transformer makes this a non-issue by UL standards. The metal chassis should be connected to the safety ground but the DC minus can be isolated.

The same concept applies to switching power supplies. The high frequency transformers can provide sufficient isolation for safety purposes.

- Glenn W9IQ

 can be isolated.
can provide sufficient isolation
 properly made transformer
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KC6RWI

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Re: Weird grounding issue...
« Reply #21 on: February 03, 2023, 07:52:07 AM »

I've seen plenty of transformers , failed ones to. I'd say that most of the time the failure is between the wires of the primary with that thin varnish coat. The core of the transformer is further insulated with additional paper or card type paper, that would seem even harder to make some ac make it thru to the core. I think the user would be smelling some burnt smell before that happened.
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KT0DD

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Re: Weird grounding issue...
« Reply #22 on: February 04, 2023, 11:03:41 AM »

Forgot to mention, I'm running the factory power cord with fuses on both + & - leads. I'm making sure the negative stays connected to the battery, I'm not trying to short-cut (pun intended) anything. 73 and Thank you for the constructive comments.

Todd - KT0DD
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W9WQA

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Re: Weird grounding issue...
« Reply #23 on: February 04, 2023, 05:41:07 PM »

I've seen plenty of transformers , failed ones to. I'd say that most of the time the failure is between the wires of the primary with that thin varnish coat. The core of the transformer is further insulated with additional paper or card type paper, that would seem even harder to make some ac make it thru to the core. I think the user would be smelling some burnt smell before that happened.

sounds good,  until you THINK,,,
THE CORE IS GROUNDED IRON,,,that blows the fuse as you want.
leakage from primary to secondary winding is the problem,,,but that will never happen !!! in a properly designed transformer,,,or parachute !!
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WA8NVW

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Re: Weird grounding issue...
« Reply #24 on: February 06, 2023, 03:00:57 PM »

sounds good, until you THINK,,,THE CORE IS GROUNDED IRON,,,that blows the fuse as you want. 
leakage from primary to secondary winding is the problem,,,but that will never happen !!! in a properly designed transformer,,,or parachute !!

All it takes is a lightning hit on the overhead power lines in your neighborhood.  Then  you've got Ltning HI on the service phase conductor, Ltning LO (ground) on the neutral of the ljne cord.and lots of inductance to make L di/dt.  I don't recall the exact insulation standoff value that UL requires for the varnish winding layer, but the number 1 kV keeps jumping into my brain, so if the lightning strike potential exceeds 1 kV it can arc through the varnish and paper wrap.  Now if you calculate the induced L di/dt voltage appearing across 25 feet of #6 ground conductor, it comes out to just over 18 kVAC.  It's more than twice that for a typical 6 ft  #16 ga line cord.
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W9IQ

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Re: Weird grounding issue...
« Reply #25 on: February 06, 2023, 03:34:22 PM »

If the core is grounded and the chassis is grounded then what you describe will have no effect on the secondary output.

UL has this very well thought out...

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W9WQA

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  • Posts: 990
Re: Weird grounding issue...
« Reply #26 on: February 06, 2023, 04:43:17 PM »

If the core is grounded and the chassis is grounded then what you describe will have no effect on the secondary output.

UL has this very well thought out...

- Glenn W9IQ

tell us once more,,,

"you cant have leakage from pri to sec"..???
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