USB Shield grounding


Michael Black <mdblack98@...>
 

Would someone care to test their K3 and see if the USB shield is tied to pin 4 on the USB connector in the K3?  The shield should be tied to chassis.

Also see if the -12V connector is tied to chassis?

The shield should NOT be tied any of the USB pins so it's an easy short test.

I'm on a campaign to get manufacturers to stop tying pin 4 to shield and also stop tying -12V to chassis too.  It's very common and I'm keeping a list on my QRZ page.

Mike W9MDB




ke9uw
 

What does the schematic show?


ke9uw
 

It looks like pin 4 is connected to ground. And shield is connected to ground thru a zero ohm resistor.


Michael Black <mdblack98@...>
 

The USB shield on most every piece of equipment is tied to the chassis.  This two-sided grounding is more then unnecessary.  In addition many tie pin 4 on the USB to shield too....shame...

I'm getting ready to make a USB cable with the adaptors listed on my QRZ website plus a breakout USB adaptor.  So it will break the shield on both ends of the cable and I can tie the shield to ground on just one end like it should be to my common ground point.

In addition...lots of equipment ties the DC common terminal to the chassis too...yuck....
Depending on the equipment you may be able to break that ground inside the chassis if they just run a wire from the DC common to chassis.  But all the equipment I've seen also ties the internal circuitry to chassis at multiple points (yuck again) and most all through the circuit card mounting screws too.  

The ground diagram is almost impossible to draw there are so many points.

Mike W9MDB

On Saturday, May 7, 2022, 11:04:39 AM CDT, Bob McGraw - K4TAX <rmcgraw@...> wrote:





Are you saying the shield is connected to the ground terminal, which may or may not be chassis or the -12V point?  

73
Bob, K4TAX


Joe Subich, W4TV
 

You are spitting into the wind.

It was easy to separate signal return and shield on cables
when every connector was bolted to a metal panel and the
connections were point to point. Not so easy when cases
are primarily plastic, connectors mounted to circuit boards
and float through holes in the case and power/signal shares
a common circuit board ground.

Similarly separating the power return was easy when every
piece of equipment had a transformer isolated power supply
with one side of the primary going to the line and the other
side to neutral (the line cord). Again, that's not so simple
with DC powered equipment where the negative/ground DC rail
and signal common share a common ground plane on a circuit
board.

What you are really after would double or treble the cost of
production of electronic equipment. You would need: 1) solid
metal enclosures, 2) all connectors bolted to the case, 3)
all connectors connected to the circuit board via cables
and connectors, 4) multi-layer circuit boards with separate
ground planes for DC and signal common.

As soon as you mount a USB connector, shielded Ethernet
connector, serial connector, audio in/audio out connectors,
headphone connectors, etc. directly to the circuit board
and poke them through the case without bolting their frame
or shell to the case, you have created a "pin 1" problem.

73,

... Joe, W4TV

On 2022-05-07 4:46 PM, Michael Black via groups.io wrote:
The USB shield on most every piece of equipment is tied to the chassis.  This two-sided grounding is more then unnecessary.  In addition many tie pin 4 on the USB to shield too....shame...
I'm getting ready to make a USB cable with the adaptors listed on my QRZ website plus a breakout USB adaptor.  So it will break the shield on both ends of the cable and I can tie the shield to ground on just one end like it should be to my common ground point.
In addition...lots of equipment ties the DC common terminal to the chassis too...yuck....
Depending on the equipment you may be able to break that ground inside the chassis if they just run a wire from the DC common to chassis.  But all the equipment I've seen also ties the internal circuitry to chassis at multiple points (yuck again) and most all through the circuit card mounting screws too.
The ground diagram is almost impossible to draw there are so many points.
Mike W9MDB
On Saturday, May 7, 2022, 11:04:39 AM CDT, Bob McGraw - K4TAX <rmcgraw@...> wrote:
Are you saying the shield is connected to the ground terminal, which may or may not be chassis or the -12V point?
73
Bob, K4TAX


Michael Black <mdblack98@...>
 

Tis' a bit of a Don Quixote windmill problem....but we can hope.  Elecraft has been particularly responsive to such problems.

Mike W9MDB

On Saturday, May 7, 2022, 04:14:31 PM CDT, Joe Subich, W4TV <lists@...> wrote:






You are spitting into the wind.

It was easy to separate signal return and shield on cables
when every connector was bolted to a metal panel and the
connections were point to point.  Not so easy when cases
are primarily plastic, connectors mounted to circuit boards
and float through holes in the case and power/signal shares
a common circuit board ground.

Similarly separating the power return was easy when every
piece of equipment had a transformer isolated power supply
with one side of the primary going to the line and the other
side to neutral (the line cord).  Again, that's not so simple
with DC powered equipment where the negative/ground DC rail
and signal common share a common ground plane on a circuit
board.

What you are really after would double or treble the cost of
production of electronic equipment.  You would need: 1) solid
metal enclosures, 2) all connectors bolted to the case, 3)
all connectors connected to the circuit board via cables
and connectors, 4) multi-layer circuit boards with separate
ground planes for DC and signal common.

As soon as you mount a USB connector, shielded Ethernet
connector, serial connector, audio in/audio out connectors,
headphone connectors, etc. directly to the circuit board
and poke them through the case without bolting their frame
or shell to the case, you have created a "pin 1" problem.

73,

    ... Joe, W4TV


On 2022-05-07 4:46 PM, Michael Black via groups.io wrote:
The USB shield on most every piece of equipment is tied to the chassis.  This two-sided grounding is more then unnecessary.  In addition many tie pin 4 on the USB to shield too....shame...

I'm getting ready to make a USB cable with the adaptors listed on my QRZ website plus a breakout USB adaptor.  So it will break the shield on both ends of the cable and I can tie the shield to ground on just one end like it should be to my common ground point.

In addition...lots of equipment ties the DC common terminal to the chassis too...yuck....
Depending on the equipment you may be able to break that ground inside the chassis if they just run a wire from the DC common to chassis.  But all the equipment I've seen also ties the internal circuitry to chassis at multiple points (yuck again) and most all through the circuit card mounting screws too.

The ground diagram is almost impossible to draw there are so many points.

Mike W9MDB










On Saturday, May 7, 2022, 11:04:39 AM CDT, Bob McGraw - K4TAX <rmcgraw@...> wrote:





Are you saying the shield is connected to the ground terminal, which may or may not be chassis or the -12V point?

73
Bob, K4TAX