[Elecraft] VK9MT transmit audio distortion.

[Joe Subich, W4TV]

 > Also, any time storms approach, I pull the USB ports.  They
 > seem to be sensitive to such damage.

They would not be if you include the computer in the "short, fat"
ground bus.  The problem is that many computers do not provide
a reasonable ground connection ... the only "ground" is via the
power supply return to the third wire of the power cord (if it
even exists).  Many amateurs do not properly bond their tower and
RF ground to the power line entry ground (as required by NEC)
which allows the computer and rig to float separately in event
of a storm.

All it takes is for the rig/interface to go more that 7 or 8 volts
more positive than the computer or more than about 0.5V more negative
than the computer and the USB interface is over or reverse voltage
and "poof" goes the USB port.  Better devices now contain external
"protectors" - diodes that clamp the power supply and data lines
relative to circuit common but they still have limited capacity in
event of a strong, nearby lightning strike.

While the USB or serial port (particularly "low power" serial ports
designed with 3.3 or 5V logic) may be especially sensitive to the
"separate ground" issue, failing to bond the tower/RF ground to the
power line entrance is a significant issue of safety for your house
and *all* devices connected to the power distribution system.  With
separate grounds, a direct strike can force several *thousand* amps
between the two grounds via the "safety" ground (third wire)
connection.  The result can be massive damage to appliances and even
serious house fire.

73,

    ... Joe, W4TV


On 4/7/2014 2:58 PM, AG0N-3055 wrote:
>
>> So short chassis-to-chassis bonding combined with a bond from
>> one of those chassis to the common point is the safest from a lightning
>> safety point of view, because it
>> minimizes the loop area.
>
> You've got a good point, Jim.  However, I would prefer a combination of
> both methods.  I'd run a (good low reactance) buss, AND another to the
> grounding point from each buss attachment point on each unit.  Your
> point about all of the ins and outs on this stuff leaves plenty of room
> for loops.  Also, any time storms approach, I pull the USB ports.  They
> seem to be sensitive to such damage.
>
> Gary
>