[Elecraft] K3: Added protection for RS-232 port (summary)

[Tom W8JI]

> IN addition to bonding my radio ground rod to the electrical ground
> (on the other side of the house), I will have my radio ground going
> to my cable entrance plate.  From there I have two tables and my
> racks arranged in an U configuration with radio table facing the
> racks six feet across the operating space.  How should I run
> grounds?  My intention was to run a separate ground wire to a ground
> buss on the radio table an another one to the racks both tied to the
> copper bolt holding the outside ground wire.

All cables including power should come from the entrance panel ground to the 
desk. That should be the common ground point. The ground should come from 
the entrance panel to the desk with the wires and cables that are bundled or 
close spaced and parallel from the entrance point to the desk.

> The only dc-isolated wiring in my shack is the soundcard audio lines
> from radios to computers.  Everything powered with ac is tied to the
> safety 3rd wire in the house wiring.  -HV thru a 100-ohm/25w resistor
> , -24vdc, and -12vdc are all strapped to ground.  All coax lines
> exiting the room are grounded at the entrance plate.
> See any problems with this?

A 100 ohm 25 watt resistor is not a safe negative rail ground in a power 
supply.
I see it in Handbooks, but whoever came up with that as a safety system 
should be severely beaten!

Even with a 10 ohm clamp resistor, a B+ fault could pull a negative 
interconnect up to a few thousand volts above chassis. Capacitors can dump 
hundreds of amps while they discharge. Get some big diodes on that line on 
both ends and have a big chassis-to-chassis strap independent of the 
negative lead (interlocked if you can manage). A 100 ohm negative rail 
safety is like no safety clamp at all. Normal plate currents could produce 
lethal voltages, and a fault could drive the negative interconnect up to 
thousands of volts negative as capacitors discharge.

73 Tom