[RFI] Bonding to a PC

Roger (K8RI) k8ri at rogerhalstead.com
Fri Mar 1 20:27:04 EST 2019

Bonding to a computer?
There have been many a tale of RFI from computers and no few of station 
RF getting into the computer.

A GOOD computer will not generate RFI!

HOWEVER there are many big name brands that do. Price and brand name are 
no guarantee you'll get a good computer.
Bonding for safety is a good idea.  You can't always keep lightning out, 
but if all lines in and out rise even to thousands of volts at the same 
time it's unlikely any damage will occur.

Computers are a commodity and if a dime can be saved here and there, 
it'll soon add up to hundreds of thousands of dollars...or more
If I were to undergo a project like this, I'd pick the band, or bands, 
with the most interference and use that as a base , or starting line, 
but don't neglect the other bands and after adding a device to the 
bonding, check for any change from, or to  the computers.

NOTE: The green wire in your electrical wiring and in the power cord 
should be bonded to the power supply enclosure. They aren't always.

Consumer grade computers/PCs tend to have plastic cases (IE: No 
shielding) and inexpensive power supplies ($10 - $15 range) in stamped 
Aluminum cases with little or no RFI suppression. If accessible I'd 
ground directly to the Al sub chassis. The Serial and USB ports do have 
a ground although tiny.  I'd not depend on a ground through #22 or 
smaller wire.

Custom built and gaming computers tend to have metal cases such as 
small, mid, and full size tower cases, typically made of steel. At 180#, 
I could stand on any of mine. They are strong, but they are also large 
and heavy and not inexpensive.  The power supplies may run as much as 
1200 Watts. I use 850 W supplies that even have power factor correction 
built in and generate no RFI.   BUT computers often connect to phone 
lines and the station. Add to that the AC line and the network you have 
at least three additional routes for lightning into the station.  Good 
power supplies run from around a $100 to well over $300

I haven't read the entire thread so I apologize if I'm repeating things 
already posted

I doubt many build their own computers, but now days it has become quite 
simple, at least for the mechanically inclined.  They are modular and 
relatively simple to plug together, But RTFM as there are things like 
the motherboard, CPU, and memory that must be compatible.  The underside 
of the CPU is a mass of tiny, fragile, pins and no place for heavy 
hands. Install with care.  There is a tiny mark on the CPU and a 
corresponding mark on the socket for alignment. It should drop right in. 
If any force is needed, you have a problem.

73, Roger (K8RI)

BTW, many (certainly not all) new computers now include a serial port. 
Often there is a small socket on the motherboard.  In that case you have 
to purchase a small adapter plate that has the serial port and a plug to 
fit the motherboard

On 2/28/2019 2:34 PM, N4ZR wrote:
> I want to try to manage RFI in my shack, among other things, by 
> bonding all chassis together, including my shack computer, but the 
> question has come up - where can I find chassis ground on a PC without 
> serial or parallel ports?  Is there a design standard, such as 
> connecting the power supply chassis to ground buses on the 
> motherboard, that makes this easy or does it have to be figured out PC 
> by PC?

Roger (K8RI)

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