Typically, IF a computer generates RFI, the three most likely sources
are the power supply, network interface connector cards (NIC) and a lack
of ground.
As Jim Brown said, there is no such thing as a ground loop.
Many consumer computers cut corners where ever they can save a nickle,
or dime and cheap power supplies seem to be a common source, or target.
These are switching power supplies that may generate massive RFI. The
cases of these are simple, interlocking, soft, bare Aluminum panels. No
screws, just tabs stuck through matching slots and twisted (and easily
broken if disassembled). The hash generated may propagate down the power
cord
The green wire is supposed to connect to the shielding, or at least to
the power supply. Some don't connect to anything. In many older, or
today's inexpensive offerings there is NO shielding except the metal box
containing the power supply. There have already been suggestions
addressing this. Read Jim Brown's tutorial. It a source of good
educational material.
Then there is the NIC. It's likely a plug in board, but nay be integral
with the motherboard. We are dealing with super high frequencies (as
high as 4 or 5 GHz) here so a short wire can serve as an antenna.
These are available for as little as $12, or less, or quite a bit more.
It's a case of you get what you pay for (USUALLY), but you can pay far
more than needed.
I had an "all-in-one" motherboard that had the resident NIC taken out by
lightning. I have quite a few plug in NIC boards. I plugged on in and
it worked fine with no noise from the fried section.
BTW, the unterminated shield on some cables instead of doing nothing may
actually serve as an unwanted antenna for network signals, or power
supply hash, making it far worse than doing nothing.
73, Roger (K8RI)
On 3/1/2019 10:10 PM, Sean Waite wrote:
That does raise a question. If the chassis of the computer is bonded
to the electrical ground as well as the station ground bus, does that
increase your chances of ground loops or potential increased noise
from dirt on your house power circuit? I have my PC bonded via bolt
through one of the van vents on the chassis. If it's doing much I
can't tell, there's so much else going on at my house that my noise
floor is pretty high anyway.
73,
Sean WA1TE
On Fri, Mar 1, 2019 at 8:27 PM Roger (K8RI) <k8ri@rogerhalstead.com
<mailto:k8ri@rogerhalstead.com>> wrote:
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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--
Sent from my Motorola DynaTAC 8000X
--
Roger (K8RI)
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