[RFI] Bonding to a PC

Sat Mar 9 13:39:46 EST 2019

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 at rogerhalstead.com 
> <mailto:k8ri at 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)