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Re: [RFI] Bonding to a PC

To: Sean Waite <waisean@gmail.com>
Subject: Re: [RFI] Bonding to a PC
From: "Roger (K8RI)" <k8ri@rogerhalstead.com>
Date: Sat, 9 Mar 2019 13:39:46 -0500
List-post: <mailto:rfi@contesting.com>
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.

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
    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
    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
    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
    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
    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
    I could stand on any of mine. They are strong, but they are also
    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
    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
    at least three additional routes for lightning into the station. 
    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
    already posted

    I doubt many build their own computers, but now days it has become
    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
    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
    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
    > 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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