The average ham's concept of "ground" is usually completely off the wall
and absolutely incorrect. As Jim stated, "ground" (the Brit's got it
right using the term "earth!) is not a sump/sink for everything bad
associated with RF and/or RFI.
How many time do we hear or read as a "solution" to RF-in-the-Shack:
"Connect a ground"? BS!! What if your "ground" *(earth) conductor is
33-feet to your "ground" (earth) connection? That's a quarter wave on
40-meters, so you have a floating - open circuit - to your "ground" (earth)
connection. Also, its an open circuit at odd harmonics of 7.15 MHz. Do
you have a reliable "ground" (earth) connection? Absolutely not!
In addition, "ground" rods are NOT sufficient for lightning remediation.
They are highly resistive to the preverbial "RF garbage sump/sink" that
most hams believe a single "ground" (earth) rod provides. Further, for
them (notice plural) to remain effective over time, they must be
periodically treated with a solution of CuSO4 (blue vitrol) or NaCl (garden
variety salt).
The absolute most important item to address in lightning remediation is
that everything of concern (electronics) floats up and down in potential
together. That requirement eliminates a "standard practice" of connecting
everything together with copper wire, even of heavy gauge copper wire. When
10-thousands of amperes are encountered from a lightning strike, even
nanoHenries of inductance forms a reflective circuit element! Look at the
feed coax at the very base of any AM BC transmitter. The coax cable is
usually dressed in a large loop before it enter the tower. This loop
introduces enough +jX (inductive reactance) to keep "most" of the
potentially damaging elements of the strike out of the matching network and
transmitter. The requirement I described requires EVERYTHING of concern
sit on a large highly conductive sheet and each piece of equipment of
concern be BONDED to that highly conductive sheet. Doing so results in no
potential differences (high voltages) between the electronics placed and
bonded to that sheet. A connection from that sheet to "ground" (earth)
then bleeds off any charge the sheet may have accumulated.
Thanks, Jim, for motivating me to write this email!🙂😀😉
Dave - WØLEV
On Thu, Jan 23, 2025 at 7:15 PM Jim Brown <jim@audiosystemsgroup.com> wrote:
> On 1/23/2025 4:30 AM, nlsa@nlsa.com wrote:
> > Question: I’ll bet that my noise floor could be improved by a better RF
> connection to Earth, but how can I do it? What mode does EMI take in this
> situation? What is “ground” in a non-metallic enclosure?
> >
> The earth is not a sump into which noise is poured. The ONLY reason for
> an earth connection, and it is ABOUT LIFE OR DEATH, is LIGHTNING
> PROTECTION, and it is required by LAW. So is the bonding of everything.
>
> I would not expect any noise reduction at VHF from an earth connection,
> but proper grounding and bonding is required by Electrical Codes, which
> are LAW, and for human safety.
>
> 73, Jim K9YC
>
>
>
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>
--
*Dave - WØLEV*
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