So long as you have properly decoupled any and all conductors entering and
leaving your enclosures, I believe you are fine for radiated fields from
close-by strikes. Direct strikes? No.
The devil is in the details of how well you decouple other conductors that
enter/leave your "mostly" shielded enclosures. Remember, the best way to
violate a good Faraday cage - and I see this ALL THE TIME(!!!!) with newbie
and some oldie designs - is to poke an non-decoupled conductor into the
cage. I have a demo using a live animal trap and a battery powered crystal
oscillator which I place inside the trap that can convince anyone of that
absolutely bad practice.
Dave - WØLEV
On Thu, Jan 23, 2025 at 10:41 PM <nlsa@nlsa.com> wrote:
> Dave & Jim -
> I confess to having slipped back into the "Earth is a noise sink"
> mentality.
> All of my electronic subsystems are mounted in aluminum enclosures that
> reside in racks inside the upper part of the antenna support. Assuming
> that the rack rails are bonded to each other and to the heavy ground
> conductor through the slip ring, do you think that being bolted to the
> common rails is a decent means of bonding the subsystems for near-miss
> lightning protection?
> Thank you,
> Michael, W9IP
>
> -----Original Message-----
> From: RFI <rfi-bounces+nlsa=nlsa.com@contesting.com> On Behalf Of David
> Eckhardt
> Sent: Thursday, January 23, 2025 4:28 PM
> To: jim@audiosystemsgroup.com
> Cc: rfi@contesting.com; Ham-Antennas <main@ham-antennas.groups.io>
> Subject: Re: [RFI] FW: RF noise and ground
>
> 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
> >
> >
> >
> > _______________________________________________
> > RFI mailing list
> > RFI@contesting.com
> > http://lists.contesting.com/mailman/listinfo/rfi
> >
>
>
> --
>
> *Dave - WØLEV*
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>
>
--
*Dave - WØLEV*
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