[RFI] FW: RF noise and ground

[nlsa at nlsa.com]

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 at contesting.com> On Behalf Of David Eckhardt
Sent: Thursday, January 23, 2025 4:28 PM
To: jim at audiosystemsgroup.com
Cc: rfi at contesting.com; Ham-Antennas <main at 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 at audiosystemsgroup.com> wrote:

> On 1/23/2025 4:30 AM, nlsa at 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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