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Re: [TowerTalk] Does prevailing grounding scheme promote large ground lo

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Does prevailing grounding scheme promote large ground loop?
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Sun, 24 Jul 2016 22:08:08 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On Sun,7/24/2016 7:09 PM, Dick Blumenstein wrote:
Thanks Jim for your input. I will have to study your presentations in more depth. Years ago, I worked building audio amplifiers and tape duplicators that also had a small oscillator for some AC bias needed for tape recorder recording heads. Ground loops at the time were always a concern and we had to make sure that we only grounded the entire system at one point to the chassis, and ran a ground rod suspended down the center of the chassis and grounded all components to that ground rod.

The problem with using the words "ground loop" is that it causes us to do the wrong thing to solve issues with hum, buzz, and RFI. The respected audio engineer Bill Whitlock is the guy who opened my eyes to understanding the REAL mechanisms, which are NOT a loop. I've incorporated his treatment into my tutorials, both for hams and for pro audio/video. Bill and I serve on the AES Standards Committee Working Group on EMC. He, I, Neil Muncy, and Ray Rayburn are principal authors of all AES Standards on EMC, with lots of input from other fine engineers -- ABC-TV, BBC, German broadcast, etc.


I noticed in one of your slides that you said to NOT run the tower grounding system back to the house AC input ground if it is too long (but to depend on the antenna coax sheath). How long is too long?

Note the slide(s) showing that 1) lightning is NOT a DC event, it is an RF event so that 2) the inductance of a long bonding conductor dominates the resistance of the conductor. The logic here is to give lightning at the tower a low impedance path to earth at its base, do the same at the house. And, of course, follow proper bonding at the house.

It is about 40-50' from my shack wall to the tower base, but probably 100' from the tower base to around the other side of the house to the AC input of the house (house ground rod). I am planning on putting in about 9 ground rods around the base of the 73' tall crank-up tower (3 off of each leg in a "Y" configuration). The first rod off of each Y leg will have a wide copper strap connected from the ground rod to the tower leg in a gentle arc with no sharp turns. Most installations I've seen have maybe a 3" or 4" wide piece of copper. All three Y base leg ground rods will be cadwelded to #2 copper stranded in a ring around the tower. It was this ring that I was going to run to the AC house ground rod. Finally, the other 2 ground rods in each Y configuration were planned to be cadwelded to the base leg of the Y with #2 stranded. Any comments? PS - We have heavy clay soil here in NC.

All sounds fine. I'd say the tower is probably close enough to the house that the tower ground should be bonded to the house. But remember, it's inductance, so a pretty high Z at 1 MHz, which is where the energy in lightning is roughly centered.

What matters a LOT more is proper bonding of everything in your house. See the tutorial for discussion of that.

73, Jim

Dick, K0CAT

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Jim Brown wrote on 7/24/2016 2:07 PM:
On Sun,7/24/2016 9:04 AM, Dick Blumenstein wrote:
one huge ground loop.

Ground loops are a massive fiction, a completely false concept. Here's my take on power, grounding, and bonding for hams.

http://k9yc.com/GroundingAndAudio.pdf

And here's my comparable work for professional audio and video, which I taught for ten years at conventions for audio and video contractors who build systems from the small to the very large. The first link is to a long tutorial, the second two are to Power Point slides for my workshops.

http://k9yc.com/SurgeXPowerGround.pdf

http://k9yc.com/InfoComm-PowerSystems2012.pdf

http://k9yc.com/InfoComm-Grounding2012.pdf

73, Jim K9YC


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