[TowerTalk] Does prevailing grounding scheme promote large ground loop?

[Jim Brown]

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
>
> =======================
>
>
>
> 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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