[TowerTalk] RF Ground is a Myth

Mon Jan 19 21:16:05 EST 2015

Brian--
I worked in a 1000 acre plant that developed Rockets, for 38 years. Every 
building was on an Ufer ground system, but they were not as simple as has 
been described here.  The buildings had "Franklin" type rods at high points, 
coupled to the Ufer system by large copper cables. The Ufer system was 
supplemented with additional Copper cables in ditches around the perimeter.
Concrete needs no additional ingredients to be conductive. The Ufer system 
consists of the incorporation of a distributed set of conductors within the 
concrete which are, in turn, connected to a dissipation arrangement exterior 
to the protected structure.
I only remember one case of structure Lightning  damage in that 38 years, 
and that was caused by a painting crew having cut a cable and not reporting 
it for repair. In that incident, the failure was not in the Ufer 
arrangement, but in damage to the "Franklin" part. The damage was above the 
cut in the cable.
Bill--W4BSG

-----Original Message----- 
From: Brian Carling
Sent: Monday, January 19, 2015 7:29 PM
To: Chuck Dietz
Cc: towertalk at contesting.com ; jim at audiosystemsgroup.com
Subject: Re: [TowerTalk] RF Ground is a Myth

The advice varies about this considerably. This week is the first time I've 
even heard of UF ER or conductive concrete!

The professional experts that I know recommend putting a 20 to 30 foot 
ground rod into the ground at each corner of your house and connecting heavy 
gauge copper conductors up to lightning rodsup on the roof.

It seems like if the only thing you need is a large area of this allegedly 
conductive concrete stuck in the ground, why not ground everything to the 
concrete slab your house sits on!!

Best regards - Brian Carling
AF4K Crystals Co.
117 Sterling Pine St.
Sanford, FL 32773

Tel: +USA 321-262-5471

> On Jan 19, 2015, at 8:19 PM, Chuck Dietz <w5prchuck at gmail.com> wrote:
>
> From what you have said, I take it that putting a single (or even 2 or 3)
> ground rods on a tower base that is in a good bit of concrete is
> wasted effort?  The tower base and concrete should dissipate most of a
> lightning strike?
>
> Chuck W5PR
>
> On Mon, Jan 19, 2015 at 12:59 PM, Jim Brown <jim at audiosystemsgroup.com>
> wrote:
>
>> The real issue is that the concept of "RF Ground" is a myth and the 
>> result
>> of fuzzy thinking. Part of the reason is what Jim has addressed below. 
>> The
>> other reason is simply that a connection to earth does NOT make TX 
>> antennas
>> work better, and is NOT part of a solution to hum, buzz, or RFI. The 
>> earth
>> is NOT a sink into which noise and RF is dumped. The ONLY reasons for an
>> earth connection are to sink lightning current and other 
>> equipment-related
>> surge currents on the AC line.
>>
>> My late colleague, Neil Muncy, ex-W3WJE, taught classes on power and
>> grounding for many years to audio professionals, and I took over those
>> classes when he no longer had the health to do them. He is also the guy 
>> who
>> alerted the world to "The Pin One Problem" back in 1994. He gave one of 
>> my
>> favorite  teaching examples. He would say to a class, "park yourself at 
>> the
>> end of the runway of the nearest major airport with a good pair of
>> binoculars, and call me collect when you see an aircraft take off 
>> trailing
>> a ground wire."
>>
>> 73, Jim K9YC
>>
>>> On Mon,1/19/2015 9:15 AM, Jim Lux wrote:
>>>
>>> Are there different answers depending on why we have the ground rod? 
>>> (RF
>>>> ground, power line ground, or lightning protection)
>>> Yes..
>>>
>>> ground rods make terrible RF grounds, in general (where RF is HF and 
>>> up):
>>> skin effect means that wires and rods have high ac resistance. (skin 
>>> depth
>>> in copper at 10 MHz is about 0.8 mils/0.02 mm.)
>>>
>>> They also have significant series L (1 microhenry/meter for a wire.. so 
>>> a
>>> 30 foot run to the rod is a 10 uH inductor, that's 600 ohms reactive
>>> impedance.
>>>
>>> Rods are really for electrical safety ground and/or lightning ground. 
>>> And
>>> they don't work all that well for that, unless deployed in large 
>>> numbers.
>>> The advantage of a rod is that it's easy to install by driving, but as 
>>> an
>>> electrical connection to the earth, it's just not that wonderful: the
>>> surface area is quite small (8 foot rod, 1" in diameter is only 300 
>>> square
>>> inches.  You could probably do better, electrically, by burying a 1 foot
>>> square plate (288 square inches).
>>>
>>>
>>> Rods are also used in phone and power line applications.. you drive a 
>>> rod
>>> at every pole (or wrap the ground wire around the foot of the pole when
>>> planting it).  Even if any one rod has crummy characteristics, there's 
>>> lots
>>> of other rods in the circuit to help establish the common voltage 
>>> reference
>>> and provide a fault current return.  I've had telco installers drive a 
>>> new
>>> rod next to the existing rods on the general principle that at least 
>>> they
>>> knew the new rod was in good condition: faster to just do a new rod than 
>>> to
>>> test the existing one
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