[TowerTalk] RF Ground is a Myth

[Jim Brown]

You misunderstand what Jim Lux and I have been saying.  Accepted good 
engineering practice for grounding a tower is 2-3 rods extending 
radially outward from each leg of the tower, bonded to the tower, with a 
Ufer ground built as a Ufer and also bonded to the tower.

73, Jim K9YC

On Mon,1/19/2015 5:19 PM, Chuck Dietz 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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