>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@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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