[TowerTalk] w7ekb & ground rods

[Jim Brown]

On Thu,1/22/2015 9:33 AM, Brian Carling wrote:
> So the text books say....
> However some of this is counter-intuitive

Science is not intuition.

> and very counter-empirical.

When you add wire to an antenna, you change the antenna.  When that 
antenna is a "long wire" or vertical, anything connected to the chassis 
of the radio becomes part of the antenna. These antenna types need a 
counterpoise to carry return current for the long wire -- either a 
resonant length of wire or radials. If we don't supply the return path, 
the antenna will use whatever is available to it, connected to earth or 
not.  One of those accidental return paths is the green wire that is 
part of the AC wiring in your home. It does NOT need to be connected to 
earth to carry return current -- it's often long enough on it's own to 
be an effective antenna. That power wiring will radiate your signal, 
conduct it to equipment where it will cause RFI, and it will receive 
noise. The only thing an earth connection does is change the length and 
shape of that half of the antenna.

The same thing happens with antennas like a dipole when there is no 
common mode choke on the feedline. The feedline, and everything 
connected to it, become part of the antenna.

73, Jim K9YC

>
> Best regards - Brian AF4K
>
>
>
>
>> On Jan 19, 2015, at 12:17 PM, Kelly Taylor <ve4xt at mymts.net> wrote:
>>
>> In most cases, RF ground is a fallacy. The right length of conductor can
>> make it so that there's zero difference RF-wise between having it connected
>> and having it not connected to the ground rod. A ground conductor starts
>> rapidly losing effectiveness RF-wise at one-tenth a wavelength (about 6' on
>> 10m) and longer.
>>
>> Also, as part of an antenna system such as a vertical, a ground rod (for RF
>> purposes) is next to useless. (Important for lightning protection, yes, but
>> not for RF.) Radials are the way to provide RF current return: a ground rod
>> is mostly very well insulated from picking up return currents.
>>
>> Dry soil has got to be less conductive than moist soil. I would think what
>> that means is multiplying the number of ground rods to make up for the lack
>> of conductivity, and perhaps encasing the rods in concrete or bentonite to
>> maximize whatever conductivity there is. You don't have to have the rods
>> vertical, either. You could lay them in trenches, and for concrete
>> encasement, you'd treat the ground rod much like you would rebar, suspending
>> it in the concrete during the pour.
>>
>> 73, kelly
>> ve4xt
>>
>>
>>
>>
>>> On 1/19/15 10:45 AM, "Ken" <wa8jxm at gmail.com> wrote:
>>>
>>> It seems to me that the ground above my rock layer (@ 36-40²)  gets really dry
>>> during the summer.  Does that dry dirt have enough conductivity to be useful?
>>> I do not know the answer to that question.
>>>
>>> Are there different answers depending on why we have the ground rod?  (RF
>>> ground, power line ground, or lightning protection)
>>>
>>> Ken WA8JXM
>>>
>>>
>>>> On Jan 19, 2015, at 12:53 AM, Kelly Taylor <ve4xt at mymts.net> wrote:
>>>>
>>>> It seems to me a valid question to ask on this thread: Do you gain anything
>>>> by, for example, drilling a hole to get a ground rod deeper?
>>>>
>>>> If you think about it, the answer might not be so simple.
>>>>
>>>> The point of a ground rod is to maximize electrical contact with the ground.
>>>> If you have to drill 48 inches of an eight-foot rod and don't employ some
>>>> kind of conductive filler (concrete, bentonite, etc.) to bond the rod to the
>>>> rock, how much better off are you than just putting in a 48-inch rod? Even
>>>> if you do use bentonite, is rock a good connection?
>>>>
>>>> If that's the case, what would be wrong with cutting the eight-foot rod into
>>>> two 48-inch rods and driving them 96 inches apart?
>>>>
>>>> The point of eight- or ten-foot ground rods is to get eight or ten feet of
>>>> contact area, not necessarily to get eight or ten feet deep, yes?
>>>>
>>>> Just curious on all this.
>>>>
>>>> 73, kelly
>>>> ve4xt
>>
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