[Elecraft] Lightning season is on the way in New Mexico.

[Don Wilhelm]

  Byron,

Thanks for posting that quote.
As a matter of importance, all "grounds" are not the same.  What we have 
been discussing is the Electrical Safety Ground, which IMHO is the most 
important one to be considered.  The safety of you and your family 
depend on it.

The RF return (antenna ground) does not have to be at earth ground 
potential (but usually will be when it enters the shack through a 
grounded coax connector).  If you think of this as the antenna RF Return 
rather than as ground, the situation may be a bit clearer.  The RF 
Ground point is that reference point determined by your antenna - for a 
center fed balanced antenna, it is that point where the antenna current 
passes through zero and changes phase at some point between the feedline 
connections to the radiator(s).  This point is obviously not earth 
ground, but it should be considered the RF Ground point for that antenna.
A vertical with grounded radials is similar, but a better term for the 
radial field is "RF radial screen" than using RF Ground, which it may or 
may not be.

Chassis ground is another example.  In some pieces of equipment, it is 
isolated from the Safety Ground - consider a power supply with an 
isolated return terminal - or consider equipment that is powered from a 
battery, there is no need to connect its common to the AC Safety ground 
for it to be functional, but if there are exposed areas of that return 
ground that are likely to be touched (that ground is connected to a 
metallic enclosure), then it should be connected to the AC safety ground 
even when operated on batteries.

Lightning and transient dissipation ground is a different animal 
altogether.  The currents can be huge, and the frequencies involved are 
all over the RF spectrum.  The principle behind any lightning protection 
grounding is to provide enough low impedance conductors in the earth to 
dissipate that surge over as large an area of the earth as possible - 
that takes a lot of ground rods spread over a large area and very fat 
conductors between them.  Yes, that system of ground wires and rods must 
also be connected to the AC entry ground rod unless the distance between 
those two grounds is at least 150 feet apart.  Towers, fences, and 
anything metallic within that 150 foot radius should also be connected 
to that Lightning and Dissipation ground system.  If in doubt, connect it.

I refer you to the writings of Ron Block - I consider his information on 
lightning protection for the ham shack authoritarian.  He published a 3 
part article in QST beginning in June 2002 (Google for lightning 
protection Ron Block).  I suggest reading it if ham station protection 
is one of your goals.  It is the document I considered "golden" when I 
was setting up the ground system for my station and antennas.  I was 
dealing with new construction which made installation a bit easier, but 
I have tried to implement as many of his recommendations as possible, 
including perimeter wires around the buildings.  Even so, I do not 
operate when a lightning storm is nearby.  No matter how good your 
protection installation may be, it is not to be trusted for a direct 
hit.  Disconnect the equipment and get out of the shack.

73,
Don W3FPR



On 3/28/2011 7:15 PM, Byron Servies wrote:
> begin quote
>
> 28.1.8 Grounds
>
>      As hams we are concerned with at least four kinds of things called
> "ground," even if they really aren't ground in the sense of connection
> to the Earth.  These are easily confused because we call each of them
> "ground."
>          1) Electrical safety ground (bonding)
>          2) RF return (antenna ground)
>          3) Common reference potential (chassis ground)
>          4) Lightning and transient dissipation ground
>
>      IEEE Std 1100-2005 (also known as the "Emerald Book," see the
> Reference listing, section 28.1.13) provides detailed information from
> a theoretical and practical standpoint for grounding and powering
> electrical equipment, including lightning protection and RF EMI/EMC
> concerns.  It's expensive to buy but is available through libraries.
>
> end quote.
>