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. > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
