Some lightning facts: There is no amount of grounding that will help protect an antenna from lightning damage. Grounding will not help an antenna or tower from being struck by lightning. However if a lightning rod is placed above the antenna or a wire sloping down from above and around the antenna it will intercept a lightning strike and prevent the antenna from being hit. It would be important to have the lightning rod/wire well bonded to the tower and the tower well grounded.
A well grounded tower and antenna bonded well to the tower will help prevent damage to other equipment tied to the antenna. Also feedlines should be well bonded to the tower at top and bottom. Ground rod surface area is much less important than length. Extra surface area contributes little to rod effectiveness. Too long of a ground rod and the extra length becomes ineffective due to the high inductance of the long length. Several ground rods spaced approximately the sum of the length of two adjacent rods is most effective. A good lightning ground consist of a low impedance, low resistance and high capacitance coupling to earth. Lightning is composed of very low (DC) and high frequencies (peak at around 1 MHz). If many ground rods are used in a star configuration, it is not necessary to use large wire connecting all the rods as the lightning energy will be divided between all paths so less current flows on any individual wire. If ground rods are placed in a star configuration it does no good to add rings of wire connecting the rods together. The lightning energy travels in a straight line out away from the tower on each radial and each radial carries equal current. So there is no difference of potential between rods or radials. Copper strap for ground connections will reduce the inductance thus lowering the impedance of the path. A separate heavy copper wire or strap running down a tower tied to the antenna to ground is a waste of copper. The tower itself is a much lower inductance path than what a separate ground wire provides. 73 Gary K4FMX > -----Original Message----- > From: Repeater-Builder@yahoogroups.com [mailto:Repeater- > buil...@yahoogroups.com] On Behalf Of Eric Lemmon > Sent: Monday, June 29, 2009 7:42 PM > To: Repeater-Builder@yahoogroups.com > Subject: RE: [Repeater-Builder] DC Ground Lightning Protection on > antenna???? > > If the tower is bolted to galvanized pipe that is embedded in concrete of > which a significant amount is in contact with soil, you have a > "concrete-encased grounding electrode" which is hard to improve upon. It > is > not likely that a ground rod would be worthwhile, since damp concrete > (concrete in intimate contact with soil at grade level) is a fairly good > conductor, and such a footing or foundation has hundreds of times the > surface area of a ground rod. Just be certain that your station equipment > is solidly bonded to the tower and to the electrical service neutral with > a > #6 AWG or larger copper conductor. > > Specific guidance for the grounding and bonding of radio and television > antennas, including Amateur Radio systems, is found in Article 810 of NFPA > 70, the National Electrical Code. > > 73, Eric Lemmon WB6FLY > > > -----Original Message----- > From: Repeater-Builder@yahoogroups.com > [mailto:repeater-buil...@yahoogroups.com] On Behalf Of agrimm0034 > Sent: Sunday, June 28, 2009 9:34 PM > To: Repeater-Builder@yahoogroups.com > Subject: [Repeater-Builder] DC Ground Lightning Protection on antenna???? > > > > I bought a nice looking RFS Celwave antenna to use on 462.600 Specs are DC > ground for lightning protection but is there something I need to do to > make > sure it is protected? It sits on 3 legged tower 40 ft up and the tower is > mounted on the side of a structure. It sets on 3 pieces of galvanized pipe > that are set in concrete. Overall the tower is grounded just not as good > as > what I could make it be. If I ran a grounding rod into the ground and ran > #8 > or heavier wire to the tower would I just be wasting my time to protect > the > antenna or what should I do to make sure everything is protected ok. > Thanks > > > > ------------------------------------ > > > > Yahoo! Groups Links > > >
