If *all* connections to the K9AY antenna (including 'sneak' paths) are isolated from the AC mains ground, the safety factor does not exist. The ground required by the K9AY antenna is an RF ground which is not necessarily (but may be) at the same potential as the AC mains ground and safety ground. BUT, that same isolation may lead to ground currents that defeat the low noise characteristics of the K9AY antenna. Ideally, all "mother earth" grounds should be connected to the AC mains ground by a wire.
Often the building inspector likes to see the AC mains ground buried beneath the surface of the earth so it is not subject to being hit by lawn mowers or other instruments of destruction. There will be a bare #6 (or larger) wire going into the earth at your AC mains entry point - that is the wire that you must connect to. Look for the type of connector that is used by the telephone company connection to this ground wire - it is usually a "U" shaped clamp with a nut for tightening. Those type clamps are available at your local DIY store in their electrical department. 73, Don W3FPR Richard S. Lindzen wrote: > Dear Don, > > This leaves me a bit concerned. I am planning to put up a K9AY > receiving antenna in my backyard and it is supposed to be connected to > a ground rod. I had never seen it suggested that this must be > connected to the utility ground stake. I'm not even sure where the > utility ground stake is. I've never noticed one though I will ask my > electrician. If there is one, it is likely to be pretty far from the > K9AY. > > 73, > > Dick, KA1SA > > At 10:22 PM 1/20/2010, Don Wilhelm wrote: >> Joe, >> >> That is *one* reason *any* ground rod should be tied back to the utility >> ground stake. It is as requirement of NEC, and should not be ignored. >> If you drive ground rods for the ham station, connect those ground rods >> to the utility entrance ground rod - no exceptions. The ideal is #6 or >> larger wire, but if you cannot do that use whatever wire you can. Your >> safety depends on it. If you cannot connect extra ground rods to the AC >> mains entry ground, then do not drive those extra ground rods - they are >> *not* an RF ground (see my many posts in the archives on that topic) - >> and as Joe points out, in the event of a lightning strike (or equipment >> fault), they may create a dangerous condition. >> >> You have 3 "grounds" to consider in the hamshack - 1) The AC safety >> ground, 2) The lightning path ground, and 3) The RF ground. >> 1) and 2) may be one and the same, but 3) is a "horse of a different >> color", and has nothing to do with a "mother earth" ground - it is a >> point of low impedance at the frequency of interest, and usually exists >> at some point in the antenna system, quite apart from "mother earth". >> The English folks have the language a bit better and refer to "earthing" >> which is often apart from "grounding", but we here in the US use the >> same term for all common connections and in the process create confusion >> for ourselves. >> >> 73, >> Don W3FPR >> >> Joe Subich, W4TV wrote: >> > This creates a situation that is potentially hazardous >> > to your equipment. The AC "third (green) wire" is supposed >> > to be connected to ground only at the main panel/service >> > entrance. However, since it is connected to the chassis >> > of the power supply, it is also connected through the power >> > supply and radio to ground via the coaxial cable. >> > >> > If the point at which the coaxial cables enter the building >> > is not the same place that power enters the building, any >> > nearby lightning strike can set up a significant difference >> > in voltage between the power line "safety ground" and the >> > RF ground (feedline shields/tower). That difference can >> > fry any electronics connected to both "grounds." >> > >> > There are techniques for dealing with this problem ... but >> > they are not necessarily easy or inexpensive. >> > >> > 73, >> > >> > ... Joe, W4TV >> > >> > >> > >> > >> > >> > >> >> -----Original Message----- >> >> From: elecraft-boun...@mailman.qth.net >> >> [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Don Wilhelm >> >> Sent: Wednesday, January 20, 2010 8:01 PM >> >> To: David Woolley (E.L) >> >> Cc: Rich; elecraft@mailman.qth.net >> >> Subject: Re: [Elecraft] Grounding negative side of power supply? >> >> >> >> >> >> The AC side should always be connected to the power supply chassis - >> >> unless it is of the "double insulated" design where no ungrounded >> >> metallic part can come into contact with the human body. >> >> Yes, cutting >> >> the AC "green wire ground" is a dangerous thing indeed - the entire >> >> chassis could rise to the AC mains voltage in the event of a fault. >> >> >> >> The power supply negative *can* certainly be floating *if* >> >> the designer >> >> made provisions for doing that. It requires that all the common >> >> connections on the secondary side of the transformer are >> >> isolated from >> >> ground. As I recall, Astrons are not built that way. >> >> >> >> 73, >> >> Don W3FPR >> >> >> >> David Woolley (E.L) wrote: >> >> >> >>> Rich wrote: >> >>> >> >>> >> >>>> I had a situation with an older (analog) power supply >> >>>> >> >> (that had its >> >> >> >>>> negative side grounded to the main AC ground) that tripped >> >>>> >> >> the Ground >> >> >> >>>> Fault Circuit Interrupter (GFCI) in one of the bathrooms. >> >>>> Eliminating the bond to ground >> >>>> >> >>>> >> >>> I consider this dangerous advice. If you have an ELCB >> >>> >> >> tripping, you >> >> >> >>> do >> >>> not treat the problem symptomatically, by creating an >> >>> >> >> unsafer system, >> >> >> >>> you find out what the real problem is and you fix it. >> >>> >> >>> I can't tell what the exact wiring configuration is here, but it is >> >>> very >> >>> likely that you have created a situation where there are >> >>> >> >> pieces of metal >> >> >> >>> in reach which have low impedance paths to very different "earths". >> >>> >> >>> >> >>> >> >> ______________________________________________________________ >> >> Elecraft mailing list >> >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> >> Help: http://mailman.qth.net/mmfaq.htm >> >> Post: mailto:Elecraft@mailman.qth.net >> >> >> >> This list hosted by: http://www.qsl.net >> >> Please help support this email list: http://www.qsl.net/donate.html >> >> >> > >> > ______________________________________________________________ >> > Elecraft mailing list >> > Home: http://mailman.qth.net/mailman/listinfo/elecraft >> > Help: http://mailman.qth.net/mmfaq.htm >> > Post: mailto:Elecraft@mailman.qth.net >> > >> > This list hosted by: http://www.qsl.net >> > Please help support this email list: http://www.qsl.net/donate.html >> > >> ------------------------------------------------------------------------ >> > >> > >> > No virus found in this incoming message. >> > Checked by AVG - www.avg.com >> > Version: 9.0.730 / Virus Database: 271.1.1/2634 - Release Date: >> 01/20/10 04:12:00 >> > >> > >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:Elecraft@mailman.qth.net >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html > > ================================================== > Richard S. Lindzen > Alfred P. Sloan Professor of Atmospheric Sciences > Office: 54-1720, MIT > Cambridge, MA 02139 USA > 1 (617) 253-2432 (voice) > 1 (617) 253-6208 (fax) > > Temporary Home: 100 Memorial Drive > Apt. 2-2a > Cambridge, MA 02142 USA > 1 (617) 945-5784 (voice) > ================================================== > ------------------------------------------------------------------------ > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 9.0.730 / Virus Database: 271.1.1/2634 - Release Date: 01/20/10 > 04:12:00 > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
