Jim, Actually a half wavelength run to a ground rod will produce a low impedance at the shack end - if the ground rod is truly a good RF ground (sometimes it is and sometimes not). So yes, it can have a positive influence, but it will not guarantee it (the effectiveness depends on the ground characteristics at the grounded far end) - the half wave wire only repeats what it has on the other end.
Yes, we agree that a proper antenna system is the ideal solution, and that quarterwave counterpoises can help (as long as the user remembers that the quarter wave starts at the antenna tuner or transceiver - it seems that subtle fact is often overlooked or ignored). 73, Don W3FPR > -----Original Message----- > From: JIMMY D HARRIS [mailto:[EMAIL PROTECTED] > Sent: Tuesday, January 23, 2007 7:40 PM > To: [EMAIL PROTECTED]; [email protected] > Subject: RE: In Shack Radials and Ground > > > Don, > > Maybe my thinking is too simple. But here goes. I believe that we both > have indicated that quarter wavelength can eliminate RF in the > shack among > other RF problems caused by less than a perfect antenna system. > I believe > that we also agree that a half wavelength does not do that. Therefore, a > half wavelength ground wire has no positive influence on RF > problems. That > indicates to me that I should avoid half wavelength ground runs > as they have > no positive influence on RF problems. I would guess in the world > of amateur > radio there are RF problems that are not recognized. Half wavelength > grounds runs do nothing to clear up those problems. Of course, the real > solution is to have an adequate antenna system. You can bet that in > commercial systems a proper antenna system is used. > > Jim, AB0UK > > > >From: "Don Wilhelm" <[EMAIL PROTECTED]> > >Reply-To: <[EMAIL PROTECTED]> > >To: "JIMMY D HARRIS" <[EMAIL PROTECTED]> > >Subject: RE: In Shack Radials and Ground > >Date: Mon, 22 Jan 2007 23:23:09 -0500 > > > >Jim, > > > >The way I read your post was that half wave lengths of wire to the ground > >rod are things to stay away from. Perhaps I mis-understood your intent - > >but you did say to stay away from ground rod runs that are a > half wave or a > >multiple thereof, and that is the incorrect part. > > > >Yes, the run to the ground rod can radiate - but that is not > necessarily a > >bad thing. > > > >The really best place to create the RF Ground is at the antenna (or its > >feedpoint), but not all folks are blessed with a controllable > situation and > >must resort to other 'cures' like tuned counterpoise wires. > > > >I have no RF in the shack problems here, all my antennas have an > effective > >RF ground as an integral part of their design (no OCF antennas > here), and I > >have to suffer with a 150 foot run of coax before I get to the > distribution > >point going to the antenna field. It keeps the RF out of the shack, but > >requires low loss coax runs. > > > >73, > >Don W3FPR > > > > > -----Original Message----- > > > From: [EMAIL PROTECTED] > > > [mailto:[EMAIL PROTECTED] Behalf Of JIMMY D HARRIS > > > Sent: Monday, January 22, 2007 10:46 PM > > > To: [EMAIL PROTECTED]; [email protected] > > > Subject: RE: [Elecraft] In Shack Radials and Ground > > > > > > > > > Don, > > > > > > I'm not sure we disagree. I seems like we are both are > agreeing to stay > > > away from quarter wavelength ground runs (wires) and use half > > > wavelength. > > > That is what I intended to say. Usually ground systems are not > > > effective RF > > > grounds. The connecting wire may be a relatively effective > > > radiator or an > > > element in tuning an antenna system. > > > > > > Jim, AB0UK > > > k2/100 S/N 4787 > > > > > > > > > >From: "Don Wilhelm" <[EMAIL PROTECTED]> > > > >Reply-To: <[EMAIL PROTECTED]> > > > >To: "JIMMY D HARRIS" <[EMAIL PROTECTED]>,<[email protected]> > > > >Subject: RE: [Elecraft] In Shack Radials and Ground > > > >Date: Mon, 22 Jan 2007 22:27:08 -0500 > > > > > > > >Jim, > > > > > > > >Sorry to disagree - consider what happens on a quarterwave wire: > > > It has a > > > >low impedance at one end and a high impedance at the other > end. Think > > > >about > > > >what will happen if you connect the far end of a quarter > wave wire to a > > > >good > > > >ground (low impedance) - the other (near) end will have a high > > > impedance at > > > >that frequency, and will not serve as an RF ground at all (in fact > >quite > > > >the > > > >opposite). > > > > > > > >A halfwave wire however can have a low impedance at each end, so > > > grounding > > > >the far end of a half wave wire will make the near end at a > similarly > >low > > > >impedance. > > > > > > > >A grounded radial and a counterpoise wire are two different things - > >the > > > >counterpoise wire creates a low impedance (about 35 ohms) by > nature of > > > >having the far end ungrounded, whereas a grounded (or buried) > > > radial forms > > > >a > > > >screen or reflector - yes, the counterpoise will radiate because > > > it becomes > > > >a part of the antenna system. The counterpoise controls the > radiation > > > >instead of having it wander willy-nilly around the shack and other > >places > > > >where it should not be present. > > > > > > > >I do understand that this is not intuitive - we have to > think in terms > >of > > > >antenna theory when dealing with RF grounds - what works fine at > > > DC and low > > > >frequency AC does not necessarily work at RF. > > > > > > > >Ground rods can be a good RF ground, but the wire connecting the > > > ground rod > > > >to the shack may not behave as expected - a 16 foot connection to the > > > >ground > > > >rod will present a high impedance to 14 MHz RF at the shack end - but > > > >should > > > >be a good RF ground for 10 meters since it is a halfwavelength away > >from > > > >the > > > >low impedance ground rod. > > > > > > > >73, > > > >Don W3FPR > > > > > > > > > -----Original Message----- > > > > > > > > > > There was mention about ground rods not being a good RF > > > ground. For the > > > > > most part I agree with that. However, the wiring to the > > > ground rod is > > > >in > > > > > fact a radial that is some part of a wavelength long. As we know > > > >quarter > > > > > wavelength radials can tune out RF. By the same token other > > > fraction > > > >of > > > > > wavelength ground runs (radials) can create RF in the shack > > > when used in > > > > > conjunction with a poorly designed antenna system. Stay away from > > > >ground > > > > > runs that are halfwave wavelength (or near) or multiples > thereof of > > > > > frequencies your antenna system is designed for. > > > > > > > > > > 'nough said...... > > > > > > > > > > Jim, AB0UK > > > > > K2/100 S/N 4787 > > > > > > > > >-- > > > >No virus found in this outgoing message. > > > >Checked by AVG Free Edition. > > > >Version: 7.5.432 / Virus Database: 268.17.4/644 - Release Date: > >1/22/2007 > > > >7:30 AM > > > > > > > > > > > > > _______________________________________________ > > > Elecraft mailing list > > > Post to: [email protected] > > > You must be a subscriber to post to the list. > > > Subscriber Info (Addr. Change, sub, unsub etc.): > > > http://mailman.qth.net/mailman/listinfo/elecraft > > > > > > Help: http://mailman.qth.net/subscribers.htm > > > Elecraft web page: http://www.elecraft.com > > > -- > > > No virus found in this incoming message. > > > Checked by AVG Free Edition. > > > Version: 7.5.432 / Virus Database: 268.17.4/644 - Release Date: > > > 1/22/2007 7:30 AM > > > > >-- > >No virus found in this outgoing message. > >Checked by AVG Free Edition. > >Version: 7.5.432 / Virus Database: 268.17.4/644 - Release Date: 1/22/2007 > >7:30 AM > > > > > -- > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.5.432 / Virus Database: 268.17.8/648 - Release Date: > 1/23/2007 11:04 AM > -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.432 / Virus Database: 268.17.8/648 - Release Date: 1/23/2007 11:04 AM _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
