Mike, I suggest you may want to do some reading at L B Cebik's website www.cebik.com about vertical antennas. It would seem that what you have been reading/hearing has some 'garbage content' to it, or may be information specific to one installation. Start with basic antenna principles and work to apply that to your situational constraints and you will reward yourself with a better performing antenna system.
For a multiband elevated quarterwave vertical, I recommend using 2 electrical quarter wave radials for each band of use. Each radial pair should be oriented in opposing directions to cancel the horizontal component in the radiation pattern. If you do not wish to cancel the horizontal component, then a single radial for each band is all that is needed. Since you will have the base of the antenna well above ground, you must create a ground plane with the radials. A vertical monopole with its base on the ground will behave nicely with untuned radials buried in the ground and forming a ground screen, but with an elevated quarterwave vertical monopole, you must create 'the other half of the antenna' at the base - that is what the radials accomplish. An elevated monopole may be tuned by either trimming the length of the radiator or the length of the radials or both. Yes, think of the vertical and each of the radials as a dipole, bent at the feedpoint - in other words, as an upright "L" antenna fed at the corner. If you have multiple radials for each band, tune each one of them individually. for zero reactance at the base if you are using an antenna analyzer, but you can also tune for minimum SWR. Remember that a vertical monopole operating against a perfect ground (or complete radial screen) will have a feedpoint impedance of 35 ohms. If the radials slope downward instead of perpendicular to the vertical, the feedpoint impedance will be increased because the antenna system is approaching a dipole (which has a theoretical feedpoint impedance of 72 ohms). If you are feeding the antenna system with 50 ohm coax, you can expect some SWR on the line, so that part can be tuned out at the transmitter end. To keep radiation from the feedline to a minimum, run the feedline away from the antenna in-line with the radiator - it should drop for at least a quarterwave under the ground plane. Accomplishing that feat is usually not possible with the antenna roof mounted, so you will have to provide some in-line decoupling on the feedline. A balun (or unun) at the base will not accomplish all the decoupling required because the feedline will pick up radiation beyond the balun and try to act as a radial. A W2DU type current balun placed along the feedline will help a lot. I would suggest placing it at the point where the feedline exits the roof and changes direction. For lightning protection, yes use a heavy wire to ground from the base of the antenna. The radials should stop the radiation from this ground wire (BTW, there is nothing wrong with a vertical dipole). If your antenna already has a DC path to ground at the base, you will be all set, but if there is no DC path, you can install an RF choke there. An RF choke will also bleed off any static that will tend to build up on the antenna. 73, Don W3FPR > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Behalf Of Mike Walkington > Sent: Friday, March 02, 2007 5:56 AM > To: Elecraft-Reflector > Subject: [Elecraft] Vetical Antennas > > > Hi All, > > I've moved to a new house and I'm trying to get a Hustler 5BTV working > really well with my K2 in my new location. I plan to install the > antenna in > a ground plane configuration on a 2 storey home and feed it with > coax. I was > planning to use a few quarter wave radial for each of the bands > of interest. > > I've had problems with TVI using this antenna before, so this time I will > use some sort of a choke to block currents on the outer surface > of the coax > braid. Any suggestions on what I should use? > > How should I protect myself from lightning? I initially thought about > running a lead from the base of the antenna to ground, but the length of > this would probably turn the antenna into a vertical dipole. > > I was reading some doco for this antenna and read the following: Never use > an antenna tuner to tune the antenna.Use of a tuner only fools the > transmitter and does not correct a problem at the antenna. > This doesn't seem right can I use my K2's tuners? > > Finally, I've been reading Moxon's HF Antennas for All Locations, and he > doesn't seem to recommend quarter wave radials for ground planes. I'm not > sure I comprehend why. Is anyone familiar with his concerns? > > > Mike > VK1KCK, K2 #2599 > > _______________________________________________ > Elecraft mailing list > Post to: Elecraft@mailman.qth.net > 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: 7.5.446 / Virus Database: 268.18.5/706 - Release Date: > 2/28/2007 4:09 PM > -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.446 / Virus Database: 268.18.5/706 - Release Date: 2/28/2007 4:09 PM _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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
