[TowerTalk] different OCF dipoles?

[w9nhq at myway.com]

I have used the Buckmaster high-power OCF Dipole for nearly a year and it works quite well - for a multi-band dipole.  It is based on the (German) Fritzel FD-4 antenna and uses a 6:1 balun at the feedpoint.  The location of the feedpoint provides the greatest number of ham bands where the antenna's impedance is approximately 300 ohms.  Originally, this was 80, 40, 20 and 10 meters, but it was later discovered that 17, 12 and 6 meters also worked.  The 6:1 balun takes care of converting 300 ohms down to 50 ohms.  Some bands have higher or lower characteristic impedances, but even 200 or 400-ohm impedances become reasonable after the 6:1 balun does its job.  My antenna exhibits a maximum SWR of 2:1 (across the entire 80/75 meter band) and lower SWRs on the higher bands.  It is not designed to work on 30 or 15 meters - even with an external tuner, since forcing too much power on those bands could blow the balun. The Carolina Windom uses a more conventional 4:1 balun and the 
lengths are somewhat different in an attempt to accommodate that balun.  The Carolina usually needs an antenna tuner, since the 4:1 balun doesn't provide as good a match to coax as the 6:1 in the Buckmaster (who also makes the same antenna sold by Alpha-Delta).  The "vertical radiation" is more sales hype than something useful.  All off-center-fed dipoles will exhibit some feedline radiation.  I put a 1:1 current choke-balun between the Buckmaster's 6:1 balun and my coax, because I didn't want feedline radiation and since this was something done in the later versions of the Fritzel.   A good explanation of the antenna design can be found here:    http://www.xs4all.nl/~pa0fri/Ant/FD4/fd4eng.htm 73, Bill - W9NHQ --- On Mon 10/02, Eugene Hertz < ehertz at tcaf.org > wrote:From: Eugene Hertz [mailto: ehertz at tcaf.org]To: towertalk at contesting.comDate: Mon, 02 Oct 2006 04:20:51 +0000Subject: [TowerTalk] different OCF dipoles?Hello all,I am thinking of abandoning an original idea 
for a fan inverted-L and instead going for a windom/ocfd. I saw a few mfg of these for up to 80m and while they both had very similar total length, the length of the legs were rather different:Buckmaster 7-band OCF: 45' + 90' = 135' total (claim: 75/80, 40, 20, 17, 12, 10, & 6 meters)Carolina Windom OCF: 50' + 83' - 133' total (claim 80-10m)Others ocf mfg's have similar length legs.Another point of confusion for me. The buckmaster does not have a predefined vertical component. You add your own coax and they say the length is not critical. The carolina (and others) have a specific 22' vertical radiator and then you add your own coax after a "line isolator" Would anyone be willing to help me unravel these mysteries? First: What is the effect of the different leg lengths?Second: What is the impact of having/not having a specific length radiator vs just add coax.______________________________________________________________________________________________TowerTalk mailing 
listTowerTalk at contesting.comhttp://lists.contesting.com/mailman/listinfo/towertalk

_______________________________________________
No banners. No pop-ups. No kidding.
Make My Way  your home on the Web - http://www.myway.com