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@tcaf.org > wrote:From: Eugene Hertz [mailto:
ehertz@tcaf.org]To: towertalk@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
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