I have seen a number of these over the years. I have no real reason to want
a multi-band dipole myself but is there an advantage to having this type of
antenna ( with it's supposed vertical properties ) over an ordinary inverted
vee for a single band such as 75 meters? I have rotatables for 6-20mtrs
like most do. I just would like to be able to stick something up on the
tower ( I have only one, a crank-up with just a couple of palm trees
around )that will do a decent to GOOD job on 75 and if possible 40. So with
that in mind is there an advantage to something like a G5RV or OCF dipole
for 40 or 80 or 40/80? - Mike
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com]On Behalf Of w9nhq@myway.com
Sent: Monday, October 02, 2006 11:49 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] different OCF dipoles?
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._______________________________________________________________________
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