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Author Topic: Hanging an OCF dipole / Windom?  (Read 10674 times)
WALTERB
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Posts: 534




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« on: April 09, 2012, 07:17:21 AM »


I’ve seen diagrams like the one below.

http://www.mds975.co.uk/Images/amateur_radio/windom_bucomm_002.png

Does anybody  know if this is a preferred configuration or is it just an easier configuration than having it flat?
I saw another diagram that showed that “electrically” hanging it with the center support pole about 10 feet away from the balun, but mechanically this isn’t the best.

 If this only gains about 5 percent performance, then its not worth worrying about for my purposes.  If the performance gain is significant then I want to hang it using whatever method would give me that gain.

Thanks in advance.
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KC9TNH
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Posts: 304




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« Reply #1 on: April 09, 2012, 07:50:04 AM »

Just going from the diagram you linked to this would be the consideration if someone was lot-size limited or couldn't get the ends as high as the center, for whatever reason. If you can get it up to the center height and flat out to the full-length, no reason to worry about the hypotenuse of either side. I've read nothing yet that suggests that an Inverted-V config - all else being equal - is a benefit over a flat-topped dipole, OCF or not. If one has constraints (limited horizontal space) by all means get the wire up rather than make it shorter. (Willing to learn if someone has another take on it.)

My own OCFD works great (4:1 current balun); couple folks who mentored me through that mentioned the angle was less important than getting every inch of the wire out there, especially where on 80m a little means alot. Mine is basically flat, maybe 'just' a tiny bit tired...
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73
Wes -KC9TNH
"Don't get treed by a chihuahua." - Pete
WB6BYU
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Posts: 15674




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« Reply #2 on: April 09, 2012, 07:56:08 AM »

That's simply the configuration you get when the ends are at least 8' off the ground.  A higher mast
will make the central angle sharper, which isn't necessarily as good when the ends are at 8'.

The best approach is to get as much of the antenna up as high as possible.  While it may not make
much difference on 40m and 80m, overall performance is usually better on the higher bands when
the antenna is as flat as possible.  If you have space, tie a rope to the ends and run it out as far
as possible before tying it off - that gets the ends higher off the ground.

You want the ends out of reach for safety, but the losses also increase as they are brought
close to the ground.  The cause of the degradation on the higher bands is the harmonic
operation of the sloping wire.  Here is an article on that:

http://www.cebik.com/content/a10/wire/vang.html
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WALTERB
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Posts: 534




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« Reply #3 on: April 09, 2012, 07:59:53 AM »

Just going from the diagram you linked to this would be the consideration if someone was lot-size limited or couldn't get the ends as high as the center, for whatever reason. If you can get it up to the center height and flat out to the full-length, no reason to worry about the hypotenuse of either side. I've read nothing yet that suggests that an Inverted-V config - all else being equal - is a benefit over a flat-topped dipole, OCF or not. If one has constraints (limited horizontal space) by all means get the wire up rather than make it shorter. (Willing to learn if someone has another take on it.)

My own OCFD works great (4:1 current balun); couple folks who mentored me through that mentioned the angle was less important than getting every inch of the wire out there, especially where on 80m a little means alot. Mine is basically flat, maybe 'just' a tiny bit tired...


thanks.  I currently have one between two pine trees in my yard.  space isn't a problem.  It is hanging in a "V" (not an inverted "V")  because of the weight of the coax and balun, and the fact that I need some play in the line during storms.  Its been up for 11 months and I've worked New Zeland and Asiatic Russia with it on 100 watts from Southern Illinois.

If putting a pole under it to bring it up flat or inverting it would make it perform better, then thats easily done, but I don't want to go to the hassle if its only going to give me a slight edge.

I'm pretty sure that the current "V" configurtion is probably the worst of the three configs we have discussed.

thanks
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KD0FN
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Posts: 1




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« Reply #4 on: May 14, 2012, 02:09:19 PM »

I recently put up a 33' OCF at 25' high between two trees and fed it with a pair of RG-6 75 ohm cables about 50' to a tuner. Seems to work real well on 20-15-10. I need to make a change to my old IC-740 so I can try it on 17 as well. The thing runs WNW - ESE. Works great to Europe and NE US. Odd that I also seem to get good reports from SE US off the longer end as well . . .
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KC9TNH
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Posts: 304




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« Reply #5 on: May 14, 2012, 06:13:02 PM »

Odd that I also seem to get good reports from SE US off the longer end as well . . .
I also noticed (unexpected) good results off the long end.
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73
Wes -KC9TNH
"Don't get treed by a chihuahua." - Pete
W1JKA
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Posts: 2034




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« Reply #6 on: May 15, 2012, 12:38:51 AM »

Ditto for the above: my two ocf windoms also get the best dx off the long ends and 20 ft. height works better than 30 ft. height for my particular ground conditions.
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KU3X
Member

Posts: 307




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« Reply #7 on: May 16, 2012, 11:55:58 AM »

First of all you are mislead by the manufacture. It is an off center fed antenna, it is NOT a Windom. A true Windom is a vertical arry with an off center tap on the top hat. The entire array is fed against a ground radial system.
Now that we have determined you were looking at an Off Center Fed antenna, you erect it like you would a dipole.
In other words, what is pictured is an 80 meter OCF. So....on 80 meters it will radiate the same as a standard 80 meter
center fed dipole. Both are 1/2 wave 80 meter antennas fed at two different impedance points along the wire.

If you like inverted vee type antennas, than erect the OCF as an inverted vee.  There is no secret formula to mounting an
OCF. For better low angle radiation, mount it as high as you can. If you can not, just erect it in the best way you can.

My OCF80 is mounted at 55 feet as an inverted vee at my primary location. Works great on all bands. I work a lot of DX
with it from 10 to 80 meters. When I set up portable, I put the balun at 30 feet and tie the ends about 4 feet above the
ground. Again, I work lots of DX and it works great.

Here are what the radiation patters look like for numerous OCFs on all bands.
http://www.hypowerantenna.com/products/off-center-fed-antenna/off-center-fed-radiation-pattern#80meter

The key to this antenna is, "it is a resonant antenna on numerous bands. " It is not resoant on 15 meters. You are feeding
this antenna at a voltage point on 15 meters and that can damage the balun.

Barry, KU3X
« Last Edit: May 18, 2012, 08:18:19 AM by KU3X » Logged
N5LON
Member

Posts: 4




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« Reply #8 on: April 30, 2016, 10:09:38 AM »

First of all you are mislead by the manufacture. It is an off center fed antenna, it is NOT a Windom. A true Windom is a vertical arry with an off center tap on the top hat. The entire array is fed against a ground radial system.

Barry, KU3X

I disagree entirely.  YOu just described a Carolina Windom.  A true Windom, or OCFD (same thing) does not have a vertical radiator.  The Carolina Windom came from the minds of some CBer type guys and there's a lot of information out there that disputes the vertical radiator being of any real value (but you won't get the truth from a guy that's trying to sell you a Carolina Windom).  I don't doubt that guys with a CW aren't having great success, but a standard Windom is probably more efficient.
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WB6BYU
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Posts: 15674




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« Reply #9 on: April 30, 2016, 12:08:18 PM »

Quote from: N5LON

...A true Windom, or OCFD (same thing) does not have a vertical radiator...



You're not going back far enough in time.

The original Windom (as described by, but not invented by, Loren Windom 8GZ(?),
back in the late 1920's or so I think) was a half wave antenna with a single wire
feed from the output of the transmitter to the magic tapping point on the antenna.
With the right tap point, the standing waves on the vertical wire were minimized,
so that part radiated more as a traveling wave antenna.

This worked reasonably well on 40m and 80m, where the single wire feeder wasn't
too long (in wavelengths), and often could be matched on multiple bands because
transmitter output circuits had lots of tuning range and hams only cared if the
transmitter could produce rated power - SWR meters were rare.  In Europe it was
popular to feed it with a wire that was half the diameter of the antenna wire, which
was supposed to improve the match.  Of course, on the other bands the whole thing
worked mostly like a random wire, sometimes with most of the radiation from the
vertical wire, but it did radiate.  Coax cable was not as common for hams prior to
WWII, and this was often a reasonable approach that eliminated the need for
building open wire line for a doublet.

The idea of feeding it with twinlead as an OCFD seems to have popped up in the
1950's or 1960's.  It was shown in my 1968, ARRL Handbook, and was the
first antenna I tried as a Novice since my transmitter had a parallel-tuned output.
I never got it to work.

But that was also prior to effective current balun designs.  At some point, perhaps
in the 60's or 70's, we saw the appearance of the coax-fed OCFD design with a 4 : 1
voltage balun at the feedpoint, wound on a ferrite rod.  (Toroid cores were still
uncommon.)  Because of the unbalanced load, this would have had a lot of common
mode current on the outside of the coax.

I really don't remember OCFD designs becoming popular until at least the 1980's
as more hams were using solid state rigs.


But the point of that tangent down memory lane was to point out that the "Windom",
though bearing a superficial resemblence to an OCFD, used a different feed system
and, while operation on the fundamental band might be similar, on other bands the
current distribution on the two wires was often different, resulting in different patterns.
The original Windom certainly wouldn't have had a low SWR relative to 50 ohms over
multiple bands - the feedpoint impedance was closer to 600 ohms, fed against ground.
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KE6EE
Member

Posts: 1265




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« Reply #10 on: April 30, 2016, 01:13:39 PM »

Does anybody  know if this is a preferred configuration or is it just an easier configuration than having it flat?

If this only gains about 5 percent performance, then its not worth worrying about for my purposes.  If the performance gain is significant then I want to hang it using whatever method would give me that gain.

It's an easier configuration and good for many uses.

The idea of maximizing performance in some sort of general way for a multiband antenna may not be very useful. Considering antenna gain really requires defining specific bands, azimuths and radiation angles.

If the antenna is installed as suggested in the drawing so that the center is just 1/8 or 1/4 wavelength above ground on the lowest bands (presumably 80M and 40M) you have more or less an all-azimuth cloud warmer. On 20M and thereabouts you may have some basically bi-directional lobes with some gain. Ditto on the highest bands except that the lobes are many and interspersed with nulls.

With most antennas it's good to remember the old line from Western movies: "Reach for the sky, buster!" Or "stick 'em up! Higher!"

I use an 80M doublet fed at the center with open wire line. Each time I have raised the center or ends by a significant number of feet, the performance seems to improve. It's now flat with the center and ends at about 40 to 50 ft. depending on which side of my sloping lot you measure. There are a few feet of wire dropping vertically at each end. I can use it on any band from 80M to 10M.

I find that fine-tuning each aspect of the antenna is enjoyable in terms of the way it looks, works and stands up to the weather. I can't, however, assign any sort of percentage improvement to my achievements.

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AC6CV
Member

Posts: 256




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« Reply #11 on: April 30, 2016, 05:28:11 PM »

It is true the original Windom  had a single feed line and the OCF is the New Carolina Windom.  K4IWL is the one I patterned mine after. The OCF Windom cut for 40 meters on K4IWL web site works well in the inverted V configuration. Using calculations I made one for 80 meters. (4:1 current balun) I droop the ends down like an inverted V. However,  on the same mast tied to a separate 1:1 balun I have a 40 meter inverted V. Surprising to me on 40 meters the inverted V works better than the OCF. I still use the 40 meter cut OCF for portable use. I am going to remove the 80 meter OCF and replace it with a 40 & 80 meter inverted V tied to a 1:1 Balun. IMHO if I was limited in antennas I would put up an 80 meter inverted V (1:1 balun) and use a OCF cut for 40 meters on the same mast (4:1 balun)  in a inverted V configuration. Hard to beat an inverted V. Years ago on a city lot I had an inverted V mounted on my roof cut for every band except 80. Not enough room fo 80 meters. They were tied to the same balun and spaced around the mast. It worked very well.
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