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Author Topic: Hanging an OCF dipole / Windom?  (Read 3621 times)
WALTERB
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Posts: 528




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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: 13029




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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
Member

Posts: 528




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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
Member

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
Member

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
Member

Posts: 1619




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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: 141




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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
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