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Author Topic: inverted V mounting question - is it directional on the long leg  (Read 2622 times)
KF7NUA
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Posts: 153




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« on: February 27, 2012, 10:16:58 AM »

When raising a OCD and mounting it as an inverted  V, does it really matter which way the legs are pointed to or aligned to as in North South East West?
I am aware that inverted V mounted is more of a omni-directional antenna but I have also read on the internet more than once that OFC antennas are directional on the long leg.
I like to DX and living in Southern Arizona close to Mexico I am trying to figure out the easiest or better path to Europe.

73 Nick
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WB6BYU
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Posts: 13243




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« Reply #1 on: February 27, 2012, 11:03:45 AM »

That will depend on the wire length, frequency, slope of the wire, height above ground,
 and required vertical angle of radiation to reach the area of interest, among other things. 

If a long wire is sloping down too steeply it will perform poorly.  Especially when you are
using a 80m antenna above 20m, you may find that a half wave inverted vee at the same
top height outperforms a longer wire antenna.

This articles shows some plots, but doesn't directly answer your question:

http://www.cebik.com/content/a10/wire/vang.html
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KF7NUA
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Posts: 153




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« Reply #2 on: February 27, 2012, 11:24:09 AM »

thank you, I guess I should have included more info.

OFC 10 20 40m
66 or 67ft cant remember
about 23ft and 44ft legs
will be mounted about 28-30 ft high
I can mount the leg angles just about anywhere needed

does this info help?
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WX7G
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Posts: 6039




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« Reply #3 on: February 27, 2012, 11:35:33 AM »

An OCF properly fed has the exact same radiation pattern as the same wire center fed. By properly fed I mean no feed line common-mode current.
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WB6BYU
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Posts: 13243




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« Reply #4 on: February 27, 2012, 01:24:42 PM »

That's true on the fundamental (40m in this case) but not on the harmonics.

A center-fed 67' wire  on 20m will be two half waves in phase with maximum radiation
broadside to the wire.  The same wire fed off-center will be be two half waves
OUT OF PHASE and have a null broadside to the wire, with maximum radiation
at roughly 45 degrees to the wire. 

That's why a 80m OCFD doesn't work well for NVIS propagation on 40m, because
the pattern has a null overhead.


I can't answer the original question until I have a chance to sit down and model it.
There may be some cases where that is the case, but I doubt it holds up as a
general rule.  Certainly on 40m I'd expect more radiation broadside to the antenna.
On the higher bands I expect it will depend on the elevation angle you are looking at.
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KQ6Q
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Posts: 976




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« Reply #5 on: February 27, 2012, 02:23:26 PM »

If you've got the space, a 3/2 wave dipole for 20m is about 45 feet on a side, and tends to be directional toward the ends of the wires.
I had one set up with the center at the roofline of a 3 story building, with the ends drooping somewhat and tied off to stairwells projecting out from the same side of the building. The building faced north, and one leg gave me coverage to Europe, the other to the US.... I was HS2AJG at the time - fed the antenna with RG-11U, ran an Eico 753. I never had any trouble getting an answer to a CQ!
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KF7NUA
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Posts: 153




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« Reply #6 on: February 28, 2012, 07:28:39 AM »

Dont loose me guys, I am over 60yrs old and I became a ham operator less than a yr ago so I am not well versed in it as of yet.
I can say that I have built 4 wire antennas, all of them were multi band end fed that worked ok but not the greatest.
I decided to buy an OCD to try and here I am.

My thoughts are to place the angle of the legs at 120deg or close to it, is that too wide or close?
I was also going to place them in a East to West direction so North and South is broadside, is this a good idea for the QTH of Southern Arizona?
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WB6BYU
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Posts: 13243




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« Reply #7 on: February 28, 2012, 08:45:06 AM »

Quote from: KF7NUA

Dont loose me guys...



Sorry, but it really is not as simple of a question as it sounds.  The radiation pattern is
three-dimensional, and will be different on each bad due to how the currents are
distributed on the wires.  The three-dimensional nature means that, since contacts
over different distances require the antenna to radiate at different vertical angles
above ground, the directional properties will be different if the other station is 50,
500 or 2000 miles away.

40m is the simplest case:  the antenna radiation pattern is similar to a dipole.  In the
inverted vee configuration the overall pattern for shorter paths will be nearly
omnidirectional.  At somewhat further distances it will be a bit better broadside to the
antenna.  So the alignment isn't critical, but if you had a particular interest in working
New England or Alaska you could point it in that direction, but it might not make a lot
of difference.

If the antenna was horizontal, maximum radiation on 20m will be at roughly 40 degrees
to the line of the wire, with nulls broadside to the wire.  Sloping the wires changes it
somewhat, but also starts to fill in the broadside null.  The signal in the direction of the
long wire is slightly stronger, but not by a lot, but there is still more signal off the ends
than broadside to the wire.

On 10m the pattern has 8 lobes.  The relative strengths vary with the vertical angle, but
it is hard to say that any particular lobes are much stronger than the rest.  You'll get
somewhat stronger signals in some directions and weaker ones in others, but not any
large differences.


Quote

My thoughts are to place the angle of the legs at 120deg or close to it



Looking at the computer models, the best results are with the antenna as flat as possible.



Quote

I was also going to place them in a East to West direction so North and South is broadside, is this a good idea for the QTH of Southern Arizona?



That should cover most of the Western US on 40m, with some contacts further out. 

On 20m, putting the long wire to the East might be the best choice, as it would cover much
of the Eastern US.

On 10m you'll have contacts in many directions, and I don't think it matters much which way
you point it.
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KF7NUA
Member

Posts: 153




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« Reply #8 on: February 28, 2012, 11:35:24 AM »

Quote from: KF7NUA

Dont loose me guys...



If the antenna was horizontal, maximum radiation on 20m will be at roughly 40 degrees
to the line of the wire, with nulls broadside to the wire. 

Quote

My thoughts are to place the angle of the legs at 120deg or close to it



Looking at the computer models, the best results are with the antenna as flat as possible.



WB6 - Thank you I can follow everything you said exept these 2 things.
Are you saying that I should cancel the inverted V plan and go with flat as flat will be a big difference?
What does this mean
If the antenna was horizontal, maximum radiation on 20m will be at roughly 40 degrees
to the line of the wire?Huh Does this mean as a 20deg fan off the end of wire in both left and right direction?
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WB6BYU
Member

Posts: 13243




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« Reply #9 on: February 28, 2012, 11:54:38 AM »

Quote

Are you saying that I should cancel the inverted V plan and go with flat as flat will be a big difference?


It's not a big difference.  Probably not enough reason to put up extra supports instead of hanging
it off a lone tree.  Just tie the ends of the wires as high as practical - don't intentionally make the
angle any sharper than necessary.  That keeps the average height of the antenna as high as
possible, which generally is a good thing.  And it doesn't matter if the angle is the same on
both wires.



Quote

What does this mean
If the antenna was horizontal, maximum radiation on 20m will be at roughly 40 degrees
to the line of the wire?Huh Does this mean as a 20deg fan off the end of wire in both left and right direction?



If the wire runs North / South, maximum radiation on 20m would be at 40 degrees from North
(on either side) and at 40 degrees from South.  So nearly NE / NW / SW / SE, but slightly
closer to north and south.  You'll get basically the same directions from an East / West wire,
but slightly closer to East and West instead.

If you look at the radiation pattern in free space (without ground), there is actually a cone of
radiation all around the wire.  Not only will it be 40 degrees on the left and right sides of the wire,
but also up and down at the same angle.  If the wire were tilted 40 degrees, then the upper
part of the cone would be pointing at the horizon directly off the end of the wire.  Generally,
the more the wire is tilted, the closer the direction of maximum radiation comes to being off
the end of the wire.  Unfortunately the ground reflections in the real world make such low angle
radiation ineffective, which is why tilting the wire too much makes a poor antenna.

Similarly on 10m with a flat wire the lobes of maximum radiation are about 20 degrees either
side of the direction of the wire, with slightly smaller lobes at something like 65 or 70 degrees.
The exact direction and strength of these lobes vary with the height and slope of the wire.


For long wires (1 wavelength or more) it is generally true that maximum radiation is more towards
the ends of the wire than broadside to it, but not necessarily directly off the end.

And for the range of variations we're looking at here, there aren't a lot of large differences
between them.  Except for the broadside null on 20m - if the wire runs East / West you're
signal won't be very strong in Montana on 20m.
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KF7NUA
Member

Posts: 153




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« Reply #10 on: February 29, 2012, 07:19:22 AM »

Quote

Are you saying that I should cancel the inverted V plan and go with flat as flat will be a big difference?


It's not a big difference.  Probably not enough reason to put up extra supports instead of hanging
it off a lone tree.  Just tie the ends of the wires as high as practical - don't intentionally make the
angle any sharper than necessary.  That keeps the average height of the antenna as high as
possible, which generally is a good thing.  And it doesn't matter if the angle is the same on
both wires.



Quote

What does this mean
If the antenna was horizontal, maximum radiation on 20m will be at roughly 40 degrees
to the line of the wire?Huh Does this mean as a 20deg fan off the end of wire in both left and right direction?



If the wire runs North / South, maximum radiation on 20m would be at 40 degrees from North
(on either side) and at 40 degrees from South.  So nearly NE / NW / SW / SE, but slightly
closer to north and south.  You'll get basically the same directions from an East / West wire,
but slightly closer to East and West instead.

If you look at the radiation pattern in free space (without ground), there is actually a cone of
radiation all around the wire.  Not only will it be 40 degrees on the left and right sides of the wire,
but also up and down at the same angle.  If the wire were tilted 40 degrees, then the upper
part of the cone would be pointing at the horizon directly off the end of the wire.  Generally,
the more the wire is tilted, the closer the direction of maximum radiation comes to being off
the end of the wire.  Unfortunately the ground reflections in the real world make such low angle
radiation ineffective, which is why tilting the wire too much makes a poor antenna.

Similarly on 10m with a flat wire the lobes of maximum radiation are about 20 degrees either
side of the direction of the wire, with slightly smaller lobes at something like 65 or 70 degrees.
The exact direction and strength of these lobes vary with the height and slope of the wire.


For long wires (1 wavelength or more) it is generally true that maximum radiation is more towards
the ends of the wire than broadside to it, but not necessarily directly off the end.

And for the range of variations we're looking at here, there aren't a lot of large differences
between them.  Except for the broadside null on 20m - if the wire runs East / West you're
signal won't be very strong in Montana on 20m.

Thank you - this makes sense and I am not lost. I should have persued my ham license in 1959 when I was first introduced to then instead of doing it in 2011....
73 Nick
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WA9YSD
Member

Posts: 138




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« Reply #11 on: February 29, 2012, 12:26:11 PM »

I have been using inverted Vee s for many years now.

One time I had a Hustler vertical antenna mounted in the back yard with 8 tuned radials, a pair for each band.  Worked well but was not happy with it. So I built a 20 meter inverted vee and mounted it on the vertical. The inverted vee work much better.

Inverted vee in ideal situations is omni directional.

I never had an ideal situation. 40m and 80 meter inverted Vees ends never exceeded 20 feet above ground or structure.

Yes it still was omni direction.  Working deep DX the ends seams to do the job better than broad side.  Broad side worked better for shorter hops.  The best thing to do is to point the hot side of the inverted vee towards the area in the world you need to work seams to work best, is my belief.

On the other had propagation shifts around magnetic fields ground conductivity and the sort has proved me wrong and surprised me.

Jim K9TF
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