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Author Topic: Horizontal v beam w/ 102" whips.  (Read 5001 times)
K9SRV
Member

Posts: 121




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« on: December 20, 2011, 01:14:39 PM »

Hey guys, always enjoy your input re. antennas.
I have a new question. I built a 10 meter v beam
using trucker mounts. I have the v at just over 90
degrees.

Here is the question. I have the mounts on a wooden
pole so the antenna is radiating just off the 102 inch
stainless steel whips. Is this the way to go,or would I be better off
using a metal pole?

Thanks,
John
KB9ICO
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K1WJ
Member

Posts: 458




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« Reply #1 on: December 20, 2011, 02:49:39 PM »

A non conductive mast works best - wood is good.  Cool 73 K1WJ
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KJ4I
Member

Posts: 111




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« Reply #2 on: December 20, 2011, 02:53:01 PM »

Looks like those whips would move around in the wind too much and mess up the pattern but I don't know how bad. Then again it might not make much difference. Just a thought that occurred to me.
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WB6BYU
Member

Posts: 13341




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« Reply #3 on: December 20, 2011, 04:03:07 PM »

First, that isn't a vee beam, unless perhaps you are using it on 2m or higher.
For 10m it's just a bent dipole, and, regardless of what misguided articles you may
find on the internet, it won't work any better than a normal dipole.

But it should work OK as a 10m dipole, and it probably doesn't make any difference
whether you mount it on a metal or wood mast.
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K9SRV
Member

Posts: 121




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« Reply #4 on: December 21, 2011, 02:09:33 PM »

So you are saying that a 10 meter V Beam wiil have no directionality, different than a straight
dipole unless each leg is 40 feet or longer? Just trying to understand, because you are
right, I have read a lot on v beams on the net.

Thanks much,
John
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K1WJ
Member

Posts: 458




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« Reply #5 on: December 21, 2011, 02:31:18 PM »

A 10m dipole cut for 28.400mhz = 16.5ft - so each leg is 8.25ft+-.

Did not see pic of your v-beam - for it to be a beam it has to have more than just the driven element.

Standard 3 element beam would have a director element, driven & reflector element.

Director element is shorter, Reflector element is longer - than driven element.

MFJ makes a Dipole mount - that I have used 2 MFJ hamtenna's on - see reviews here on eham, could also use 2 102in whips -

102in whips would droop - but that is ok.

For 10m get antenna at least 16ft ( 1/2 wave +-) off the ground - you will be all set.

For next several months I would not expect alot of openings - but check daily - day time hours are best for 10m-17m.

73 from Sunny Arizona K1WJ  Cool
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WB6BYU
Member

Posts: 13341




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« Reply #6 on: December 21, 2011, 02:45:06 PM »

Well, perhaps not quite 40 feet, but each side would need to be at least 1 wavelength long.
So 10 meters anyway, which is about 33 feet.  Generally, 3 to 6 wavelengths is more typical,
so 100 to 200 feet.  I have a wire vee-beam that I use for Field Day sometimes that is
185' on a leg.

You can get a bit of gain and directivity out if it if each side is 3/4 wavelength, and that
may have been where a lot of the misunderstandings came from:   many TV antennas have
vee-shaped elements because it gives a bit more gain on the third harmonic (channels 7 - 13)
of the elements cut for the lower channels 2 though 6.  I've seen a number of source that
apparently have interpreted this to assume that the basic half wave element shows gain
when bent 90 degrees, which certainly is NOT the case.


Unfortunately there are a lot of antenna articles on the internet that are not technically
competent, correct and/or coherent.  A good place to start your antenna research is the
site of the late L. B. Cebik, W4RNL.  You have to register (for free), but it has a wealth of
antenna information.  Much of it might be a bit complex for a beginner, but you will learn a
lot from browsing his articles on a wide variety of topics.  (And spend days doing it.)Here,
for example, are two articles that relate to your specific question:

http://www.cebik.com/content/a10/ant46.html
http://www.cebik.com/content/lpda/v1.pdf
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K9SRV
Member

Posts: 121




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« Reply #7 on: December 21, 2011, 06:12:18 PM »

Thanks! Its bookmarked!
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W2RSA
Member

Posts: 17




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« Reply #8 on: January 04, 2012, 04:03:12 PM »

I use two 5'6" francis whips and a mfj 945e here at my camper and they work well 15-6 meters
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W8JI
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Posts: 9296


WWW

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« Reply #9 on: January 04, 2012, 05:19:40 PM »

Hey guys, always enjoy your input re. antennas.
I have a new question. I built a 10 meter v beam
using trucker mounts. I have the v at just over 90
degrees.

John,

You must have been reading the V beam rubbish on Ham Universe.  :-) They have some nonsense about a V in two 1/4 wave antennas making a 3 dB gain beam.

If you take two 1/4 wave elements, like a dipole, and V them horizontally, the gain goes down...not up. 

It is very difficult to get more than a few dB gain with a V-beam, and to do that the legs have to be several wavelengths long with proper angle to align the lobes. 

I looked at V beams here for 80 and 40, and never found anything worthwhile. I never did find a combination that would make over a few dBd gain, and this was with hundreds of feet height and hundreds of feet of length. If anyone knows of a combination, please let me know leg length, height, and angle!!

73 Tom





 
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W5DXP
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Posts: 3621


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« Reply #10 on: January 04, 2012, 06:11:09 PM »

If anyone knows of a combination, please let me know leg length, height, and angle!!

Quoting from Antennas, by Kraus, 3rd edition, page 587: "By arranging two such 2WL wires in a V with an included angle of 72 deg ...", the associated radiation pattern is bidirectional with ~20 degree beamwidths. That should be easy to model with EZNEC.
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
W8JI
Member

Posts: 9296


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« Reply #11 on: January 04, 2012, 06:56:37 PM »

If anyone knows of a combination, please let me know leg length, height, and angle!!

Quoting from Antennas, by Kraus, 3rd edition, page 587: "By arranging two such 2WL wires in a V with an included angle of 72 deg ...", the associated radiation pattern is bidirectional with ~20 degree beamwidths. That should be easy to model with EZNEC.

At 160 feet high on 40 meters, 280 feet per leg, 13.2 dBi (about 5 dBd gain) and poor pattern. Beamwidth is ~20 degrees, but minor lobes are only -6 dB. Most of the azimuth area is -10 dB maximum, with a few nulls reaching -15 dB peak.

At 85 feet high on 40, same antenna, 12 dBi (about 3.8 dBd gain) and poor pattern.

My 3 element Yagi on a 50 foot boom has almost 3 dB more gain at 85 feet high.

This is with 8 ga copper elements.

This is a disappointing antenna.
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K0ZN
Member

Posts: 1553




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« Reply #12 on: January 04, 2012, 09:21:15 PM »


Hi, John....

Just to "add" to the above comments:  With two 102" whips, the best (i.e. best radiation efficiency) thing you could do is to have them 180 degrees
apart in a DIPOLE configuration.  It would defy the laws of electrical physics to get true, real "gain" with two quarter wave elements. The BEST you can do
is get 100% radiation efficiency in a rotatable dipole with those two whips.

Once the angle between two dipole elements goes under 90 degrees (i.e. the "V" angle becomes less than 90 deg.) you start getting CANCELLATION of the
radiation between the two elements. As you bring them closer and closer, narrowing the angle of the V to the point both elements are parallel, you have
a transmission line with ZERO radiation!

As the previous posters noted: a REAL "V-beam" is a true long wire array that is hundreds of feet on a leg if you want significant gain.  The MARS station I
was involved with "back in the day" on an Army base had V beam pointed at Southeast Asia for phone patch traffic. It was a fairly narrow angle V, and was
~600+ ft. per side (that is 9 Wave Lengths on 20 M !) strung on telephone poles and it worked well. The interesting thing about a large long wire array is that they show significantly reduced fading due to the large space diversity. You won't see anything like that with two 8 ft. whips in a V configuration.

Respectfully, pick up a copy of the ARRL Antenna Book and put in a little time on antenna fundamentals. They are not complex and the knowledge you pick
up will give you a better signal, reduced problems and the ability to spot B$ articles and advertisements about antennas! You can pick up an older copy of
the ARRL Antenna Book on Ebay cheap and the basic theory info in it is still correct as a new one.

73,  K0ZN
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WX7G
Member

Posts: 6136




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« Reply #13 on: January 05, 2012, 04:26:49 AM »

The metal pole vs. wooden does not matter since the coaxial cable routed along a wooden pole would be the same.
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W5DXP
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Posts: 3621


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« Reply #14 on: January 05, 2012, 05:24:33 AM »

This is a disappointing antenna.

Well, maybe you will like this one better - again from the same reference: "... a V antenna consisting of two cylindrical conductors 1.25WL long and 1WL/20 diameter with an included angle (beta) of 90 deg has the highly unidirectional pattern of Fig. 16-50d."

On 160m, the diameter of the conductor would be only 26 feet or so.Smiley
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
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