V Beam, do they work?
w8...@akorn.net
can seem to get one that has useful gain.
Has anyone seen a successful model anyplace of a two or three wave V
with good gain??
73 Tom
Dale Parfitt
<w8...@akorn.net> wrote in message
news:1143078002.7...@g10g2000cwb.googlegroups.com...
I have a model of a 5 wavelength 24MHz Vee beam in AO- I can send the file
if it is useful to you. AO reports 11dBi free space gain. Included angle
appears to be 44 degrees.
Dale W4OP
w8...@akorn.net
I don't have AO Dave, so a description will work.
That sounds like the problem I am seeing. With a 3-5 WL long V, I have
about the same gain as a three element Yagi. But I'll still try to
model your antenna with 5wl legs and 44 degree angle. Thanks.
Dale Parfitt
<w8...@akorn.net> wrote in message
news:1143112714.3...@t31g2000cwb.googlegroups.com...
This is from the AO library:
F=24.94
The vertex is at the origin: 0,0
X,Y of 1st leg is 185.44', -74.92' #12 wire
X,Y of 2nd leg is 185.44', 74.92' #12 wire
Fed at the origin and modeled in free space
AO reports
Z= 255- J706
Forward gain= 11.34dBi
F/B 2.70dB
Hope this is useful,
Dale W4OP
Wes Stewart
Tom,
Some questions.
What is "good" gain?
What frequency?
How high?
Try this at 10 MHz. Dimensions in feet.
End 1 End 2
X Y Z X Y Z
W1 0.0 0.0 100.0 245.0 -114.2 100.0
W2 0.0 0.0 100.0 245.0 114.2 100.0
w8...@akorn.net
explain a bit...
> What is "good" gain?
More than a 3 element yagi.
> What frequency?
Well, I was trying 160, 80 and 40. I have a 300ft support at one
point, and a bunch of 100ft trees a good distance away across open
fields (maybe 800 feet).
> How high?
Anything up to 300 ft at the feedpoint.
> Try this at 10 MHz. Dimensions in feet.
That antenna almost equals a three element yagi in gain, but the 3 ele
yagi has a HPBW of 60 degrees. The V beam has a HPBW of 18 degrees. Not
so good. Even if I try two V beams, one inside the other, I can only
get 3dB more gain.
I was wondering if I was missing something, because I keep hearing
stories about how good big V beams work.
Dave
SNIPPED
>
> That antenna almost equals a three element yagi in gain, but the 3 ele
> yagi has a HPBW of 60 degrees. The V beam has a HPBW of 18 degrees. Not
> so good. Even if I try two V beams, one inside the other, I can only
> get 3dB more gain.
>
> I was wondering if I was missing something, because I keep hearing
> stories about how good big V beams work.
>
Something does not make sense!!
There HAS to be a difference in gain between two antennas IF their HPBW
are different. Isn't it the case that the narrower beam has to have
higher gain?
w8...@akorn.net
Dave wrote:
> Something does not make sense!!
>
> There HAS to be a difference in gain between two antennas IF their HPBW
> are different. Isn't it the case that the narrower beam has to have
> higher gain?
No.
First problem, the V beam has more loss. Probably because of the very
long current path through conductors.
Second problem, large sidelobes that rob power
The beamwidth of high gain is much narrower than a Yagi, but the thing
has no more gain.
It looks like a simple antenna, has a good reputation, but it doesn't
look very useful for anything. Unless there is a combination I'm
missing.
73 Tom
Dale Parfitt
<w8...@akorn.net> wrote in message
news:1143207103.8...@j33g2000cwa.googlegroups.com...
>
> Dave wrote:
>> Something does not make sense!!
>>
>> There HAS to be a difference in gain between two antennas IF their HPBW
>> are different. Isn't it the case that the narrower beam has to have
>> higher gain?
>
> No.
>
> First problem, the V beam has more loss. Probably because of the very
> long current path through conductors.
>
> Second problem, large sidelobes that rob power
>
>is almost as large as the main lobe, being typically only 2-3dB down from
>the forward lobe.
Dale W4OP
Buck
I was just reading about them in the antenna handbook. The v-beam is
better than a dipole and is directional, but the same wire bent
half-way out to make a rombic seems to add more gain. you might look
into it.
Buck
N4PGW
On 22 Mar 2006 17:40:02 -0800, w8...@akorn.net wrote:
--
73 for now
Buck
N4PGW
Dave
SNIPPED
>
> It looks like a simple antenna, has a good reputation, but it doesn't
> look very useful for anything. Unless there is a combination I'm
> missing.
>
> 73 Tom
>
I've never worked with a Vee antenna. But, while stationed at Hill AFB,
Utah we used two of them back to back to make a Rhombic :-) to support
the South East Asia phone patch nets during the Vietnam conflict. Fixed
point to point communication [We had an LP that was used for stateside
COMMs]
My understanding is that a narrow beam is formed along the axis
[centerline] of the Vee. In a standing wave antenna, the beam is
bi-directional. In a terminated antenna, traveling wave, the pattern is
unidirectional. The narrow beam width reduces interference from
undesired directions.
Total wavelength and included angle have significant impact on performance.
I wonder of Roy can add constructively to this discussion regarding
apparent low gain.
Wes Stewart
>w8...@akorn.net wrote:
>
>SNIPPED
>>
>> It looks like a simple antenna, has a good reputation, but it doesn't
>> look very useful for anything. Unless there is a combination I'm
>> missing.
>>
>> 73 Tom
>>
>
>I've never worked with a Vee antenna. But, while stationed at Hill AFB,
>Utah we used two of them back to back to make a Rhombic :-) to support
>the South East Asia phone patch nets during the Vietnam conflict. Fixed
>point to point communication [We had an LP that was used for stateside
>COMMs]
>
>My understanding is that a narrow beam is formed along the axis
>[centerline] of the Vee. In a standing wave antenna, the beam is
>bi-directional. In a terminated antenna, traveling wave, the pattern is
>unidirectional. The narrow beam width reduces interference from
>undesired directions.
Tom is correct. Vee beams and rhombics have horrible sidelobes that
make them in my estimation highly overrated. The vee is not completely
bi-directional, a couple of dB FB is not uncommon. A vee, just like a
rhombic can be terminated to increase the FB. If the legs are long
enough it -is- a traveling-wave antenna and is somewhat
self-terminating.
The claim for broadband gain is also suspect. There are optimum
parameters that are not frequency independent
Of course I can't fault VK5MC's three-stack rhombic that gave me my
two-meter WAC :-)
>
>Total wavelength and included angle have significant impact on performance.
Of course.
J. Mc Laughlin
It appears that you are investigating a slopping, V-beam with a feed point
at about 90 meters and an operating frequency of, say, 1.82 MHz. When first
used some 80 years ago, V-beams were horizontal (or, alternatively, entirely
in a vertical plane). Two more 90 meter poles are not likely to be in the
picture.
The good news is that you are apparently interested in a narrow range of
frequencies. That is good news because aligning the lobes with their
changing polarization and orientation over a significant bandwidth is like
composing something to compete with Mozart.
Even using one frequency, it is a bear to get a slopping V to do one's
bidding. I would limit lengths to integer multiples of 0.5L that could fit
your farm. I would optimize a single, end fed wire (over ground) and in the
process find a narrow range of lengths that look promising and that fit your
site. Then add, and drive, the second wire. Iteration is called for. I
would use a figure of merit that is the gain at a TOA of something like 30
degrees.
Kraus, even in the first edition, presents several approximate equations
to optimize a horizontal rhombic. They may give a little guidance. I think
I read a Technical Report in the mid 60s on measurements of a sloping V put
out by either NBS or ESSA. I seem not able to put my finger on it just now.
As mentioned, the difficulty with sloping wires is finding a "good"
bore-site addition of fields from the two wires when those fields are, to a
first approximation, in the shape of cones with changing polarization. It
is more easy with horizontal wires.
If I live long enough to retire from teaching, this is a type of project
that would be interesting to investigate. But I only have 42 years in and
my good wife is certain that I could not stand the pace of retirement. Do
let us know what you come up with. Good luck.
73, Mac N8TT
Two side notes: My friend, HS and University classmate, and great DXer
W8TWA has used a set of sloping V-beams on HF to good effect. -- As you know
better than almost anyone, one needs a height in the neighborhood of 2L to
get serious signals from a horizontally polarized antenna at the lower TOAs
used for DX. You may find that your best sloping V-beam has a strong
vertically polarized component in the main beam.