On Wed, 07 Jul 2004 19:16:36 -0400, Albert wrote:

|OK, thanks Richard.
|
|How about this.
|
|30 wavelengths per side, average conducting ground, 12 feet above
|ground.
|
|What angle do I need for best forward gain, what will the takeoff
|angle be at that angle?

Included angle from 12 to 16 degrees will give ~20 dBi at 6 deg
elevation.
|
|If I can get the entire antenna up to 20 feet above ground, how much
|better is the performance?

~ 2 dB more gain at 4 deg el.
|
|Is there any way for me to do modelling myself without burdening you
|or someone with a modeling program? I am not aware of free software
|that will model rhombics or vee's.

4nec2 is free, do a Google search

Multinec is cheap and very flexible.

|
|Thanks,
|
|Art
|
|ky1k at pivot dot net
|
|PS: Some additional info. This is for EME, which does not require much
|movement. Since it is so long, it won't be variable in the elevation
|angle anyway. But, I hope to move one wire a bit so I can steer the
|beam to the left or to the right a little (changing the angle of the
|vee at the same time).

Since I worked VK5MC to complete my 2-meter WAC and he used a slightly
steerable rhombic, I'm not going to say that this won't work, but I
must question why. If you're going to limit yourself to a few minutes
of moon time a month, why not just put up a long fixed Yagi and use it
for both transmit and receive. A forty-foot long Yagi will give the
same gain as the vee, with a *huge* improvement in the pattern and it
will have a much more tractable feedpoint impedance.

Wes

On Thu, 08 Jul 2004 09:10:41 -0700, Wes wrote:

On Wed, 07 Jul 2004 19:16:36 -0400, Albert wrote:

|OK, thanks Richard.
|
|How about this.
|
|30 wavelengths per side, average conducting ground, 12 feet above
|ground.
|
|What angle do I need for best forward gain, what will the takeoff
|angle be at that angle?

Included angle from 12 to 16 degrees will give ~20 dBi at 6 deg
elevation.
|
|If I can get the entire antenna up to 20 feet above ground, how much
|better is the performance?

~ 2 dB more gain at 4 deg el.
|
|Is there any way for me to do modelling myself without burdening you
|or someone with a modeling program? I am not aware of free software
|that will model rhombics or vee's.

4nec2 is free, do a Google search

Multinec is cheap and very flexible.

|
|Thanks,
|
|Art
|
|ky1k at pivot dot net
|
|PS: Some additional info. This is for EME, which does not require much
|movement. Since it is so long, it won't be variable in the elevation
|angle anyway. But, I hope to move one wire a bit so I can steer the
|beam to the left or to the right a little (changing the angle of the
|vee at the same time).

Since I worked VK5MC to complete my 2-meter WAC and he used a slightly
steerable rhombic, I'm not going to say that this won't work, but I
must question why. If you're going to limit yourself to a few minutes
of moon time a month, why not just put up a long fixed Yagi and use it
for both transmit and receive. A forty-foot long Yagi will give the
same gain as the vee, with a *huge* improvement in the pattern and it
will have a much more tractable feedpoint impedance.

Wes

Hi Wes,

Thanks for the information, it's just what I needed.

I am not sure how dbd converts to dbi, but a 100 foot 43 element rope
yagi gives 19 dbd.

My motivation for starting this was that I had the room for a large V
beam and that it might be practical if I could get the same gain as
the big rope yagi.

The V beam is way easier to put up and much cheaper and simpler to
construct.

From looking at data from smaller rhombics, it appears they are poor
for receiving as they have some major lobes that point towards the
high noise temperature Earth, which is why I wanted the V for transmit
only. I don't think the radiation off the back of the antenna will do
any harm in transmit only, so my hope was that it does not need to be
terminated.

Your gain figures indicate this bears further investigation, even
though I would be dependent on moon set or moon rise to make my Q's.
But, people with yagis have had that limitation and live with it just
fine.

I'll look up 4nec2 and try to play with it myself. Hopefully, it will
handle large V's.

Regards,

A


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On Wed, 07 Jul 2004 17:44:58 -0400, Albert wrote:
How much gain (dbd) should I expect and about what take off angle will
I have?

Hi Al,

Contrary to Wes' results, I do not find much more than 13dBi, and
certainly not from your proposed huge implementation running out
towards 50 wavelengths. In fact, I find antennas that are a tenth of
that (5M) have about as much gain as will be found.

My matrix of testing shows that doubling to 10 wavelengths and
doubling again to 20 wavelengths brings no further gain (except for
some opportunistic outliers).

As a variation upon a theme, I decided to play with uptilt on the 5
wavelength models, lifting the far ends by roughly 25 degrees. The
feed point is at 3M, and the far ends are lifted 5M. With this
configuration, there is some loss in gain, but the lobe looking at the
horizon is easily four times broader. That is, there is an even gain
of roughly 11dBi from 14 degrees above the horizon to 34 degrees above
the horizon. This occurs for the tips being separated by 30 to 90
degrees (the gain falls to 9dBi with wider separation).

When you separate further, out at 150 degrees between the tips, the
broad characteristic collapse, but recaptures gain, and puts it out
lower. At such a configuration you might observe 11dBi @ 4 degrees.
That lobe is only 3 or 4 degrees tall however.

Considering that common implementations of rhombics rarely go beyond a
couple of wavelengths to several, it seems that 20 or 40 or 50 has no
future. The law of diminish returns must occur somewhere as you are
constantly losing power as it trucks down the length. At that far
end, nothing added to little before it hardly piles up gain.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Wed, 07 Jul 2004 17:44:58 -0400, Albert wrote:
How much gain (dbd) should I expect and about what take off angle will
I have?


Contrary to Wes' results, I do not find much more than 13dBi, and
certainly not from your proposed huge implementation running out
towards 50 wavelengths. In fact, I find antennas that are a tenth of
that (5M) have about as much gain as will be found.

My matrix of testing shows that doubling to 10 wavelengths and
doubling again to 20 wavelengths brings no further gain (except for
some opportunistic outliers).

[...]
Considering that common implementations of rhombics rarely go beyond a
couple of wavelengths to several, it seems that 20 or 40 or 50 has no
future.

Those findings of "no further gain" and "no future" are very strange. In
the real world, extreme-length rhombics on VHF do have high gain - and
also a very distinguished past.


The law of diminish returns must occur somewhere as you are
constantly losing power as it trucks down the length.

All types of antenna suffer from diminishing returns, in terms of gain
versus absolute size; and it is conceded that extreme-length V-beams and
rhombics take up a huge amount of real estate for the gain they
generate. But what you seem to be finding is a "gain saturation" effect
that is more severe than the normal diminishing returns.

This is a puzzle: would you care to share some antenna files?


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

On Sun, 11 Jul 2004 10:49:30 +0100, "Ian White, G3SEK"
wrote:

This is a puzzle: would you care to share some antenna files?

Hi Ian,

That currently runs to 62 files, some EZNEC+4 - give me something you
are familiar with.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Sun, 11 Jul 2004 10:49:30 +0100, "Ian White, G3SEK"
wrote:

This is a puzzle: would you care to share some antenna files?

Hi Ian,

That currently runs to 62 files, some EZNEC+4 - give me something you
are familiar with.

I have EZNEC+ v4 too, but that is the only format I can presently read.
Please can you zip and send a selection of files that seem to illustrate
the point?


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

On Sun, 11 Jul 2004 07:53:54 GMT, Richard Clark
wrote:

On Wed, 07 Jul 2004 17:44:58 -0400, Albert wrote:
How much gain (dbd) should I expect and about what take off angle will
I have?

Hi Al,

Contrary to Wes' results, I do not find much more than 13dBi, and
certainly not from your proposed huge implementation running out
towards 50 wavelengths. In fact, I find antennas that are a tenth of
that (5M) have about as much gain as will be found.

My matrix of testing shows that doubling to 10 wavelengths and
doubling again to 20 wavelengths brings no further gain (except for
some opportunistic outliers).

As a variation upon a theme, I decided to play with uptilt on the 5
wavelength models, lifting the far ends by roughly 25 degrees. The
feed point is at 3M, and the far ends are lifted 5M. With this
configuration, there is some loss in gain, but the lobe looking at the
horizon is easily four times broader. That is, there is an even gain
of roughly 11dBi from 14 degrees above the horizon to 34 degrees above
the horizon. This occurs for the tips being separated by 30 to 90
degrees (the gain falls to 9dBi with wider separation).

When you separate further, out at 150 degrees between the tips, the
broad characteristic collapse, but recaptures gain, and puts it out
lower. At such a configuration you might observe 11dBi @ 4 degrees.
That lobe is only 3 or 4 degrees tall however.

Considering that common implementations of rhombics rarely go beyond a
couple of wavelengths to several, it seems that 20 or 40 or 50 has no
future. The law of diminish returns must occur somewhere as you are
constantly losing power as it trucks down the length. At that far
end, nothing added to little before it hardly piles up gain.

73's
Richard Clark, KB7QHC

Hi All,

Following up with a series of 2 wavelength measurements, it is
interesting to note that of the series of 19 tests, fully 13 of them
evidenced HIGHER gain than those from the 20 wavelength series of
measurements.

The step from 2 wavelength to 5 wavelength showed gains consistent
with doubling the length of the antenna size for many separations
(e.g. 3dB gain, or thereabout). However, it appears that beyond 5
wavelengths (considering my next cardinal point was a doubling to 10
wavelengths) no further gain was observed as a general characteristic.

If I were to judge this at the 180 degree spread and compare against
ALL other designs; then the absolute greatest gain for a V design was
observed to be slightly less than 4dB. In fact, the 2, 5, 10, and 20
wavelength designs configured as simple dipoles barely differed one
from the other (1dB at most, and typically 9.9dBi).

73's
Richard Clark, KB7QHC

Richard Clark wrote:
The step from 2 wavelength to 5 wavelength showed gains consistent
with doubling the length of the antenna size for many separations
(e.g. 3dB gain, or thereabout). However, it appears that beyond 5
wavelengths (considering my next cardinal point was a doubling to 10
wavelengths) no further gain was observed as a general characteristic.

Was this for a copper wire antenna? What happens when you choose
wire loss = zero?
--
73, Cecil http://www.qsl.net/w5dxp



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On Mon, 12 Jul 2004 07:31:01 GMT, Richard Clark
wrote:
[Earlier stuff snipped]
|
|Following up with a series of 2 wavelength measurements, it is
|interesting to note that of the series of 19 tests, fully 13 of them
|evidenced HIGHER gain than those from the 20 wavelength series of
|measurements.
|
|The step from 2 wavelength to 5 wavelength showed gains consistent
|with doubling the length of the antenna size for many separations
|(e.g. 3dB gain, or thereabout). However, it appears that beyond 5
|wavelengths (considering my next cardinal point was a doubling to 10
|wavelengths) no further gain was observed as a general characteristic.
|
|If I were to judge this at the 180 degree spread and compare against
|ALL other designs; then the absolute greatest gain for a V design was
|observed to be slightly less than 4dB. In fact, the 2, 5, 10, and 20
|wavelength designs configured as simple dipoles barely differed one
|from the other (1dB at most, and typically 9.9dBi).


I must confess that I've tried to follow your path but clearly I'm
lost.

May I suggest that analysis at "180 degree spread", which I take to
mean a dipole, has no relationship to a vee configuration, other than
the wire length. If you will take each leg length and vary the apex
angle to the optimum, you will (should) find that the gain *does*
continue to increase with increased leg length, albeit at a
sub-proportional rate.

For each leg length there is an optimal apex angle. Leaving the angle
fixed and varying the length is *not* a fair test of gain vs. length.

Here are the results I obtained from a quick MultiNEC (NEC-2)
analysis. This at 144 Mhz with height = 20', Sommerfeld Gnd, with
average dirt. #12 AWG Al wire, 20 segments/WL, elevation angle = 4
deg. Source on the middle of a short (3 segment) wire.

Len. (WL) Ang. (deg) Gain (dBi)

10.200 30 19.84
20.193 20 21.97
30.188 16 23.06
40.185 14 23.70
50.182 12 24.10

These data seem resonable and consistant with my expectations.

Wes

On Mon, 12 Jul 2004 10:24:01 -0700, Wes wrote:

Here are the results I obtained from a quick MultiNEC (NEC-2)
analysis. This at 144 Mhz with height = 20', Sommerfeld Gnd, with
average dirt. #12 AWG Al wire, 20 segments/WL, elevation angle = 4
deg. Source on the middle of a short (3 segment) wire.

Len. (WL) Ang. (deg) Gain (dBi)

20.193 20 21.97

Hi Wes,

For this particular design (except mine is elevated 5 wavelengths), I
pushed for 1 degree resolution, with a split source, with tapered
segments (1023 all told) and I still fall short, but also well ahead
of my earlier reports:
18.5dBi @ 3 degrees w/3 degree lobe width

73's
Richard Clark, KB7QHC