On Thu, 8 Jul 2004 09:33:45 -0400, "Tam/WB2TT"
wrote:

Hi Richard,
How about shooting for 112 Ohms, so he can match it with a 1/4 wave section
of RG11.

Tam/WB2TT

Hi Tam,

That would be an opening between 30° and 40° (106 to 122 Ohms) with a
gain around 12dBi (11.8 @10° to 11.9 @20°).

Impedance appears to change smoothly through out the full range; gain
and angle less so (but no more than this spread of 10°).

73's
Richard Clark, KB7QHC

Albert

I'm a little experienced with failure in trying EME on 2 meters. I'm not
a scientist, but have some information that might help you decide which
antenna is best for your situation.
I'm not able to calculate the amount of steering thats available with a
long V antenna. I couldn't even predict the antenna's radiation pattern
shape. If the antenna pattern has about equal beamwidth in both elevation
and azimuth, a 20 DB gain antenna will have about a 20 degree beamwidth (as
I remember).
You probably know all this, but--
The moon rises and sets at a slightly different azimuth each succeeding
day. The azimuth direction to the moon on the horizon might vary by about
50 degrees per year.
I consider the moon to be about 1/2 a degree wide. It will rise at "its
diameter" each 2 minutes.
It looks to me like you'd have a few minutes of 'max gain' each year, and
theres no way for you to predict _*when*_ because the "takeoff angle" at 2
lambda is unpredictable.
If my thinking about *where the moon is* is about right, I predict that
you wont be satisfied with an antenna that isnt more stearable than the V
for moon bounce.

I've read about a guy who made a long yagi antenna by suspending it on
ropes rather than 'booms'. I wonder if you might be more satisfied with a
yagi that you could "roll up" when icy weather approaches.

Jerry






"Albert" wrote in message
...


Hi Ian,

Thanks for your comments.

My hope was to use a v beam instead of a rhombic.

The V is relatively easy to steer, especially if the performance
doesn't change much if either leg is moved. Note that I hope to leave
one leg of the beam fixed and steer the az by varying the position
(and the V angle) of the other leg. Not sure how much changing the
angle of the V impacts the performance, which is why I asked for
someone with modeling software.

My hope was to exploit the high gain, simple construction (but poor
receive) of the V for transmit only and to use the modest sized FO
yagi for receive only.

If I can get 19 or 20 db from a big V beam, I can probably tollerate
the limited operating time as well, Q's with big guns should take only
minutes and medium sized stations should be workable in a 20 minute
window.

If the computer model predicts a usable gain, I'd like to try putting
one up.

Regards,

Art



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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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Albert

I can't help on the V any more than others, such as Richard, are, but I
can give you another cheap alternative that is as easy to repoint as
your V, maybe easier. VE7BQH published a rope beam for EME a while ago.
It is as cheap as rope and the elements plus TyWraps cost. The only
downside I can see is making the match, but that's not really too tough,
and you have to match to the V anyway. It will also have more gain than
the V would for the same real estate.

http://www.bigskyspaces.com/w7gj/longyagi.htm

tom
K0TAR

Albert wrote:

On Wed, 07 Jul 2004 19:14:03 -0500, Tom Ring
wrote:


Art

Which brand of EME is this for? If for one of the new digital modes,
you don't need that much gain, as you may already know. If it's for CW,
having a ton of gain in one direction only gives you a very seldom
available and very short window.



Thanks for the eme advice.

But, I was asking about the gain of a vee beam because they are cheap
to build and easy to put back up when the weather takes them out. We
have major ice storms often here.

Which "Brand of eme' is irreleveant, gain is gain regardless of which
mode is used. Excess gain is never wasted, it either makes the QSO
faster or allows one to work smaller stations or allows SSB instead of
CW/digital modes.

If the angle of the V makes little difference to the actaul gain, it
can be steered by moving either leg, which is also easy to do.

Although I can only work on my moon rise or moon set, more gain is
always better. Since I can't elevate my yagi, a non elevatable vee
beam for transmit only might give higher gain. The yagi would be for
receive only.

Having different receive and transmit antennas has benefits as well,
such as no switching loss and no need to protect my gaasfet during
transmit.

Can you offer any suggestions regarding the original question?

Thanks

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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