On Sep 11, 2:04*pm, Art Unwin wrote:
On Sep 10, 10:56*pm, wrote:





On Sep 10, 10:29*pm, Art Unwin wrote:

On Sep 10, 9:23*pm, Art Unwin wrote:

On Sep 10, 8:45*pm, wrote:

Art Unwin wrote:
What is the main factor that prevents HF radiation from focussing
for extra gain?

Money.

If you can afford to build a 20m parabola about 2,000 feet in diameter
and the place to mount it, you'll get lots of gain.

--
Jim Pennino

Remove .spam.sux to reply.

Then are you saying it is the antenna size that is the main factor?..
So my antenna which is physically small
can be focussed on a dish which would provide straight line radiation
or a radiation beam?
Working on a single element on the ground with a optimizer instead of
a half sphere I got a
straight vertical line at the sides which suggested a gun barrel
radiation with a perfect earth as the reflector.
Gain was around 8db vertical which is why the question regarding
focussing! If it was properly focussed the gain should be more.
2000 foot dish seems somewhat odd, probably based on a "straight"
wavelength and not a small volume in equilibriumas the directer
right?
Art

Let me ask the question another way. Whether it is believed or not,
if a 80 Metre antenna was compressed to the size of a couple of shoe
boxes
would the dish be reduced in size accordingly?
Regagards
Art- Hide quoted text -

- Show quoted text -

No. The shoebox size antenna would approximate an isotropic if it did
radiate. It would still have to be placed at the focal point of a very
large parabola due to the size of the wave length. Such an antenna, I
believe, on the island of Puerto Rico (the SETI antenna) although it
is currently used primarily as a receiving antenna. That parabola is
positioned to have a very high radiation angle and might not be be
that good for terrestrial DX.

The antenna at PR has a stable reflector and a moveable receiver
thus the take off angle depends on the angular position of the
receiver
and the center of the reflector. The receiver is moved regularly so
the
sky can be traversed for listening. This was the idea when the antenna
*was set up initialy by Princeton University before they gave up
possesion of it.
With respect to WL no facts have been presented to support that fact.
If you go back to the arbitrary border analysis a force thru the paper
of the center
of the border will present resultant forces around the outside of the
border representing
ripples on water in wave like fashion, that does not correlate to the
ejection
*of a particle thru a fissure in the border. Mixing apples and oranges
no less
Nuf said- Hide quoted text -

- Show quoted text -

That is interesting. I thought the PR dish was parabolic. As a
parabola, the reflected waves (or particles if you will) of a
transmitter at focal point can only traverse in one direction, that
is, in a direction parallel to the tangent of a line drawn at the
lowest point of the parabola. If the parabolic reflector is
stationary, how can transmitted waves/particles go in any direction
but straight up in that perpendiculr direction? If you move the focal
point as you say they do, then the antenna does not finction as
parabola anymore and gain should drop drastically, agree? I am afraid
I must be missing something and request your technical advice. Thanks.

wrote:

That is interesting. I thought the PR dish was parabolic. As a
parabola, the reflected waves (or particles if you will) of a
transmitter at focal point can only traverse in one direction, that
is, in a direction parallel to the tangent of a line drawn at the
lowest point of the parabola. If the parabolic reflector is
stationary, how can transmitted waves/particles go in any direction
but straight up in that perpendiculr direction? If you move the focal
point as you say they do, then the antenna does not finction as
parabola anymore and gain should drop drastically, agree? I am afraid
I must be missing something and request your technical advice. Thanks.

The Arecibo radio telescope has a spherical reflector, not parabolic.
This is mentioned on the official web page:

http://www.naic.edu/public/the_telescope.htm

It also gives details on how the telescope operates.

--
Mark Cudworth

I am running the numbers on several 10 meter OWA 6 element antennas
with boom lengths of 24 to 26 ft. Tools on hand are "Yagi Analyzer",
"Yagi for Windows" by Dean Straw, and the spreadsheets by W6NL.
Several designs look promising, but I've gotten myself confused about
how to correctly model the clamps. The official Hygain YO files from
Roger Cox are not consistant as to equivalent diameter or length in
comparing the 203BA, 204BA, and the 205CA.
"What's the problem?" you say. Well, I'd like to use the inboard
sections of some 204BA elements for the driven element and the first,
close-spaced director.
An email to ARRL Technical Services was not enlightening, and
re-reading Jim Lawson's and Dave Leeson's works did not give me that
warm, confidant feeling that I'd like.
Anyone care to enlighten me with actual numbers, or websites??
Gud Lk in the contest!

Mike W5CHR
Memphis Tenn

On Fri, 12 Sep 2008 01:12:13 -0500, "Mike Lucas"
wrote:

"What's the problem?" you say. Well, I'd like to use the inboard
sections of some 204BA elements for the driven element and the first,
close-spaced director.

Hi Mike,

I would say "have at it," but what has this got to do with clamps?

They cannot present any perturbation to the calculations that wouldn't
be lost in the fourth right most digit after the decimal point. Even
more un-compelling, modeling probably wouldn't get you any closer to
reality than the second right most digit after the decimal point.

There are too many confounding properties of earth, nearby objects,
and the usual variability in materials and construction to imagine you
are going to both model and build one right out of the box, so to
speak.

On the other hand, actually setting your mind to it and doing it is
merely a matter of planning and performance right down to the size of
the clamp nuts. This is nothing more than a geometrical description
using wire sections of various diameters. The clamp is a half turn of
a loop of a certain wire diameter, and the nut is merely a wider wire
short section along the straight part of that half loop. Getting it
to wrap around an even thicker wire (the boom), and pierce thick wires
(the elements) will be a trick, and you will soon discover that you
have violated at least one rule of the MANA engine (about proximity
of, or overlapping segments). Myself, I would simply make the boom of
a series of sections, where the clamp area has a slightly greater
diameter.

This exercise is useful to do once for the drill. You get to learn
what counts and what does not, and then keep only those lessons that
actually offer something that lifts above the background noise of
mathematical error.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote:
Hi Mike,

I would say "have at it," but what has this got to do with clamps?

Richard: Tnx for the post- I enjoy slogging through the math to 4 places,
but then I usually round off to the nearest 1/16th when building something.
My brain had become numb from particals (sic) with spin, dripping from
tilted elements. I decided to restart a construction project, just on the
odd chance that I'll get it finished and on the tower before (if) the next
Solar Cycle happens. So why not some poetry or at least free verse
next time???

Mike W5CHR
Memphis Tenn

On Fri, 12 Sep 2008 11:33:02 -0500, "Mike Lucas"
wrote:

Richard: Tnx for the post- I enjoy slogging through the math to 4 places,

An occupation that pleases me too.

So why not some poetry or at least free verse next time???

Sorry Mike,

Tilting untennas is suggestive of the crusades of the Man of La Mancha
and particals (sic) with spin remind me of Singing in the Rain -
derivative humor at best here, which is improved by decanting only for
the ranting author. Examples abound.

However, you can rest assured that using a couple of three syllable
words in a sentence is bound to be hooted at as being lifted from
Shakespeare, or undecipherable trappings of a foreign language. The
hayseed mentality is fairly distributed across the globe but we sure
get a unique crop cultivated here.

However, as I plunge into your suggestion, one quote comes to mind
from Herman Melville's "White Jacket":
"It is often observable, that, in vessels of all kinds,
the men who talk the most sailor lingo are the least
sailor-like in reality. You may sometimes hear even
marines jerk out more salt phrases than the Captain
of the Forecastle himself. On the other hand, when
not actively engaged in his vocation, you would take
the best specimen of a seaman for a landsman.
When you see a fellow yawning about the docks like
a homeward-bound Indiaman, a long Commodore's
pennant of black ribbon flying from his mast-
head, and fetching up at a grog-shop with a
slew of his hull, as if an Admiral were coming
alongside a three-decker in his barge;
you may put that man down for what
man-of-war's-men call a 'damn-my-eyes-tar',
that is, a humbug. And many damn-my-eyes hum-bugs
there are in this man-of-war world of ours."

73's
Richard Clark, KB7QHC

I have never built a yagi using Hygain elements, but I have built
some 6 element OWA's like you want to build. The effect of
the clamps will be larger than "4th digit", probably a couple of
inches at 28 MHz. But you can ssume to a very good approximation the clamp
will just shift the resonant freq of those elements by a certain amount.

When I built my OWA's I used DX engineering insulated element mounts. With
these, the SWR curve of the real antenna matched the tapered NEC2 model
perfectly. I didn't even need to adjust the length of the driven element.

If you were using a Hygain element for only the driven element, I would
just allow for a few inches of adjustment + or - (hose clamp on last segment),
and just adjust the tip length of the final antenna to get the correct
SWR curve. If you want to use Hygain elements for Dr and 1st Dir, just do
the same, but adjust the lengths of both Dr and 1stDir by the same amount.
In the OWA design changing the length of the Dr and 1st Dir is mostly
going to affect the matching of the antenna.

Tor
N4OGW

wrote
When I built my OWA's I used DX engineering insulated element mounts. With
these, the SWR curve of the real antenna matched the tapered NEC2 model
perfectly. I didn't even need to adjust the length of the driven element.


Tor:
Thanks for the reply. I've used home-brew plates and u-bolts for a
couple of
3 and 4 element 10M antennas, but all were grounded. The gamma match that
was
spit out by the YA program worked as calculated, and within the limits of
the equipment,
the measured VSWR curves matched the model.
While the subject line said "Hygain element clamps", I also have a box
full of Wilson
element clamps, both are close in appearance, but the Wilson clamps are
about
15-20% larger than the Hygain of the same element size.
First runs on an OWA for 10M used 3/4, 5/8, and 1/2 in. tubing, with a
bushing in the
element clamp to bring it down to 3/4 size. I was looking for flat gain and
F/B curves,
close to 50 Ohm feed, and use on-hand parts. I came up with a couple of
models that
looked promising, but I'm now looking at using 1-1/4 to 7/8 taper elements
for the driven
and first director. Since my optimizer is me, I haven't run enough samples
to tell if that will
show any improvement. What I have seen is that if a design is poor, a small
change in
taper schedule, element length or element spacing will make a noticeable
change in the
model characteristics, usually bad.
Plans are for a single 10M OWA here in Memphis, to be followed by a
3-high stack
at the retirement Ponderosa. I have also looked at scaling up to 20M, where
a 3 inch
boom prevents using the clamp style mounts. Sooo, thanks for the post, and
I'll
see you on the bands.

Mike W5CHR
Memphis Tenn

On Sep 12, 12:59*am, Mark Cudworth
wrote:
wrote:
That is interesting. I thought the PR dish was parabolic. As a
parabola, the reflected waves (or particles if you will) of a
transmitter at focal point can only traverse in one direction, that
is, in a direction parallel to the tangent of a line drawn at the
lowest point of the parabola. If the parabolic reflector is
stationary, how can transmitted waves/particles go in any direction
but straight up in that perpendiculr direction? If you move the focal
point as you say they do, then the antenna does not finction as
parabola anymore and gain should drop drastically, agree? I am afraid
I must be missing something and request your technical advice. Thanks.

The Arecibo radio telescope has a spherical reflector, not parabolic.
This is mentioned on the official web page:

* *http://www.naic.edu/public/the_telescope.htm

It also gives details on how the telescope operates.

--
Mark Cudworth

Thank you Mark. It truly is spherical.