Parabolic Dish Questions
 

I have a Directv dish 35 inches wide x 20 inches tall 4inches deep.
I calculated the focus as F=D*2 / 16d where D =diameter and d=depth
F=18 inches Ok so far.
How do you find beamwidth? I think the 35" dimensiom would have a tighter
pattern than the 20 ", but how do you calculate,

Second, The feed antenna, There can be different feeds.
A simple monopole, dipole, biquad, patch, yagi, helix.
How does the feed antenna affect the gain of the dish, if at all?
Yea, it my be difficult to light the yagi or helix, so if you like throw
those out.
Thank You,
Mike

Parabolic Dish Questions
 

On Thu, 26 Jun 2008 07:35:31 -0500, "amdx" wrote:

I have a Directv dish 35 inches wide x 20 inches tall 4inches deep.
I calculated the focus as F=D*2 / 16d where D =diameter and d=depth
F=18 inches Ok so far.
How do you find beamwidth? I think the 35" dimensiom would have a tighter
pattern than the 20 ", but how do you calculate,

Second, The feed antenna, There can be different feeds.
A simple monopole, dipole, biquad, patch, yagi, helix.
How does the feed antenna affect the gain of the dish, if at all?
Yea, it my be difficult to light the yagi or helix, so if you like throw
those out.
Thank You,
Mike

You have a neat gadget here!
If you place a lamp (flashlight?) at the focus you can measure the
beam on a wall wth a tape measure.

Put a microphone at the focus and you can hear things you would not
believe...

Old ARRL antenna books, and authors like John Krause will be needed
to answer all of your questions.

John Ferrell W8CCW
Beware of the dopeler effect (pronounced dope-ler).
That's where bad ideas seem good if they come at you
fast enough.

Parabolic Dish Questions
 

"John Ferrell" wrote in message
...
On Thu, 26 Jun 2008 07:35:31 -0500, "amdx" wrote:

I have a Directv dish 35 inches wide x 20 inches tall 4inches deep.
I calculated the focus as F=D*2 / 16d where D =diameter and d=depth
F=18 inches Ok so far.
How do you find beamwidth? I think the 35" dimensiom would have a tighter
pattern than the 20 ", but how do you calculate,

Second, The feed antenna, There can be different feeds.
A simple monopole, dipole, biquad, patch, yagi, helix.
How does the feed antenna affect the gain of the dish, if at all?
Yea, it my be difficult to light the yagi or helix, so if you like throw
those out.
Thank You,
Mike

You have a neat gadget here!
If you place a lamp (flashlight?) at the focus you can measure the
beam on a wall wth a tape measure.

It grey, won't reflect light very well. Basically I wanted to know how the
beamwidth changed with the larger width dimension vs the smaller height
dimension

Put a microphone at the focus and you can hear things you would not
believe...

I already experienced the reflection. I had a radio playing on my right
side, I was moving the dish and got an increase in volume in my left ear. I
moved the dish back
to play around with the effect. Neat!

Old ARRL antenna books, and authors like John Krause will be needed
to answer all of your questions.

John Ferrell W8CCW
Beware of the dopeler effect (pronounced dope-ler).
That's where bad ideas seem good if they come at you
fast enough.

Parabolic Dish Questions
 

"amdx" wrote in message
...
I have a Directv dish 35 inches wide x 20 inches tall 4inches deep.
I calculated the focus as F=D*2 / 16d where D =diameter and d=depth
F=18 inches Ok so far.
How do you find beamwidth? I think the 35" dimensiom would have a tighter
pattern than the 20 ", but how do you calculate,

Second, The feed antenna, There can be different feeds.
A simple monopole, dipole, biquad, patch, yagi, helix.
How does the feed antenna affect the gain of the dish, if at all?
Yea, it my be difficult to light the yagi or helix, so if you like throw
those out.
Thank You,
Mike

The DirecTV dishes are not prime focus, bu rather offset. If it came with
the original horn mount, use it.
You can use:
http://www.w1ghz.cx/software/hdl_3b4.zip
to find the focal length,. Your formula assumes prime focus.

The gain of the dish is not a function of the feed, but the system gain is
because one must take into account surface illumination, feed efficiency
etc.

The subject of feeds for dishes is complex if you really want to optimize
G/T etc. Paul W1GHZ has a teriffic on-line text about parabolic surfaces and
feeds:
http://www.w1ghz.org/antbook/preface.htm

Dale W4OP

Parabolic Dish Questions
 

On 26 jun, 14:35, "amdx" wrote:
I have a Directv dish 35 inches wide x 20 inches tall 4inches deep.
I calculated the focus as F=D*2 / 16d where D =diameter and d=depth
F=18 inches Ok so far.
How do you find beamwidth? I think the 35" dimensiom would have a tighter
pattern than the 20 ", but how do you calculate,

Second, The feed antenna, There can be different feeds.
A simple monopole, dipole, biquad, patch, yagi, helix.
How does the feed antenna affect the gain of the dish, if at all?
Yea, it my be difficult to light the yagi or helix, so if you like throw
those out.
Thank You,
Mike

Hello Mike,

In case of uniform illumination, gain is maximum, side lobes are
maximum also and beam width is about 60*lambda/diameter (degrees).

You will certainly not reach this, for several reasons. The beam width
will be more, it can be twice as high (depending on the illuminator).

The maximum gain that you can obtain with a certain aperture antenna
is about 4*pi*A/lambda^2. In reality it will be less:

When you want uniform illumination, you will have "spill over" (part
of the radiated power will not reach the dish). To get most power onto
the dish, you must accept that the edges of the dish do receive less
power flux density.

In addition, the phase center of your illuminator will change versus
off-main beam direction. This causes phase differences so a non-planar
field. Also polarization may change for off-beam directions.

Other things are deviation from optimal parabolic shape, non correctly
positioned illuminator, etc. This will all reduce maximum gain.

Hope this helps a bit.

Best regards,

Wim
PA3DJS
www.tetech.nl

Parabolic Dish Questions
 

"amdx" wrote in message
...
I have a Directv dish 35 inches wide x 20 inches tall 4inches deep.
I calculated the focus as F=D*2 / 16d where D =diameter and d=depth
F=18 inches Ok so far.
How do you find beamwidth? I think the 35" dimensiom would have a tighter
pattern than the 20 ", but how do you calculate,

Thank You,
Mike

The DirecTV dishes are not prime focus, but rather offset. If it came with
the original horn mount, use it.

Yes, it is an offset feed and it did come with the mount and feed (LNA?)
Actually it came with two LNAs, but they didn't match each other. I don't
remember what junk pile this came from and don't have any info about it's
working condition.
I did measure the distance from the front of feed to the dish center and
it is 18" as calculated, however as I said I don't know if this worked as I
got it.

You can use:
http://www.w1ghz.cx/software/hdl_3b4.zip
to find the focal length,. Your formula assumes prime focus.

This link doesn't look right.

The gain of the dish is not a function of the feed, but the system gain is
because one must take into account surface illumination, feed efficiency
etc.

So I could use a biquad or patch as the feed antenna without much
difference?


The subject of feeds for dishes is complex if you really want to optimize
G/T etc. Paul W1GHZ has a teriffic on-line text about parabolic surfaces
and feeds:
http://www.w1ghz.org/antbook/preface.htm

Dale W4OP

I'll look at the w1ghz link.
I was suprised this dish is made of plastic. Does the EM wave reflect off
of the plastic or does the plastic have a coating?
Thanks, Mike

Parabolic Dish Questions
 

"Dale Parfitt" wrote in message
news:7xR8k.35$wR.10@trnddc07...

"amdx" wrote in message
...
I have a Directv dish 35 inches wide x 20 inches tall 4inches deep.
I calculated the focus as F=D*2 / 16d where D =diameter and d=depth
F=18 inches Ok so far.
How do you find beamwidth? I think the 35" dimension would have a tighter
pattern than the 20 ", but how do you calculate,

Second, The feed antenna, There can be different feeds.
A simple monopole, dipole, biquad, patch, yagi, helix.
How does the feed antenna affect the gain of the dish, if at all?
Yea, it my be difficult to light the yagi or helix, so if you like throw
those out.
Thank You,
Mike

The DirecTV dishes are not prime focus, bu rather offset. If it came with
the original horn mount, use it.

Hey I just found the dish I have it's at
http://www.solidsignal.com/satellite...enna_types.asp
Last dish on the right side of the page, it's called the International
Satellite Dish.
International 36". I note from the picture the feeds don't match, when I got
the dish
the position of the two feeds were reversed.
What can you glean fron this?
Thanks, Mike

Parabolic Dish Questions
 

amdx wrote:
"amdx" wrote in message
...
I have a Directv dish 35 inches wide x 20 inches tall 4inches deep.
=====================================
I was suprised this dish is made of plastic. Does the EM wave reflect off
of the plastic or does the plastic have a coating?
=============
It is possibly an aluminium foil reflector sandwiched between 2 layers
of plastic.
I have a 1 metre dia sat dish with the aluminium foil sandwiched between
2 layers of fibre glass/epoxy.

Frank GM0CSZ / KN6WH

Parabolic Dish Questions
 

It grey, won't reflect light very well. Basically I wanted to know how the
beamwidth changed with the larger width dimension vs the smaller height
dimension

Tape aluminum foil to it tobetter reflect light...
John Ferrell W8CCW
Beware of the dopeler effect (pronounced dope-ler).
That's where bad ideas seem good if they come at you
fast enough.

Parabolic Dish Questions
 

"Wimpie" wrote in message
...
On 26 jun, 14:35, "amdx" wrote:
I have a Directv dish 35 inches wide x 20 inches tall 4inches deep.
I calculated the focus as F=D*2 / 16d where D =diameter and d=depth
F=18 inches Ok so far.
How do you find beamwidth? I think the 35" dimensiom would have a tighter
pattern than the 20 ", but how do you calculate,

Second, The feed antenna, There can be different feeds.
A simple monopole, dipole, biquad, patch, yagi, helix.
How does the feed antenna affect the gain of the dish, if at all?
Yea, it my be difficult to light the yagi or helix, so if you like throw
those out.
Thank You,
Mike

Hello Mike,

In case of uniform illumination, gain is maximum, side lobes are
maximum also and beam width is about 60*lambda/diameter (degrees).

My dish is 35" wide x 20"tall
So if Lambda=4.89" Then 60 x 4.89 / 35 = 8.38*
and 60 x 4.89 / 20 = 14.67*
Then my beamwidth will be taller than it is wide.

You will certainly not reach this, for several reasons. The beam width
will be more, it can be twice as high (depending on the illuminator).

Yes. it's always something.

The maximum gain that you can obtain with a certain aperture antenna
is about 4*pi*A/lambda^2. In reality it will be less:

I was going to attempt this but I don't know how to calculate the area (A)
of my non circular dish. Any help there?

Thanks, Mike

Parabolic Dish Questions
 

amdx wrote:
I was going to attempt this but I don't know how to calculate the area (A)
of my non circular dish. Any help there?

Calculus? Graphic solution?
--
73, Cecil http://www.w5dxp.com

Parabolic Dish Questions
 

Area = PI*a*b, as defined below.

http://en.wikipedia.org/wiki/Ellipse

Frank


"Cecil Moore" wrote in message
...
amdx wrote:
I was going to attempt this but I don't know how to calculate the area
(A)
of my non circular dish. Any help there?

Calculus? Graphic solution?
--
73, Cecil http://www.w5dxp.com

Parabolic Dish Questions
 

amdx wrote:
I have a Directv dish 35 inches wide x 20 inches tall 4inches deep.
I calculated the focus as F=D*2 / 16d where D =diameter and d=depth
F=18 inches Ok so far.
How do you find beamwidth? I think the 35" dimensiom would have a tighter
pattern than the 20 ", but how do you calculate,

Second, The feed antenna, There can be different feeds.
A simple monopole, dipole, biquad, patch, yagi, helix.
How does the feed antenna affect the gain of the dish, if at all?
Yea, it my be difficult to light the yagi or helix, so if you like throw
those out.
Thank You,
Mike

Some guys at the local club were trying to use a TV dish like yours.
They eventually decided it was easier to build a dish from scratch.
The old TVRO dishes can be useful and there are plenty of them around
that can be had just for the asking.

Jimmie

Parabolic Dish Questions
 

"Frank" wrote in message
news:0R89k.658$7%6.42@edtnps82...
Area = PI*a*b, as defined below.

http://en.wikipedia.org/wiki/Ellipse

Frank
Thanks Frank,
From the wiki "The area enclosed by an ellipse is ?ab, where (as before) a
and b are the ellipse's semimajor and semiminor axes."
Now back to, why did I want to now that.
Mike

Parabolic Dish Questions
 

Some guys at the local club were trying to use a TV dish like yours.
They eventually decided it was easier to build a dish from scratch.
The old TVRO dishes can be useful and there are plenty of them around
that can be had just for the asking.

Jimmie
I don't know why it would be easier to build one, but yes, I ask and got
three different dishes, so I stopped asking.
Mike

Parabolic Dish Questions
 

"amdx" wrote in message
...


Some guys at the local club were trying to use a TV dish like yours.
They eventually decided it was easier to build a dish from scratch.
The old TVRO dishes can be useful and there are plenty of them around
that can be had just for the asking.

Jimmie
I don't know why it would be easier to build one, but yes, I ask and got
three different dishes, so I stopped asking.
Mike

Hi Mike I missed the post where you said why you wanted the dishes and
what you intend to use them for. What do you intend to use the dishes for?

Jerry KD6JDJ

Parabolic Dish Questions
 

"Jerry" wrote in message
news:2rc9k.26$HY.21@trnddc01...

"amdx" wrote in message
...


Some guys at the local club were trying to use a TV dish like yours.
They eventually decided it was easier to build a dish from scratch.
The old TVRO dishes can be useful and there are plenty of them around
that can be had just for the asking.

Jimmie
I don't know why it would be easier to build one, but yes, I ask and got
three different dishes, so I stopped asking.
Mike

Hi Mike I missed the post where you said why you wanted the dishes and
what you intend to use them for. What do you intend to use the dishes
for?

Jerry KD6JDJ
I didn't say.

Oh, ok. I want to increase the strength of a wifi signal.
Mike

Parabolic Dish Questions
 

"amdx" wrote in
:

....
I didn't say.

Oh, ok. I want to increase the strength of a wifi signal.


Gee, getting relevant information from you is a chore, and you seem to
delight in supplying a partial picture.

Now, what frequency WiFi?

If you are thinking of 2.4GHz, you must already have worked out a feed
solution that efficiently illuminates the small dish, a considerable
challenge.

While you are obsessing about calculating the area of an elipse, you
haven't had a look at the disk from the distant end, have you? It is
probably very close to circular in cross section when viewed from afar in
the direction of the beam.

When you have worked through some of this, you might see why offset feed
dishes made for Ku band aren't widely used by informed people at 2.4GHz.
Of course, there will always be the 'innovaters' with a USB wireless
stick pointing at a garbage tin lid or wok... but that says it all,
doesn't it!

Owen

Parabolic Dish Questions
 

Gee, getting relevant information from you is a chore, and you seem to
delight in supplying a partial picture.

Now, what frequency WiFi?

If you are thinking of 2.4GHz, you must already have worked out a feed
solution that efficiently illuminates the small dish, a considerable
challenge.

While you are obsessing about calculating the area of an elipse, you
haven't had a look at the disk from the distant end, have you? It is
probably very close to circular in cross section when viewed from afar in
the direction of the beam.

When you have worked through some of this, you might see why offset feed
dishes made for Ku band aren't widely used by informed people at 2.4GHz.
Of course, there will always be the 'innovaters' with a USB wireless
stick pointing at a garbage tin lid or wok... but that says it all,
doesn't it!

Owen
Thanks, Owen
Mike

Parabolic Dish Questions
 

amdx wrote:

...
I didn't say.

Oh, ok. I want to increase the strength of a wifi signal.
Mike

You will probably find a lot of help if you "nose" around your local
college (computer/physics/engineering instructors can point you to the
best minds.) The youngsters are all into stretching wifi distances to
the max.

Here is a page to get you started:

http://www.engadget.com/2005/11/15/h...-dish-antenna/

After experimenting with many different antennas at the feed point, I
kept the biquad in the original plans. Your dish is larger than the one
I use (mine is identical to the one on the page--my feed is slightly
modified ...)

Regards,
JS

Parabolic Dish Questions
 

DEAD LINK

http://www.w1ghz.cx/software/hdl_3b4.zip



--
Quote "Get SSL VPN services now, KEEP Government OUT of your
business... "

Parabolic Dish Questions
 

On Fri, 03 Jun 2011 14:50:34 -0500, moronsbegone wrote:
DEAD LINK

http://www.w1ghz.cx/software/hdl_3b4.zip

Ya think? Every link there == "This domain may be for sale"