Anyone tried to make BIG dish at home?

I would hazard a guess that the signals are not being co-phased at the correct point. I'm not familiar with Fresnel antennas, so can't really comment, but my first concern would be whether f/D calculations for a parabola can be applied to a Fresnel.
 
casser said:
That was my first idea, conical horn have lower noise than the Dish...but i´ve build different kind of antennas (not all was conical) and the difference of 3dB was always accomplished using antennas that doesnt use reflector, maybe using reflector´s give higher noise to the antenna, i dont know...my RF knowledge is very low, this is only a hobby:)

So i have no gain/loss with the polarization in Conical Horn?
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In land based microwave dishes, sometimes a "precision" dish is used. This is a ring of metal around the outer circumference of the dish. It is anywhere from 80 mm to 500 mm in depth. It is used to reduce unwanted signals from other transmitters on nearby paths. In satellite Clarke Belt assignments nearby satellites can degrade signals on a parabolic dish. Signal Quality is reduced and therefore the received signal is not as good as it could be.

One could assume that a cone feedhorn aimed at a satellite will have less signal quality degradation from adjacent satellites. This could be due to the "precision" selectivety of the cone.
 
casser wrote-

(-The difference between the Conical and Dish performance is that the Conical need´s 50% less diameter to get the same result´s of a Dish..what does it mean 50% of diameter? for each 6dB you double the diameter..so 50%=3dB. What usually mess up with 3dB? The polarization.)


Are you saying that a one meter dia. cone performes like a 2 meter dish?

If so how long would it be? :eek:
 
FYI-

http://www-sop.inria.fr/prisme/fich... times but could not upload picture:confused:
 
1 meter Conical Horn will perform +-1.5meter Dish...i didint do the calculations, but it should have more than 4meter lenght for sure.

A 25dBi (20cm) conical horn can receive without freezes a 54dBW satellite...this explains how good Conical Horn can perform. My "personnal record" is receiving the same 54dBW satellite with a 10cm diameter version with a bunch of freezes, but i was getting image and sound:)

If you squeeze the conical horn in some sections, you will get a boost of 1/2dB in some frequencies, but loosing in another frequencies. Also you can squeeze the conical Horn to turn from a "circular shape" to a "ellipse shape" and getting the same result´s.

But is not practical a "big dish" conical version...we need a different kind of antenna:-Nooo
 
casser said:
But is not practical a "big dish" conical version...we need a different kind of antenna:-Nooo
Click to expand...

A SelfSat kind of a flat "dish"- that looks more like a squarial is a RECTANGLE 50cm x 30cm and it equals in performance a 60cm offset dish. So a flat rectangle antenna 5m long is only 3m high and equals a 6m dish. But the big question is; Is it easier to make than a prime focus dish for Ku-band?
 
casser said:
1 meter Conical Horn will perform +-1.5meter Dish...i didint do the calculations, but it should have more than 4meter lenght for sure.

A 25dBi (20cm) conical horn can receive without freezes a 54dBW satellite...this explains how good Conical Horn can perform. My "personnal record" is receiving the same 54dBW satellite with a 10cm diameter version with a bunch of freezes, but i was getting image and sound:)

If you squeeze the conical horn in some sections, you will get a boost of 1/2dB in some frequencies, but loosing in another frequencies. Also you can squeeze the conical Horn to turn from a "circular shape" to a "ellipse shape" and getting the same result´s.

But is not practical a "big dish" conical version...we need a different kind of antenna:-Nooo
Click to expand...

casser-

Last night my organic memory bank ( Brain ) retreived some interesting data.

I saw a picture of a folded cone antenna that was used in very early days of satellite communications. As I recall, it was made by Bell Laboratories or AT&T and was in the New England states here. It may have been one of the first Trans-Atlantic systems between America and Europe. The cone was cut into a 90 degree shape. The antenna was motorized. Assume prior to Geostationery Satellites. In that it was mostly horizontal, with only the aperature pointed skyward, it was more practicle.

I guess that this was before semi-conductors could reach the Ghz range. They did have parabolic dish antennas for UHF point to point use. So the dish technology could have been used. It seems that a folded cone antenna would be much more compact. It would be interesting to see results for a folded cone antenna. Your the expert, what do you think?

I mentioned earlier the AT&T land based microwave system that was used early on, it used rectangular folded feedhorns. Again, in the era of microwave technology "Klystron". "Valve" = "Thermeonic Transducer" = "Vacuum Tube".

From this it would seem that what you say about direct feedhorn antennas is valid. When high gain LNA's surpassed "valve" technology the engineers put them on a dish. Much smaller in size with some gain to waste for the new high gain LNA. Also the associatd waveguide loss was "overcome" and of course a dish is easy to motorize. "LNA" = Low Noise Amplifier" = Prior to LNBF = "low noise amplifier block down convertor".
 
divibi said:
A SelfSat kind of a flat "dish"- that looks more like a squarial is a RECTANGLE 50cm x 30cm and it equals in performance a 60cm offset dish. So a flat rectangle antenna 5m long is only 3m high and equals a 6m dish. But the big question is; Is it easier to make than a prime focus dish for Ku-band?
Click to expand...

I'd be a bit sceptical about that performance claim. I did a bit of development on satellite panel antennas 15 years ago - and from what I can recall the performance (at the time) was not comparable with a dish. I would expect that inside the box is a phased array of square panels, the size of each panel is determined by the frequency (a mode of resonance occurs dependant on the circumference). I would also expect two feed points, one for horizontal and one for vertical, the matching of each panel is achieved by the size and effective dialectic from the feed point to the panel (I assume it's not directly connected). To improve performance (lower beam width and higher gain) I would expect at least one director in front of each panel, these aren't parasitics as such, but do focus the beam (in a YAGI sense some people might refer to them as parasitics). If these panel antennas don't have directors then I would suggest you might be able to squeeze a bit more out of them by adding them, the easiest way to do this would be to etch directors onto a PCB, mind you, without a network analyser it may be a bit difficult to get right ad-hoc.
 
divibi said:
A SelfSat kind of a flat "dish"- that looks more like a squarial is a RECTANGLE 50cm x 30cm and it equals in performance a 60cm offset dish. So a flat rectangle antenna 5m long is only 3m high and equals a 6m dish. But the big question is; Is it easier to make than a prime focus dish for Ku-band?
Click to expand...


During the last OJ Simpson trial, I noticed a new Satellite Antenna being used. It was "Rectangular" in shape but was formed with Parabolic characteristics. "Who said a Parabola had to be round"?
Maybe a rectangular LNBF?

Does a rectangular feedhorn yield more seperation between signals than a round "NotCircular"? What does the satellite use? Round or rectangular? Pro stuff could take advantage of this.

Do you have any additional information on this design?

Where did you get your comparison data?

I have noticed that some hotels here are using a horizontal section of a parabola type of antenna, but I assume it is for one specific linear polarity. "Horizontal" I would guess.

Please explain what a "SelfSat" is. :)

Now I know what a "SelfSat" is, reminds me of when I tested cellular mobile antennas, there was a lot of bogus stuff in the market.

Military Planar antennas are used because of their ability to be "Steered Electronically". Moving dishes for incoming war heads proved to be too slow. Metawave used a planar antenna for cellular with a steered beam ( feeding rf at different phase relationships to dipole arrays. This was said to allow the cell site to track a particular mobile for enhanced coverage without interfering with other cells.
 
Satcom1 said:
Please explain what a "SelfSat" is. :)
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Help yourself have a read _http://www.self-sat.com/sub02_2.php
 
Selfsat is to complicated to build one (see attachement)..it´s to complex, that should be one of the reasons for being so expensive! There were 2 good pictures of the antenna inside in portuguese forum´s, but imageshack for some reason deleted the links:mad:

About the performance (according to portuguese users using it), the smallest selfsat version will have the performance of a 60/70cm offset dish, i believe that´s possible, since a 33dBi Conical Horn should equal to a +-70cm dish..

I dont think that it´s going to be a 2meter Selfsat version...the biggest version they have it´s only 34.5dBi, most probably due complications in getting bigger designs with the same efficiency/performance (again with my theories:)).

I tried many modifications on Conical horns to reduce the lenght..but none work, but i´m still hopped in my fresnel-conical-based project, i think that my 30cm version it´s performing between a Conical Horn and a dish..but the 60cm version not worked very well..
 

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*makes notes in head*
This is very interesting.Thanks everyone!

Karis
 
Satcom1 said:
Now I know what a "SelfSat" is, reminds me of when I tested cellular mobile antennas, there was a lot of bogus stuff in the market.

Military Planar antennas are used because of their ability to be "Steered Electronically". Moving dishes for incoming war heads proved to be too slow. Metawave used a planar antenna for cellular with a steered beam ( feeding rf at different phase relationships to dipole arrays. This was said to allow the cell site to track a particular mobile for enhanced coverage without interfering with other cells.
Click to expand...

To be fair, a lot of the development that I did was with cellular panel antennas - the satellite project wasn't 'mine', but used the same principles, so information was shared. I was going to suggest that it would be interesting to introduce phase delay to slew the beam, effectively you could 'steer' the beam from bore sight, done with the right phase delay you could also steer to inclined orbits.
 
As supplier said, that dish can be used for both C/Ku bands and gain at 12.5ghz is declared to be 47db.
 
If the 47 dB(?) claim refers to a 128 panel antenna (as in post 171) and you assume that you would have to double the array size to increase the gain by 3dB then it would follow that:
47 dB = 128 panels
44 dB = 64 panels
41 dB = 32 panels
..........27 dB = 1 panel !

Even with the lower claim of 34.5 dBi it would equate to a 13.5 dBi gain for a single panel.
 
With reference to (my) post 168 - it's not just the effective dielectric that matches each panel, it's the position on the panel of the feed point (with relation to the centre / edge of the panel). The positioning of the feed point will be apparent on the resistive plane (as seen on a smith chart), and the dielectric will be apparent on the capacitive (/inductive) plane.
 
I discovered that the cones in my Fresnel Antenna should have been "STACKED" TOWARDS THE lnbf. Also this was not a true FRESNEL LENS antenna, it is a "CONICAL STACKED ANTENNA" A WHOLE NOTHER ANIMAL.


_http://solarcooking.wikia.com/wiki/Fresnel_reflectors

Since I am not able to upload .jpg files anymore I've inserted this link to a websiate that shows more details of a Conical stacked array and a true Fresnel Lens collector.

I find these interesting, but it is likely that they will not work properly with a DVB signal. Possibly due to the concentrated signal not being completely in phase.

Since this, I have made a fiberglass parabolic dish by inflating a six foot diameter balloon and covering a 1.8 meter dia. with fiberglass. :-rofl2

It seems to be a perfect parabola and you can even make an offset dish by applying the glass over a 22 degree slant of the balloon. Weather balloon, the kind some folks here attach to their lawn chairs and go flying. :-worship

The interior surface is as smooth as a babies butt and takes the zinc paint to form a conductive and reflective surface. :cool:
 
I discovered that the cones in my Fresnel Antenna should have been "STACKED" TOWARDS THE lnbf. Also this was not a true FRESNEL LENS antenna, it is a "CONICAL STACKED ANTENNA" A WHOLE NOTHER ANIMAL.


_http://solarcooking.wikia.com/wiki/Fresnel_reflectors

Since I am not able to upload .jpg files anymore I've inserted this link to a websiate that shows more details of a Conical stacked array and a true Fresnel Lens collector.

I find these interesting, but it is likely that they will not work properly with a DVB signal. Possibly due to the concentrated signal not being completely in phase.

Since this, I have made a fiberglass parabolic dish by inflating a six foot diameter balloon and covering a 1.8 meter dia. with fiberglass. :-rofl2

It seems to be a perfect parabola and you can even make an offset dish by applying the glass over a 22 degree slant of the balloon. Weather balloon, the kind some folks here attach to their lawn chairs and go flying. :-worship

The interior surface is as smooth as a babies butt and takes the zinc paint to form a conductive and reflective surface. :cool:

I have found a URL that includes a Excel Spreadsheet for making a segmented Parabola from a flat sheet. I will build one to replace the "Conical Stacked Antenna".

This type of antenna has flat petals but can be made more effective by spinning it with an epoxy slurry inside. This is how some Astronomer Hobbiests make their lenses. It should be perfectly accurate and not require a lot of Epoxy because 90 percent of the parabola is already there.

I will make a folded cone antenna by cutting a 45 degree cut through it and rotating it to a 90 degree offset. This should make a cone that is much more managable t
 
Satcom1 said:
Since I am not able to upload .jpg files anymore I've inserted this link to a websiate that shows more details of a Conical stacked array and a true Fresnel Lens collector.
Click to expand...


Nobody is stopping you uploading your jpg files to our server that is exactly what we want..... what we do not want is links to jpg files on other servers. If you are unable to upload files to here PM me, but basically when posting again scroll down to the manage attachments button and click on it
 
Topper said:
Nobody is stopping you uploading your jpg files to our server that is exactly what we want..... what we do not want is links to jpg files on other servers. If you are unable to upload files to here PM me, but basically when posting again scroll down to the manage attachments button and click on it
Click to expand...


Topper-

Sorry, I tried what you suggested while I tried to post .jpg files several times and it did not work.

The files appear to upload when viewing the "progress bar" but when I have gone back to the manage attachments section they do not appear.

This is a great site, and in the future i will try again to upload .jpg files. i have noticed that in the past other members have had this same problem but it seems to clear on it's own.

I'll be mre patient. :cool:
 
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