Make Gregorian dish

RimaNTSS

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Hi All! Last time I see more and more people mentioning that Gregorian type dish performs better than usual offset. So why do not we discuss here how to upgrade your existing offset dish to make it perform hopefully better up to 10%. So, idea is to design and make sub-reflector (SU:cool: which will fit your antenna.
And all you need for calculations of SUB is illumination and offset angles of your antenna. What do you think about this idea?
If we see that making of SUB is not plausible way forward, we can discuss how to use original Fibo SUB and attach it properly to another antenna (usually bigger) and still get improvement of performance.
 

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If anyone can, then it's you Rima :D just show us how it's done1
 

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I mostly was thinking about discuss, calculate, argue etc. Create SUB would be final step and would depend on users technical possibilities (I do not have such at the moment).
Dual reflector shaping ?
Yes, Dual reflector, Gregorian type. From that Dual, everibody already have half- which is main mirror. Only missing part is SUB.
 

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I will leave you with it :D I only started reading up on it a few days ago due to the same thread :)
 

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I propose do not go very deep in theoretical arguments and use simple drawings without lots of mathematical formulas and difficult calculations. But, we will need to recall from school times some geometrical terms and explore more closely what tha heck is figure called Ellipse.
And I hope we are not in big hurry and can proceed slowly.
 

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Ellipse http://mathworld.wolfram.com/Ellipse.html
In that geometrical figure pay attention to two dots inside Ellipse- Foci (F1 and F2). In our Gregory antenna system those two dots will be crucially important. All radiation from satellite, reflected from main mirror will go through F1, reflects from SUB (shaped as part of rotatory ellipsoid) and comes together in F2 where LNB is located. Forgot to tell, we better calculate our SUB to be used together with Inverto Black Ultra (IBU). This is most affordable and good LNB on today's market.
 

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Rima do you want to suggest a dish make for our theoretical prototype and apply all design/calcs/manufacturing ideas to that one make? I think it might be easier to try to figure every thing out for one make first, then if it is successful expand those methods to different makes. What do you think?
 

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What do you think?
Good idea, Riverblue! Lets do it on your dish. What do you have available. I have no preference. It should be offset, preferably ~1 meter or more.
 

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Chanel Master, of course :D, I have got a spare 1.0m kicking around!
 

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Great! Do you know illumination angle of your dish? This, basically only dish parameter we will use. At the later stage we will also need to know offset angle of dish. Size of dish not really matters. So, two angles, do you know them?
 

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Long time no answer! I see that you do not know your dish! And there is nothing wrong with that not knowing. Illumination angle of dish could be taken from technical data or calculated. But, we are not in hurry and have time to better understand our antennas :D And we need to know only one angle (I marked it ?* in green color). Do not worry, take your time :rolleyes:
 

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Riverblue

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Offset angle is 22.6⁰, having trouble finding out the illumination angle.
 

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Offset angle is 22.6⁰
Offset angle we will need at the later time. Now only illumination angle: angle from Focus and between lower and upper part of working area of your dish.:-buttkick
 

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Perhaps here you can find information about calculation of Focal point of offset antenna and, consequently it's illumination angle.
 

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Can't find any info re Channel Master Dishes on the internet and their illumination angle, I've been searching hard, that's why it's taken some time to respond. Thanks, but I did follow your thread re focal point and I was aware of the site to make calcs from :). I will have to take some measurements off of my dish in daylight tomorrow to ascertain a correct angle.
 

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I maybe mixing terms... That angle should be called opening angle not illumination one? You know, sometimes I am mixing shirt/skirt, gays/guys etc.
Taking measurements of your antenna be prepared that A-B and C-D could be measured easily, but depth of antenna is not easy measurable with needed precision. :cool:
 

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Ok, been outside, measured my 1.2m CM, too much hassle to get my roof ladder out to measure my 1.0m CM :)

According to my measurements the opening angle of the 1.2m is 78.2⁰, but that is with the focal distance unchecked (see below)

I tried your Parabola4 download, but I'm a mac user so no good because it's windows.
Here are my measurements if someone else wouldn't mind running them through Parabola4 for me, thanks; A-B= 1300mm, C-D= 1200mm, E-H= 116mm
Instead of stringing I used a machined aluminium straight edge across the face of the dish, it is absolutely straight, it's too windy for string today, it resonates in the wind.
 

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Seems that you measured your dish quiet precisely. Program shows offset angle 22,6* (as you mentioned earlier), and opening angle precisely 80*. I circled those numbers red. ScreenHunter_52 Oct. 19 16.45.jpg ScreenHunter_51 Oct. 19 16.45.jpg Circled green distances from Focus to UP and DOWN points of antenna. And blue is distance from Focus till you know what.... "Le point G" :-rofl2
But, now we will only use opening angle of your antenna, which is 80*.
So, lets draw two crossing lines with 80* between them. Something like this ScreenHunter_53 Oct. 19 16.59.jpg
 

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And now, lets speak about IBU. Can anybody provide it's opening angle and also place on it's body dot which will represent focal point?
 
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