Antenna's focal point - "le point G"

[RimaNTSS]

leave it with me a few days pal .

No hurry, take your time

 

[a33]

And now the hardest part starts: There is one sat-specialist on Russian-speaking part of the world, he made program Parabola4, but program on Cyrillic and not all characters appear correctly on PCs that do not have Cyrillic setup.
Program you can download HERE. Later I will explain how to use it, and, of course will inform owner of software if you like it.

I wanted to download this program, but the link is not 'live', alas.
Where can I download it? Would be much obliged....

By the way, can you use this program also for multifeed dishes? That is, dishes as Visiosat (Big) Bisat or Maximum 85 (where the width of the dish doesn't give the right indication for the offset-angle, in combination with hight)?
For instance by giving height of the dish, maximum depth, and location where maximum depth is measured?
I would think a parabola could also be characterised by these three data, or am I wrong?

Greetz,
A33

 

[Trust]

Rob , Zip file in your PM box

 

[Archived-1]

And here to help others .
Finding dish elevation offset angle.

 

[Trust]

And here to help others .
Finding dish elevation offset angle.

There is more needed than the offset angle of a dish to calculate point "G"
Rimants calculated that for mine (and his ) 1.8 m CM , today before the cats and dogs coming down , i put the rotating laser in the lnb holder .
The spot was following exactly the edges of the CM .
And of course every one can ask me for that file .

 

[John]

There is more needed than the offset angle of a dish to calculate point "G"
Rimants calculated that for mine (and his ) 1.8 m CM , today before the cats and dogs coming down , i put the rotating laser in the lnb holder .
The spot was following exactly the edges of the CM .
And of course every one can ask me for that file .

.... Could i be so bold as to ask you for that file then please ;)

 

[Archived-1]

Its only simple algebra and can be worked out from the link I posted, there is an online one here for those who do not know there algebra.
Parabola Vertex Focus Calculator -- EndMemo

 

[a33]

Thank you @Trust1.

But alas, the file you sent me was not the program "Parabola4" that @RimaNTSS used in posts #11 and #13,
but "Parabola2" (which can by the way also be found here: Parabola Calculator version 2.0 This is for @John!)

Parabola2 doesn't calculate the g-spot, though.

So I hope RimaNTSS has the other program still somewhere?


@martin-f: Thanks, I will study that. Though Algebra was not my favorite subject....
Edit: That site is only for Prime Focus dishes, though; not for offset parabolic calculations, if I understand correctly?

Greetz,
A33

 

[RimaNTSS]

That is newer version of the program Parabola6 hope you can download it now.

 

[Trust]

@ a33 and @ John , sorry guys i did send you the older version .
I also do have Parabola6

 

[a33]

That is newer version of the program Parabola6 hope you can download it now.

Thank you!
I am curious if it has new possibilities to/over version 4 (in relation to my question a few posts earlier); but that has to wait till tomorrow....

Greetz,
A33

 

[Captain Jack]

.... Could i be so bold as to ask you for that file then please ;)

And me

 

[a33]

Beautiful program!

My question from above is still unanswered, though:
Is there a way tot calculate the offset angle and focal distance of a multifeed dish?

In the horizontal plane such a dish is not a parabola, I understand, but more or less spherical; but in vertical plane it should be a normal part of a parabola.
By measuring the depths of the dish in the vertical plane, can you calculate the assumed width for as if it was a normal parabolic dish?

Greetz,
A33

 

[RimaNTSS]

Unfortunately, for this program you have to know big and small axis and depth. If you do not know horizontal size than finding out offset angle and focal distance is more difficult but still possible task. Some ideas how to do that:
- show picture of your dish and ask users of the same dish, may be they know some data;
- look in manufacturer's manual, perhaps they have mentioned offset angle;
- calculate (somebody has mentioned simple algebra before );
- if simple algebra does not work, look for another program;
- other solution.

Once I had an idea how to find out horizontal axis on multi-focus antenna by using dust tape and some water But did not do it in practice.

 

[a33]

Thanks.

I will try to calculate the offset angle with the measurement of hight of the dish, and top string and bottom string to the focal point (LNB feedhorn) of the dish. If the present LNB-spot is not as accurate as I would like, that calculation wouldn't be accurate either, alas.

I'll try searching on the web for a program that calculates focal point and offset angle purely out of (multiple) measurements of the depth of the dish. If someone knows such a programm, please tell me...

Greetz,
A33

 

[RimaNTSS]

program that calculates focal point and offset angle purely out of (multiple) measurements of the depth of the dish. If someone knows such a programm, please tell me...

There is ONE for you, perhaps it is only one, at least I did not see others. It can take some time till you find out how it works, but then it really works.
And you do not want to hear about dust tape and water method for finding width of the dish?!
And, please show some pictures of dish you have in mind.

 

[a33]

There is ONE for you, perhaps it is only one, at least I did not see others. It can take some time till you find out how it works, but then it really works.
And you do not want to hear about dust tape and water method for finding width of the dish?!
And, please show some pictures of dish you have in mind.

Thanks again. I'll look into that program next week.

The multifeed dish I have in mind is a Visiosat Bisat I have lying aroud. I 'stole' some pictures of the internet: see attached.

I understand the horizontal plane of such a multifeed dish is more sferical than parabolical, to create multiple focal points (a focal line).
Isn't the water-method for purely parabolical dishes (both vertical and horizontal)?
I don't know the dust tape method; how does that go?

I would like to make this dish suitable for someone, not only to watch 13-19-23-28e, but also 9e and 5w, all on this one dish. I've seen on the internet that 5W is really do-able in this configuration. (Alas, 26e not possible between 23 and 28e.)
I would like to check the position of the central LNB (am curious how that can best be done with a multifeed dish, reading all the posts about ill-placed LNBs), and skew the whole dish (that must be DIY, no skewable bracket there). I guess skewing the whole dish would be best specially for 5W, to have as much sight of the dish as possible.
Then calculate the correct LNB-distances to see if improvements are possible (in the present holder the LNB's look in all directions (due to lack of space, I think, because the holders are rather thick).

Would be nice project for next spring or so.

greetz,
A33

 

[RimaNTSS]

For your dish you will not need dust tape, as dust tape is needed to close holes in the surface of the dish to prevent water running out
Agree with you about skewing of whole dish, that gives better results that lifting/lowering LNBs in multifeed.

 

[a33]

There is ONE for you, perhaps it is only one, at least I did not see others. It can take some time till you find out how it works, but then it really works.

Indeed, it took some time
But there is google and google translate, that helps!
See Советы бывалого "чайника" :: Просмотр темы - настройка оффсетной антенны - по умному Strive - DishChar
and the links in that thread. (There is also another link to download the program.)

In the DishChar program you should give estimated focal distance of original PF-dish (e.g. distance from bottom dish to LNB-holder), estimated offset angle, and measured hight of the dish.
You then can check the given parabola with measured points of your own dish.

The measurements of the dish surface make a triangle each time: from bottom of dish, to (measured) point on the dish, to top of the dish. So it's like this:
-straight line of 100 mm from bottom of dish to a point further up the dish (exactly 100 mm further!)
-measurement of straight line from that last point to top of dish
-line from top of dish to bottom of dish (this is of course unvariable: the HEIGHT of the dish, and filled in earlier)
And then the same for distance 200mm, 300mm, 400mm, etc.

NB: this way the x-hundred mm plus the measured extra lenght should always be bigger than the hight! The highest value should be somewhere near the deepest point of the dish.
The measured points are given with red dots, with which you can check if you have a fit, or should change focal distance or offset angle in your estimation.

The strange cyrillic/russion characters in the menu options are mostly options for the view, not for dish-characteristics. So one doesn't have to bother about those...

Neat little program! Thank you Rimantss! (By the way, do you understand russian or all that is given in these programs, yourself?)

BTW2: What is dust tape? I searched with google, they only know duct tape....? Or is it a pun?

Greetz,
A33

 

[RimaNTSS]

@a33 Dust tape any tape which can stick to surface, not pun

do you understand russian

Do I understand Russian.... well... I was born halve century ago in Latvia (soviet times, you know) then everybody was obliged to speak and even study in Russian. So, yes, I can understand that language, can tell anecdotes, and can even thing in it.