Advice Needed mabo 1.85m offset dish whats its parameters?.

[butchyboy]

any one have details on this dish?,all i know i think it was polish made.
the offset angle postion of the focal point and the lnb,s aiming point on the surface of the dish?.

i always taught you aimed the lnb to the dish centre,but rimnants says no not at all.
so where would be the best part on the dish surface to aim the lnb weather its ku lnb or cu lnb.

 

[mikeisyou]

How to find the focal point of a satellite dish:

Basically wait for a sunny day with no clouds in the sky, get a piece of paper and see where the spot is.

 

[butchyboy]

How to find the focal point of a satellite dish:

Basically wait for a sunny day with no clouds in the sky, get a piece of paper and see where the spot is.

how are the getting the sun to relect on to the paper?,as the dish face would not reflect the sun like that on to the paper at lnb face.
i notice the have a few small round circles placed of sides of dish face and at top middle and bottom.
are the using small bits of glass and thats how the are feflecting back on the paper ??.

 

[mikeisyou]

Are those metal reflectors? Could be

 

[butchyboy]

View attachment 135889

Are those metal reflectors? Could be

how do you know where to correctly place them metal reflectors on the dish??.

 

[Analoguesat]

how do you know where to correctly place them metal reflectors on the dish??.

You can see the refelctive studs clearly from about 5:10 on the video. You just stick them on - they will reflect according to the curvature of the dish

 

[butchyboy]

Yup - you can see them clearly from about 5:10 on the video

yes but where would you correctly place those pieces on the dish,i see 4 bits of a cd would do the job.

 

[Analoguesat]

You read my reply too fast - I edited it but you read the first version

Just stick the reflectors on - it will be close enough

 

[Analoguesat]

Id guess the original support arms either got damaged or lost which is why they were trying to cobble together new ones. Any original dish should be pretty much spot on with the focal point

 

[butchyboy]

Id guess the original support arms either got damaged or lost which is why they were trying to cobble together new ones. Any original dish should be pretty much spot on with the focal point

thats exactly what i was thinking as regards the manufacters arms that come with the dish should be pretty much bang on.

 

[Gladstones]

how are the getting the sun to relect on to the paper?,as the dish face would not reflect the sun like that on to the paper at lnb face.
i notice the have a few small round circles placed of sides of dish face and at top middle and bottom.
are the using small bits of glass and thats how the are feflecting back on the paper ??.

he said get pieces of mirror and stick them on the dish one in the middle and 4 on sides bit before the outside edge

 

[a33]

any one have details on this dish?,all i know i think it was polish made.
the offset angle postion of the focal point and the lnb,s aiming point on the surface of the dish?.

i always taught you aimed the lnb to the dish centre,but rimnants says no not at all.
so where would be the best part on the dish surface to aim the lnb weather its ku lnb or cu lnb.

I guess most is here: Antenna's focal point - "le point G"

Easiest way to 'find' position of focal point and G-spot is by calculating, I find.
Needed are measurements of width and height of (working area of) the dish, and exact depth at a certain dish height (the center of the dish is easiest).
Then put them in a calculator; Parabola_6 by strannik is excellent, and mine is also good (but not available on the internet; though I can make a screen picture with the results).
(Parabola6 needs depth at the center. For other height locations other equations are needed.)

Greetz,
A33

 

[a33]

BTW One thing I forgot to mention:
This calculation with just three needed inputs assumes a dish with a flat dish face.
So with the string test: the strings across the dish face are all barely/just-about touching.

For a paraboloid wider than high dish, see e.g. Measuring and calculating zone-1 and zone-2 dish
(ignore the not-so-funny reaction by channel hopper there.)
And also see here, for background: Just Sharing This - Calculation of the focal length of an offset satellite dish antenna, Revisited
You need four input measures, for these wider than high dishes.

For a multifeed dish (only parabolic in the vertical sense) I have derived some equations to calculate offset angle and focal length from multiple depth measures, at various 'heights' of the dish. I haven't automated that calculation in a spreadsheet, yet.
In theory, two depth measurements of the dish would be enough. However in practise, these depth measurements easily have inaccuracies, so you need in fact multiple measurements to level out these inaccuracies as best you can.

Greetz,
A33

 

[butchyboy]

Fishing line horizontal and vertical on the dish and it's touching.
Depth of dish surface to fishing line is 19cm

 

[a33]

Depth of dish surface to fishing line is 19cm

So subtract height of dish rim, to get the depth of the paraboloid surface? And it should be to mm precise, or rather (if possible): to 1/2 mm, or 1/4 mm.

And height and width are needed, also without dish rim.

greetz,
A33

 

[butchyboy]

Height and width

 

[Captain Jack]

You need to measure it so the tape is straight over the surface from rim to rim. Else it'll measure it longer/wider than it actually is.

 

[butchyboy]

You need to measure it so the tape is straight over the surface from rim to rim. Else it'll measure it longer/wider than it actually is.

oh i taught you had to make sure tape measure was on the whole front dish surface.
thanks captain.