Antenna's focal point - "le point G"

[RimaNTSS]

I do not think Parabola4 or any other known programs can calculate properly not-standard dishes like you have or others (toroidal, square-shaped, multifocus). In case of non-standard dishes it is only one way ahead- trust in manufacturer's designed feedarms and LNB holder.
This scrap dish you have: did you measure working area of it or full size?
Maybe it should stay in scrap?

Add: Can you post better picture of your dish?

 

[RimaNTSS]

Meant the two pins H & V in the circular space.

Those two pins should be positioned only by skewing LNB (turning it in the holder).

 

[battenfan]

Working area. It's beveled around the edge witch makes measurements a little harder. I'll see what a can do about the pic, I only have the one phone.

Thanks for a great thread btw.

 

[RimaNTSS]

Forgot to report about progress happened couple of weeks ago: My trustworthy friend Trust made adapter for my boresighter. He also inserted 3 screws (made of INOX! ) to be able to calibrate the laser beam. And finally he made switch for laser ( it completely amazed me, and also INOX!), so now I will not need to insert batteries when I wish to turn laser on and remove them to stop it.

 

[skomedal]

Keep us informed.

Don`t forget the 90 degree markings to check beam if centralized when rotated on axis for testing.

Regards

 

[RimaNTSS]

I would like to dig out this old and not very popular thread just for reason that I think there is no user's common view on where is antenna's working area. Some (including producers and second-hand sellers) measure dimensions of their dishes from edge to edge and show those numbers, and that is because they wish to sell small product for bigger price pretending their dish is bigger. In reality, working or active area is usually smaller (like TV set, you usually measure screen diagonal, and even more- diagonal of part of screen which shows some picture).
Basically, working area of dish stops there where surface geometry (parabola) changes it's shape in such a way that microwaves reflected will not be going towards LNB. I am attaching couple of pictures with RED-dot marking point where working area of the dish starts/ends. So, to measure our dishes properly we should make such a red dots on antenna's surface to mark points A,B, C and D. And afterwards- measure vertical axis (A- and horizontal axis (C-D)

 

[Archived-1]

I see what your saying Rimants, I will re measure the dish tomorrow and get back to you pal.

 

[RimaNTSS]

OK, Martin! As I see you are pretty ready to do some measurements on your CM1,8m before it is installed. Great!
This picture can help you. I have already put some data there, but it is just an example, will be changed to the proper data after you get it
Remember that you should find proper places for dots A, B, C and D. Keep in mind that distances A-C, C-B, B-D and D-A should be equal. A-B and C-D distances should be measured with the precision up to 1mm.
Depth measurement should should be done with the precision up to 0,1mm from point where lines A-B and C-D cross each other.
And, could you also do one additional measurement- distances between holes, throughout which bolts xix dish to the mount?
Thanks in advance.

 

[Archived-1]

^^^ will do Rimants

And, could you also do one additional measurement- distances between holes, throughout which bolts xix dish to the mount?

Do you want centres measurements ?

 

[RimaNTSS]

Martin! Does not really matter. I just "made" 2 white additional holes in the dish. Distance between centers of the holes will be exactly same as distance between edges of the same holes. I wold suggest to make measurements between edges of the holes- will eliminate possible mistake.

 

[Archived-1]

because they wish to sell small product for bigger price pretending their dish is bigger.

Certainly not with the CM 1.8 its 1957 x 1812 mm not working area though

 

[Archived-1]

Hi Rimants, I get top to bottom 1945 side to side 1800, depth to centre of the dish using a straight edge 177, dish holes centred 607.

 

[RimaNTSS]

Thanks Martin!
To add more precision....could depth also be 169,7mm?
And can height of the dish be little bit more than 1945mm?

 

[Archived-1]

Thanks Martin!
Are you sure it is 117 and not 170 or 177mm?

Yes sorry Rimants, 177, I will edit my post to save confusion.

 

[RimaNTSS]

Martin! When you have possibility, could you re-check antenna's dimensions. According to antenna's passport its offset angle is 22,62* and if we put your data 1800x1945mm to the calculator, it gives us 22,3*. So, something is wrong here. If were vertical size be 1950mm than offset angle will also be perfectly matched.

 

[Archived-1]

1950 it is then, it was hard to hold the tape measure and see the other end so I deducted 12mm presuming width and height had the same deduction for working area

 

[RimaNTSS]

It is better to put across antenna some wooden plank or aluminum angle, and then make pencil-marks exactly where working area starts.

 

[Archived-1]

It was late last night when I checked the measurements and didn't have time/light to mess about too much, your calculator has put thing right at the end of the day

 

[RimaNTSS]

Martin! There is no hurry at all. We can continue over and over again. But in some cases, it is better to know some things certainly, such as CM1,8m parameters. So, when you have time and mood for final measurements, please do that with the maximum precision you can. That can help many users in the future. You could also measure deepest point of the parabola and distance to this point from bottom or upper point. Thanks in advance.

 

[Archived-1]

Ok Rimants, when I start to install the floor in the SH, I will have to roll the dish out onto the lawn to do the work, and I will check precisely, once I have the roof installed I can relax a little and find time to play, leave it with me a few days pal .