Advice Needed Unwarping a dish

[RimaNTSS]

Whatever I did the signal dropped so I guess it's okay.

Even if you have LNB not if focus pushing dish in any direction will not necessary give increase of signal, but, most likely decrease.

 

[Captain Jack]

I think you've done well to get it back in shape...
I was going to suggest the exoskeleton method ..but I suspect the Gibby already has this basic structure..

I still want to do this at some point ... Something that would be adjustable. It will do for now though

 

[Nagusia]

Even if you have LNB not if focus pushing dish in any direction will not necessary give increase of signal, but, most likely decrease.

Sorry, you've got me there. I reckon the LNB IS pretty bang on focus - hence anything I do which alters the focus is detrimental. If I found that pushing the LNB arm up (for example) got a better signal then that would indicate the LNB was not in the ideal focal point and be a good reason for trying Huevos' wire idea (or perhaps drilling new holes in the LNB arm where the struts attach). But that's not the case.

 

[RimaNTSS]

I reckon the LNB IS pretty bang on focus - hence anything I do which alters the focus is detrimental.

Yes, if you only change position of LNB and not change position of antenna that is true. Hence, it does not mean you have LNB in focus. Do small experiment: Lift LNB couple of centimeters and than change position of the antenna to get maximal signal. And there you are- another focus! Difference of the signals in those pseudo-focuses, depending on antenna size, could be almost unnoticeable. But, in reality, simple offset antenna has only one true focus.
Finding true focal point for offset antenna is only possible by doing calculations in special programs such as "Parabola calculator" and than carefully measure distances to LNB (place wires). Some people find focal point by placing small mirrors on surface of the antenna and watching reflection.
Perhaps it is also possible to find true focus by lots of experiments (change LNB's position-change antenna's position, measuring signals etc.) Also depends on size of antenna. So, process cold be quiet painful.

 

[Trust]

Very odd what manufactors think about the focus .
The Laminas 1200 came with a new design feedarm for the same dish .
With the laser i found out that the lnb is looking 170 mm higher in the dish as with the old one .

 

[Huevos]

CJ, how do you like having the lnb to the side?

 

[Captain Jack]

CJ, how do you like having the lnb to the side?

Works well, Huevos - I don't have to use the declination jack, except for minor fine tuning. Also, happy that I can have two LNBs - linear and circular. It also doesn't shade any of the dish, unlike on the Channel Master where the large C band LNB sitting above the Ku covered the bottom of the dish from incoming signal.

 

[RimaNTSS]

Unfortunately nothing and nobody is perfect, even CM dishes are not in perfect shape. Today we ( I and @Trust1 ) checked couple of them. Not easy to measure but they have at least 2mm gap between strings. Of course it is possible to fix.

 

[moonbase]

... Of course it is possible to fix.

Hoe do you pull a 1.8m channel master dish back into shape? They have the structural panels on the back to keep them rigid. is there some way to pull them back into shape even though they have these structural panels?

 

[RimaNTSS]

Remember that dish, when it was new, had perfect shape (at least I hope so). And after years of different weather conditions and LNBs pressure downwards, dish slightly changed it's geometry. That means we just wish to give dish it's original shape. If you apply relatively light pressure along red arrows than strings are coming together. Same effect will be if we properly pull edges of the dish backwards. I have seen some dishes with special metal bars- to pull edges back. Some dishes (at least Laminas 2,7m) have special bolts at the back to correct geometry.
By saying all that- yes, it is possible to fix CM geometry.

 

[Archived-1]

Hoe do you pull a 1.8m channel master dish back into shape? They have the structural panels on the back to keep them rigid. is there some way to pull them back into shape even though they have these structural panels?

Hi Dave hanging heavy LNBs from them causes it if there not braced/struts nothing wrong with CM dishes its there owners that don't know how to look after them, have a read here pal .
How to obtain high gain from an offset fed VSAT antenna with a heavy feed / ORU assembly

 

[Archived-1]

And here.
Adjusting VSAT satellite dish distortion

 

[moonbase]

Ah OK, I see now, you pull it back into shape using some type of adjustable bracing and leave the bracing on the dish to keep it in shape. My original thoughts were that if you pulled it back into shape it would then spring back to out of shape. However leaving the bracing in place keeps the good re-aligned shape.

Thx for the info, very useful

 

[Archived-1]

That's it pal, but prevention is better than cure , I will be doing this on my new install.

 

[John]

Ah OK, I see now, you pull it back into shape using some type of adjustable bracing and leave the bracing on the dish to keep it in shape. My original thoughts were that if you pulled it back into shape it would then spring back to out of shape. However leaving the bracing in place keeps the good re-aligned shape.

Thx for the info, very useful

... Good links them Martin, just finished my rear bracing on my 1.8CM apart from some paint, awaiting the 100 x 25mm box ali for the new bottom boom arm to be delivered ready for the lnb rotator and lumps to be added at the front.

 

[Archived-1]

That's a nice little job john, all it takes, plenty of interesting reading from them links J have a look round when you find the time .

 

[Archived-1]

BTW john gale force winds here blowing your way pal

 

[RimaNTSS]

Good job @John What do you think, maybe adding threaded bar along the red line placing turnbuckle (green) to be able to adjust tension? Just a question.

 

[John]

BTW john gale force winds here blowing your way pal

.... She's chained down matey, some strong gusts at the moment

 

[John]

Good job @John What do you think, maybe adding threaded bar along the red line placing turnbuckle (green) to be able to adjust tension? Just a question.

... yes .... good idea that Rims, i'll do that.