Advice Needed Unwarping a dish

Captain Jack

Captain Jack

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Chaps, my newly acquired Gibertini 1.5m dish is warped. There's about 1-1.5cm gap between the strings... Is it possible to successfully unwarp it? Do I just place it on a flat surface and put some weight on top (where)?

To ensure I strung it correctly, I did the same thing with my Channel Master and there was no gap.
 

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I had about 15mm gap between horizontal and vertical strings on my T90. That is what I did: placed threaded bar (18mm in diameter) behind the dish, made 2 holes in edges of the main mirror, and then applied static force to those edges till gap between H/V strings disappeared.
 

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Captain Jack said:
Chaps, my newly acquired Gibertini 1.5m dish is warped. There's about 1-1.5cm gap between the strings... Is it possible to successfully unwarp it? Do I just place it on a flat surface and put some weight on top (where)?

To ensure I strung it correctly, I did the same thing with my Channel Master and there was no gap.
Click to expand...
What made you string it. Was there something wrong with the performance?
 
Yes, performance of about 1m dish. Didn't even get near the signal quality levels of my 1.2m Channel Master.

The dish isn't creased ... just seems warped. Will see what I can do tomorrow, else the 1.2m CM is going back up. Stupid flappy aluminium....
 
Captain Jack said:
Chaps, my newly acquired Gibertini 1.5m dish is warped. There's about 1-1.5cm gap between the strings... Is it possible to successfully unwarp it? Do I just place it on a flat surface and put some weight on top (where)?

To ensure I strung it correctly, I did the same thing with my Channel Master and there was no gap.
Click to expand...
Is that not what VS has just done with the plates he has made ? Personally if your going to go for something as big as 1.5 i would do what I have done and go that little further and got 1.8 CM you wont have that problem with them.
 
The 1.5m was always going to be an interim measure as I do want the 1.8m at some point. And it was a no-brainer for £80... It's just a bit pointless where it is now (even the 1.2m is pointless) due to poor line of sight to eastern sats. I even thought about chucking the 1.2m away and using my 1m dish above the gutter on the side of the house. Would have a full view of the entire arc from there - especially with the wonderful 1224 motor.

Got some more advice on unwrapping the thing, so will give it a go tomorrow.
 
Take a (good) picture from the near side of the dish, looking at the point where the far rim just comes into view. Both should be in the form of stright lines and follow each other exactly.

If you are able, do the same from top to bottom, and then the diagonals.
 
Once you unbolt it from the backplate the 1.5m dish face is a big wobbly sheet of aluminium. With mine I used the meter to get it in focus the best I could. Just went round the rim bending it forward or back to get the maximum signal. Still wasn't right so I added a bit of stainless wire from the top of the dish down to the LNB arm. That made loads of difference.

C-band-LNBs-1.webp
 
timo_w2s said:
What's your top Black Ultra for?
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Not there anymore. Any satellite that is inclined 3-4º and in the south of its travel. I could get Astra 1C/D @ 2east for about 8 hours a day with this setup.
 
What a coincidence, I also bracketed an extra LNB above the Black Ultra two days ago!
Just out of curiousity. AMC-14 at 29.5º E comes undisturbed by 28 East of course, locked a few transponders.
Took it away meanwhile, my curiousity was satified and it would be a burten when adjusting the skew of the main LNB!
 
A few years ago the 120 Fibo of my friend PaulvR was blowen backwarts with the stand , extremly warped , even receiving astra 19.2 was impossible .
We put it flat on the floor and at the 2 points where the edges tuched the floor , we put 2 pieces of 20 mm wooden plates under it .
Then i stepped on the backplate and jumped a little , checking with another 20 mm test plate on other places of the edge and jumped again untill the test plate was fitting equal tide at all places . Final checking with 3 crosswires and again made small adjustments .
It was the part outside the backplate that was warped .
Just putting the dish flat on the floor would not help , the warping has to bend back trough a certan point , thats why i used those 20 mm plates .
 
Looks like there are several methods available to straighten out a dish. I used a brute force method by placing the dish on its back, stringing it and pushing down on the edges until the strings all came together. I know what you mean by going past the certain point, so that it snaps back to the correct spot.

Once the dish was up on the mount, I did what Huevos did by trying to adjust it slightly with it in situ and watching the signal levels. I think it's almost as good as it will get.

That's the problem with big aluminium dishes - they bend too easy. And the majority of them don't have a very good back support to stop them from twisting.
 
So how is it performing now?
 
Very well. I think it's pretty much back to how it was originally... Certainly much better than the CM I had. May want to try pull the arm up a little like you did as there's quite a lot of weight sat on it (1 Ku and 2 C LNBs).
 
It's partly pulling thr arm up but more pulling the top of the dish down. Push the arm up with a finger and see if it picks up signal. If not just leave it.
 
Yep, the signal did pick up a little! Maybe only 0.2dB but every little helps!

How did you attach the wire at the dish end - drill a hole at the top or...?
 
Saw this thread and thought I'd pop up to the roof to do the string test. The dish seems to be perfectly true, despite the ding it got in transport (now irrelevant due to the amount of bird shit there. While I was there I thought I'd connect the signal metre and do some experiments. I tried pushing the dish from behind at the top (so simulate the effect of Huevos' tenser wire). I also tried pushing on the rim from both sides. Whatever I did the signal dropped so I guess it's okay. In any case, assuming the dish is as it came out of the factory, you'd think that Gibertini would engineer the thing to place the LNB in the focal point with a tolerance of 2 or 3 millimetres (?). Unless it were damaged in transport or setting up modifications shouldn't really be necessary, should they?
 
I am guessing in mine and Huevos's case is there are 3 LNBs hanging off the arm - pulling the whole thing down. I don't get any signal increase with just the one LNB on it.
 
Captain Jack said:
I am guessing in mine and Huevos's case is there are 3 LNBs hanging off the arm - pulling the whole thing down. I don't get any signal increase with just the one LNB on it.
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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..
 
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