7 laser illuminator with 14 small mirrors reveal Wavefrontier flaws

[polgyver]

I bought the Wavefrontier 90 quite a long time ago, really cheap, as it was offered without LNBF holders and it had its top badly bent. I straightened the top, but the dish did not perform well, as the Q was below expectations. The string test was OK, so, more "digging" was needed to find, why?
As the small mirrors test is dependent on Sun's presence, and the Sun moves constantly, testing a dish with double reflector is not easy.
Therefore I got this idea to build a laser illuminator. And, after test, it is clear that not only the top, but also all upper part of the dish is distorted.
Annotated pictures follow.

 

[Dee_Ann]

You are brilliant! You should be working at NASA or something ! WOW!

 

[lost_mesa]

Great project polgyver. Amazing!

 

[Joe DC]

Very ingenious! Are the laser beams all parallel with each other? If off slightly might that cause a final alignment error?

 

[jorgek]

Another excellent project!

 

[Cosmo Blatz]

Impressive!
Obsess much?

Can't wait for the polgyver build-your-own backyard particle accelerator project !

 

[scarecrovv]

Nice to see you putting your OCD to good work LOL. Nice work....Been meaning to try your "tiny mirrors" project... Got the disco ball bought already.

 

[polgyver]

Very ingenious! Are the laser beams all parallel with each other? If off slightly might that cause a final alignment error?

The beams are parallel; I used sort of a "mask" (two pieces of cardboard, joined with duct tape) placed close to the lasers, and marked the laser spots. Next, moved the "mask" 170 cm away, and, using 4 screws on each laser, brought the beams to shine on the marked spots.
With such a distance, one degree spans 3 cm, and I was able to point the beams with better than 0.3 cm accuracy, therefore the beams are parallel with error of 0.1 degree,
I like to cut corners and simplify, but parallel beams was crucial for this project.
More error was introduced by these tiny rare-earth magnets, (I bought them from e-bay, one hundred cost me about 12 bucks),
as some of them are not exactly parallel - or, maybe the double - sided tape attaching mirrors to them, was not evenly thick?

The original aim of this project was to avoid scorching Sun, and have the Sun imitation stopped (sort of copying biblical Joshua).
Also watching, how the focal spot changes when dish is "off-axis" - and if there could be built special feedhorn, or scalar, able to "catch" the signal - even with strong "coma" distortion.

BTW, thanks for words of appreciation to all thread posters
Cheers, polgyver

 

[Cham]

Are you able to modify the top of the main reflector to cause better focus? Maybe it would be easy to pop it back... Have always been interested in these cassagrain style dishes but would have liked a larger one than the ones more commonly available, and shipping damage would be difficult to avoid as the surfaces are more critical than the normal offset reflector dish.

 

[N0QBH]

Great work and very informative - thanks.

 

[polgyver]

Are you able to modify the top of the main reflector to cause better focus? Maybe it would be easy to pop it back... Have always been interested in these cassagrain style dishes but would have liked a larger one than the ones more commonly available, and shipping damage would be difficult to avoid as the surfaces are more critical than the normal offset reflector dish.

Sorry for delay in reply. Yes, I would like to modify the dish so it could be returned to service. However, more tests are needed. Of my seven lasers, five have been damaged by rain, only 2 work. I am not sure, how to "pop" the top of the dish.
Another thing which confuses me, is the fact, that this dish passed very well the 2 - string test - the strings barely touched each other. Months ago, there was a post by other member, Rima from Latvia, where he reported the same dish tested with 2 strings - the strings were 2 cm apart (!) - yet he was able to receive many satellites. The edges of primary reflector of this dish seem to belong to a plane, not to a curved surface, what is the case with internet Blueberry dish.
For now, things are now on "back burner" until I find more time to continue. Cheers, polgyver