Mini mirrors survey dish's geometry, locate focal spot
- Thread starter polgyver
- Start date
- Latest activity Latest activity:
- Replies 16
- Views 3K
- Status
Think you need more mirrors, then you can cook your breakfast! 
Reminds me of an electrical engineering students' project I had a look at a few years ago, they had what looked like a 10' dish with hundreds of 2" round mirrors glued onto the surface. They were working on high performance photovoltaics, but I wonder what else they "melted" with it... The round mirrors worked well in the parabolic backing, but smaller square/rectangular mirrors should work too, as evidenced by the last photo.
Keep warm!
-C.
Reminds me of an electrical engineering students' project I had a look at a few years ago, they had what looked like a 10' dish with hundreds of 2" round mirrors glued onto the surface. They were working on high performance photovoltaics, but I wonder what else they "melted" with it... The round mirrors worked well in the parabolic backing, but smaller square/rectangular mirrors should work too, as evidenced by the last photo.
Keep warm!
-C.
That's a pretty good idea. I've often stood in front of my BUD and wondered what it would be like to see the focal points of all the satellites across the front of the dish. Wouldn't it be easy to fine tune one if that stuff was visible?
I'll put this in my memory bank and maybe revisit it after the spring thaw.
I'll put this in my memory bank and maybe revisit it after the spring thaw.
I have done similar mirror experiments after having read your previous postings. Not to take anthing away from your insightful and meticulous trials, is it not enough to just place mirrors at the 12, 9, 6, and 3 o'clock positions and one in the center of the dish. If they all focus in a tight cluster onto the LNB surface then is it safe to assume that the rest of the dish surfaces are also in proper alignment?
slightly off topic but I wonder if a fresnel lens from an old projection tv could be used instead of a parabolic reflector and what reception would be like compared to a similarly sized dish
I have an artical from 1985 that used a wooden fresnel lens for c band. It was made from 2 4X8 sheets of plywood and had the gain of a 6-8' dish.
It would be fun to try to make one for Ku.
It would be fun to try to make one for Ku.
made a superdish mod last year where we painted it a bright yellow, set up a light 60 ft away and looked thru the lnb mount as we adjusted the dish to see the light.
The whole face of the dish lit up really bright when the dish was aligned on the light. I have to admit how bright surprised me. we did this so we could build a sight on the dish to get his house with internet easier. Worked fair and the internet is still working well.
The wife was unhappy with the bright yellow dish pointed at the neighbors house so we repainted it grey again.
anyway, there was a slight bend in the middle of the dish that stood out like a sore thumb with the light on it. you would never be able to see the imperfection otherwise.
The whole face of the dish lit up really bright when the dish was aligned on the light. I have to admit how bright surprised me. we did this so we could build a sight on the dish to get his house with internet easier. Worked fair and the internet is still working well.
The wife was unhappy with the bright yellow dish pointed at the neighbors house so we repainted it grey again.
anyway, there was a slight bend in the middle of the dish that stood out like a sore thumb with the light on it. you would never be able to see the imperfection otherwise.
Good question. Five mirrors which you used can locate the focal spot (useful, if the LNBF bar was missing or damaged). For positive verification of correctness of paraboloid, even 19 mirrors (which I used) would not be enough. This could be seen on the following photo. About 2-3 years ago I was experimenting with Seesat dish.
When it got dark, I hauled out a 500 W halogen lamp.
And this can also be confirmation of Kodaz observation : when light falls at sharp angle, irregularities become visible.
The dish's bracket was made of sheet metal much thicker than the dish's "bowl". The bracket was NOT shaped properly, and when the four carriage bolts were tightened, the bracket "won", thus distorting the dish's surface.
In daylight, not very noticeable.
Obviously, the four distorted areas do not return the waves to the LNBF. And, small mirrors, if not placed on these areas, would not "report" that something is wrong.
_very_ cool. This sounds like a really fun experiment. I found some more information that I don't entirely understand yet here: http://www.microwavejournal.com/ext/resources/pdf-downloads/Recent-FZPA-Advances-ssg-submission.pdf
one of those fresnel dishes would be good for
a) somebody good at fabricating stuff that hasn't been able to salvage a c-band dish
or
b) somebody with uppity anti-dish neighbours. "that's not a satellite dish, it's a piece of modern art"
a) somebody good at fabricating stuff that hasn't been able to salvage a c-band dish
or
b) somebody with uppity anti-dish neighbours. "that's not a satellite dish, it's a piece of modern art"
On Nov. 19, 2013, primestar31 posted (#8) this article from Radio Electronics, (and this article is 29 years old... ) where its author ALSO included corrections of mistakes in this article. Most important, the efficiency of Fresnel dish would be just 15 dB, whereas same size paraboloid dish - 37 dB. Not worth bothering ...
Thread title : North America BUD production
Last edited:
A 2x4 placed where the frypan is here, cooking and egg,
would scream in a second and burst into raging flames.
It appears that the concentrated 'rays' are boiling the humidity in the air just below the pan
Yes, the actual focal point is below the pan bottom. Just think, if I'd modified it
just a bit to get it 'right on' the pan bottom, youch.
would scream in a second and burst into raging flames.
It appears that the concentrated 'rays' are boiling the humidity in the air just below the pan
Yes, the actual focal point is below the pan bottom. Just think, if I'd modified it
just a bit to get it 'right on' the pan bottom, youch.
here all this timei been grilling on a gas grill, sheese
How often did you have to move the dish to refocus the sunlight?
How often did you have to move the dish to refocus the sunlight?
Last edited:
- Status
Similar threads
