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For those of you wanting to play with parabolic LLPRs and Dishes.. I threw together a cheap and dirty spreadsheet this morning to plot various parabolic curves. I haven't validated the calculations but I'm pretty certain they are good.
You'll find it handy for verifying the parabolic properties of objects (old kitchen utensils etc) that you may want to try and use as parabolic reflectors.
By taking just two measurements, diameter and depth, you can plot a parabolic curve and then print it to use as a template to check the object.
You can also play around with different focal lengths and diameters to get a feel for gain and size if you're interested in building from scratch..
Special notes..
The curves require very little input.. basically diameter and focal point or depth.. if you don't know the focal point I provide a means to calculate one based on the depth of the dish.
When printing the curve out make sure the x and y scales are square.. I noticed excel likes to alter one of the 2 axis which can distort the curve.
If you need to print a curve larger than a 8.5 x 14 you can export the curve out to another program like corel which will print the curve across multiple sheets of paper which can then be taped together and used as a template for your larger projects.
Let me know if you find any errors with the calculations.. I'm not that talented with spreadsheets..but I think you'll find it gets the job done.

NOTE: Found and fixed a problem with depth to focal calcs in version 1.00

[color="Blue"]Parabolic dish calcs v1.01 click here[/color]


..

Good work.. Stickyfied...
If you update the spreadsheet, just edit your post, and reattach the new file.

Dutch

If you have any changes or enhancements you want to contribute to the spreadsheet feel free to do so and please post them.

For you MacGyvers, here's a few tips you might find handy when shopping for parabolic utensils..
1) Visit you local 99 cent store at least every 2 wks. The one near my office rotates stock pretty frequently, and I've always managed to walk out with at least $5 worth of stuff, serial to USB converters found in PDA synch cables, 4v miniature lead acid batteries contained within rechargeable flash lights, dc to dc voltage converters within has been cell phone chargers, 120vac to dc adapters and all kinds of cheap tools which can be modified for special uses.

2) When shopping for parabolic utensils a laser pointer, ruler and a strip of metalized Mylar (like found on the inside of you favorite potato chip bag) work really well.. I simply put the ruler in the center of the bowl as if I'm measuring the depth and then point my laser at the sides of the bowl making sure to stay perpendicular to the top of the bowl. You should see the reflection stay pretty much stationary on the ruler (1cm of wobble is okay) as you move the laser from the edge to the center of the bowl. Most bowls will become non parabolic at their base as they flatten out, which is ok. If the flatten area is small, It shouldn't have much impact on overall performance. I found 9" stainless steel mixing bowls at my 99 cent store which was about 75% parabolic. Use them like a hybrid Cassegrain/reflector. The Mylar comes in handy for plastic ware. Just build up a static charge on the Mylar and lay it down the inside of the bowl to produce a reflective surface to bounce your laser off..

3) Plastic ware tips. If you find something in plastic you want to use, simply line it with foil wrap or I prefer to use the 2" wide foil duct tape.

Scruge wrote:...
3) Plastic ware tips. If you find something in plastic you want to use, simply line it with foil wrap or I prefer to use the 2" wide foil duct tape.

Another good one is "3M Auto Body Tape". It is extremely heavy-duty aluminum tape with a permanent adhesive backing. The width is usually 2" in the standard roll, and it is probably double the thickness of HD aluminum foil.

Those of use that live in climates where salt is needed on winter road surfaces know about it. It allows you to patch major holes in car and truck bodies and make it through inspection without the expense of real body work.

Thorn wrote:Another good one is "3M Auto Body Tape". It is extremely heavy-duty aluminum tape with a permanent adhesive backing. The width is usually 2" in the standard roll, and it is probably double the thickness of HD aluminum foil.

Those of use that live in climates where salt is needed on winter road surfaces know about it. It allows you to patch major holes in car and truck bodies and make it through inspection without the expense of real body work.

Riiiiiiiiight.... And it has nothing to do with the low native population of guineapigs and hamsters in your state ??!?

Dutch

Thorn wrote:Those of use that live in climates where salt is needed on winter road surfaces know about it. It allows you to patch major holes in car and truck bodies and make it through inspection without the expense of real body work.

What about bumper stickers, (automotive body bandages)

Any chance of a more detailed explanation of importing and plotting the curve in coreldraw? The reason behind this is an old Dish 500 satellite dish i have lying around I love to be able to use for wifi purposes.

waytostoned wrote:Any chance of a more detailed explanation of importing and plotting the curve in coreldraw? The reason behind this is an old Dish 500 satellite dish i have lying around I love to be able to use for wifi purposes.

Your google foo is weak grasshopper.

Use the google.. Lots a stuff on old sat dishes modded for 802.11b

Even a few links on this forum!

waytostoned wrote:Any chance of a more detailed explanation of importing and plotting the curve in coreldraw? The reason behind this is an old Dish 500 satellite dish i have lying around I love to be able to use for wifi purposes.

Search on "primestar".

Airstreamer wrote:Your google foo is weak grasshopper.

Use the google.. Lots a stuff on old sat dishes modded for 802.11b

Even a few links on this forum!

Currently, I am waiting for SBC to get off their butts and activate my DSL. Until then, all I have is dialup. Anyways I found alot of primestar links, but none for round DSS Dishes...

I didn't think the dish 500 was round. I knew the single lookers were round but I think mine (dish 500 dish) is slightly elongated. Now that I think about it I think it is round just a larger diameter. I have just found some info that says the "mostly-round 20inch DISH 500 reflector". You may have some serious math to do.

wrzwaldo wrote:I didn't think the dish 500 was round. I knew the single lookers were round but I think mine (dish 500 dish) is slightly elongated. Now that I think about it I think it is round just a larger diameter. I have just found some info that says the "mostly-round 20inch DISH 500 reflector". You may have some serious math to do.

Most of the DSS and Primestar dishes are an "offset focus".
Take a look at:

http://www.wwc.edu/~frohro/Airport/Primestar/Primestar.html

Edit:

Dish 500 is a multi focal point dish. Two LNBs side by side at the focus point(s) of the two birds it's pointed at. Large multpoint dishes have a parabolic curve in the vertical plane, and spherical in the horizontal.

Airstreamer wrote:Most of the DSS and Primestar dishes are an "offset focus".
Take a look at:

http://www.wwc.edu/~frohro/Airport/Primestar/Primestar.html

Edit:

Dish 500 is a multi focal point dish. Two LNBs side by side at the focus point(s) of the two birds it's pointed at. Large multpoint dishes have a parabolic curve in the vertical plane, and spherical in the horizontal.

Finally someone is beginning to understand my dilemma. Yes, the dish is in fact a multi focus point dish. That is why I am scratching my head, somewhat confused.

I also have an older smaller round Dish network dish, maybe I should just use that instead? I believe that one is perfectly round.

I did find this link here inside the forums, http://netstumbler.org/showthread.php?t=16177
That is about as close as I can find here on the subject besides Primestar dishes. I guess I can just wing it, and do my best to find it, manually making fine tune adjustments and comparing results, which would be very time consuming. Rather not have to go this route if at all possible...

waytostoned wrote:Finally someone is beginning to understand my dilemma. Yes, the dish is in fact a multi focus point dish. That is why I am scratching my head, somewhat confused.

I also have an older smaller round Dish network dish, maybe I should just use that instead? I believe that one is perfectly round.

I did find this link here inside the forums, http://netstumbler.org/showthread.php?t=16177
That is about as close as I can find here on the subject besides Primestar dishes. I guess I can just wing it, and do my best to find it, manually making fine tune adjustments and comparing results, which would be very time consuming. Rather not have to go this route if at all possible...

Yes the older dish is round. I would use that just for simplicity in focusing it and it should still give great gain with the proper element.

wrzwaldo wrote:Yes the older dish is round. I would use that just for simplicity in focusing it and it should still give great gain with the proper element.

Build it just like the Primestar dish. The Dish 500 is designed so a satellite off to the right of center focuses out to the left of center after it bounces off the dish. Satellite to the left of center, goes to the right. Guess what happens to the signal from the bird that is dead center?

Bingo! Goes straight out. The focus is not quite as sharp as a true parabolic, due to the "spherical-ness" of the curve introduced to make it a multi-focal dish.

A bit more:
The dish 500s' have a 'skew' adjustment so the apparent (at least to us on the ground located North or South of the equator,) geosync arc can be compensated for. The dish is actually rotated slightly because the sat at 119 is slightly lower to the horizon than the one at 121. (Where I live. The skew offset will be different for folks in the other parts of the country. Your mileage will vary.)