I found an old win95 program for figuring out your own parabola.
That should be interesting.
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I found an old win95 program for figuring out your own parabola.
That should be interesting.
That 4 foot by 8 foot reflector I built was designed to fit on the front of 1 meter dish. I built an H shaped support with a bar running down the center of the H cross bar and that fit over the top of the dish and had a little dowel to fit in the lowest LNB support. The sides of the H had little bars to help keep the thing from moving side to side as well. All this out of 1 by 2 inch lumber. The up and down parts of the H had 15 degree angled wood supports (angle = atn(y / (2 * f))) That varied in height according to the basic parabolic eq x = y*y / (4 * f). 15 degrees was picked because it was something that I could do with a miter saw I have. One of my design errors was a too small focal length--I used 4 foot when I should have used something up above 5 foot. That would have moved the 15 degree supports out to closer to the end of the .25 by 1.25 inch 8 foot long wooden reflector surfaces that were flexed to shape by the supports at center and those 15 degree blocks and then by string at the end. Cost was only around $20 US for all the parts. Painting the wood took a while. Attaching the window screening to the wood took a while too.
Sort of worked, but I would think just using a jig saw and plywood to form the parabolic curved ribs would be easier. Easier than cutting out a Fresnel lens too.
I was thinking of the 1/2 inch plastic pipe that is easily bendable, to make a big spherical dish.
Still trying to figure out an approach with that.I think the only fittings available are t's and elbows.
PVC pipe can be steamed to make it bend just about any way you might need. Once did an extended cave trip with backpacks made of big PVC tube flattened to an oval shape to fit through the narrow parts. Many plastics can be bent/shaped/cut by heat applied right. Most plastics become brittle with time and cold temps.
I've thought that very thin sheets of something like plywood or wood paneling might be an interesting place to start with DIY dish. I even like the idea of using cardboard--I've seen burning man "tents" made from cardboard and they have built canoes out of cardboard w/ protective "paint". Not saying that you could leave it out in tropical rainfall, but in some climates it could be left out for most of the year. I also like the idea of modular dishes--say three modules that have octagonal or 12 sided that attach to each other to make up a dish. There are big telescopes that use a similar idea as well as large solar furnaces with hundreds of modules--usually they use hexagons with spherical reflective surface and then either flex the module to a parabolic shape or just position it to reflect to a single point as if it were an element of a parabolic surface. I took the idea of sub-dividing a geometric shape like a square or triangle and mapping (on PC) the new points to a sphere and then tried mapping to a parabolic surface--cool looking images--it is likely "tessellation" to the math guys.
I'm not sure that spherical dish is any easier to build than a true parabolic dish. I know you can move LNB around in front of it rather than try to move whole dish, but you can make a very light weight dish and might even be able to mount it on one of the bigger provider dish mounts (think of the newer DTV oval ones).
I was thinking 1/2 inch plastic pipe which is floppy,the "fittings" I could make out of blocks of wood drilled out.
The 8 ball spherical dish of the 1980's was a 30 foot radius,so you use a 30 foot wire or chain with a pen at the end to get the curve on a piece of 2x12 or 2x14 to get the curve you need.
Still thinking about the umbrella dish in my other thread.
I found 1/2 inch plastic fittings from an old screen house,it had a 4way piece I might be able to use.
I've played with sphere too on Ku size dish. The focal points for sphere are half-way between surface and center, so 30 foot radius would have focal points on the curve 15 feet from surface. I usually think about just trying for a single satellite even with sphere and for the standard f/D ratio that means you only need about +-30 degrees of arc from center--at the focal point that means the LNB will see about 80 degrees surface. I would think 90 degree Ts would be all you need--at the top and bottom you can use straight-line segments between curved pipes with an occasional straight line between top and bottom to fix the curve's shape.
It is kind of hard to attach reflector to pipes though. Unless you just use a glue of some kind. There is an easy-ish way to shape the reflector to fit a sphere (just like the way they cut up globe into segments to fit on flat map)--cut out parts of flat sheet so that when edges meet they would form sphere (there are origami examples of how it works--look for "origami sphere 16 flaps"). I could post equation. The amount you remove for +-30 degree arc is very small even on 30 foot radius scale.
If you use the idea of bending back the parts of flat sheet that are not needed for spherical reflector surface and use a stiffer material like that they use for fencing or inside cement, then you could build a self supporting dish. IMO
I am not sure what dish is used but let me share a photo of 1 of my dish.
It's a Channel Master 6' OFFSET I use for C Band, right now is on 58west, I haven't clean it nor paint it yet, I use Titanium LNBF it really helps, I don't have Prime Focus yet all my antennas are OFFSET. Try to upload a photo of your dish it might help us help you.
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I believe the lnb placement was a pain.like you say 15' away but it did have the advantage of using multiple lnb's at the same time.
I would probably go rectangular shape with either windows screen(if you can still get aluminum) or hardware cloth.
My 1 meter is just the standard channel master 1.0.
It is an OFFSET dish then? If so you will need the Conical Scalar Ring, Flat Scalar Ring don't work with OFFSET dish only for Prime Focus dish.Quote:
Originally Posted by zelig
I also have a metal 5.2' dish aimed to 40.5 west.
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In first post he said he has conical scalar, but I have same dish and the flat scalar works just fine with it (well one of the two I have works OK--one of them does not have deep enough rings). And yes I have tried conical scalar too.
On the spherical reflector--I don't think I would try for a 30 foot radius--maybe 15 foot as that would put the focal arc at 7.5 foot and you would not have to make it soooooo big. Remember the whole chunk of the sphere you build still has to be pointed up toward the satellite arc in the sky, or you have to have a really tall post to put the LNB on--or both.
tomorrow is tree trimming day,so I may be able to attempt the 1 meter again.
In the experiments years ago I only had the flat scalar and I was able to get 121w or 123w,but I will stick with the conical.
When is an OFFSET dish with C Band it is never easy, minor adjustments and you gain some TPs but looses other TPs, there are some How To in forums for C Band on ku dish and they all say to aimed dish without scalar ring and once you have found the SAT then install the Scalar Ring to better signal quality, my friend CPR can tell you what a headache is this C Band on Ku Dish,
Conical Scalar Ring has it's tricks to, to far back or to far to the front, it all afffects the signal quality, also the LNB on the Bracket back or forward, and unless is Sat 40.5 the Skew is also factor.
In my location the Caribbean I can't get any C Band signal on a dish smaller than 5.2 feet, and for example the SAT 40.5 without Scalar Ring I only get 1 TP and with Scalar Ring I have 10 TPs.
I was watching a home improvement show yesterday and saw something that might be of use in DIY dishes. They made a "form" for an outdoor walkway with what they called "fiberboard"--no paint, they just cut it and bent it as needed, nailed it to stakes to hold it in place. There is something called MDF Bender Board (Common: 1/4 in. x 3-3/4 in. x 97 in.; Actual: 0.25 in. x 3.375 in. x 96 in.) that might be what they used but I'm not sure. The walkway was very curvy and seemed like the stuff is thick enough and wide enough to easily be used for a big dish.
I've used the 'bender board' before when pouring sidewalks. What I used came from H Depot and was really durable and plenty bendy. I guess it could be used for a dish...
I'm still playing with the math, but was thinking if one built a set of 8 parallel boards (or more) and joined them at top and bottom with both screw and glue. Then at the middle attached them to a third board with wider spacing than at the top and bottom then the whole thing might bend into something very close to parabolic or spherical shape--say 80 inches Top and bottom and full 8 feet at the middle with the expectation that the radius (if complete sphere were built rather than just a cap) would be around 8 feet and so the focal point around 4 feet and f/D ratio around 0.5
Sounds like a plan
You can visualize it by thinking of a globe of the world--just picture 30 degrees north and south of the equator and a chunk from 30 degrees one side of a longitude to 30 degrees on the other side. You are forcing the 8 foot length to be the equator line and the parallel 8 foot lengths are the longitude lines. It is the same idea as a "stress beam" dish, so the same limitations apply--things do not really form a perfect needed shape if just a few points of stress are put on them, so some other forces have to be put on the beams to get them closer to the shape you need.
I did a 1/12 scale model to test the idea out. Used a pressboard cracker box for 8 inch by 1cm "board". Re-locatable spray adhesive on top and bottom with 0.8 inch to center separation and then put in equator with 1 inch to center separation. I first thought that it really did not work well at all, but then realized that the top and bottom boards needed not to be glued and they need a wedge to set the angle. The glue kept the boards from rotating and put too much strain on the equator, so it bent up too much--I eventually got the spray adhesive to let the torque happen.
The overall dimensions ended up 7.9 inch by 7 inch tapering down to 5.6 inch, with center raised 1.75 inch if you put all four corners down on flat surface and pressed equator a little (0.75 inch across 3.5 inch and 1 inch across 4 inch dimensions as needed by f=4 and parabolic eq).
Those wedges will be easy to create out of cardboard flaps, not sure yet how to do that with MDF boards--maybe metal bent up.
Here is pic of the latest scale model. Still 8 inches by 1 cm 'boards'. Wedges are 26.5 degrees, so 0.5 cm tall at outer edge and largely remove the S curves I was getting in the first attempt. I doubled the equator board width as it seemed to be getting too much force from the outer two boards. I did hot melt glue in the boards to the outer boards (longitude lines cross lats at right angles).
Seems to need to be stressed toward the equator by 1/8 inch or so to get the right heights (maybe use lines from outer corners to opposite corner? maybe leave out glue on the outer boards and tension everything to the right shape and then bolt it tight to that shape?). Spacing is 27 mm at equator and 23 mm at outer boards (I was shooting for 0.866 ratio and using as much of the 8 inch equator board as possible). Overall it is about 7.25 inch by 7.75 inch without extra stress.
I am going to attempt the mini bud again tomorrow.
I cut some bushes and can get a good ku band signal on 121w and 125w
wasted all day on 121w,the receiver would do a blindscan and pick up 1 tp at a time but not consistently.
I did detect 3 tp's but not enough to assist in aiming.
Finally swung around to 91w,I had the pole marked for 91w ku already.Elevation is 4 degrees higher than ku,this I remembered from 10 years ago when I did an experiment just strapping an lnb on to the existing 3 armed primestar 1 meter dish.
conical scalar isn't critical,it all depends on if the lnb is pushed all the way forward or all the way backwards.
I did try it on the very edge of the lnb and again pushed in so the outer part of the lnb formed the final ring.
I didn't see any performance difference.I am actually using a flat scalar from the 1980's on it now.
For a novice I would aim a dish ku for 91w and go for that one 1st with a c band lnb.
The one I am using now is a kludge with the ku portion ripped off and replaced by copper foil.My holier than thou lnb.
for aiming 3820v 30000
quality is 70% which is better than some of the ku sats i get.
Clear sunny day out.
Lnb arm is ripped off a 80cm dish and mounted on the wrong side of the dish but still works good.The original was a 3 armed 1 meter primestar retailer dish.
I actually get a couple of dvb-s2 tp's,if lyngsat info is correct.
3740v
3966v
I will drag a tv and receiver out to the dish tomorrow and try to tweak with the conical scalar installed.
the only sat I can get is 91w with an eirp of 43 in my area.
107w I can get about 20 channels but only a few watchable due to pixelation.
That has an eirp of 42
So I can say if the sat has an eirp of 42 or less you can forget about it.
I was getting dvb-s and dvb-s2 tp's before the clouds rolled in,if the lyngsat info is correct.
the flat scalar from the 1980's is 6.5" diameter.
The modern scalar that came with the lnb is 6.25" as is the conical scalar.
I have the flat scalar from the 1980's on it now, flush to the end of the lnb and I get 24 channels on 91w even in heavy rain.
3820v quality is 70%
I can get 1 tp on 34.5w
4127h 3679
but it only has 3 channels so I didn't stay there long.
circular polarization, so you have to put a dielectric plate in the lnb throat.