Attempting to use an unknown dish for FTA

Doorguru

Doorguru

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Does anyone know what kind of dish this is? Initially I thought it was a Slimline, but now I am not sure.

The dimensions are approximately 33 3/4" X 24". I am trying to find the focal point. I foolishly removed the 3 LNB's that were mounted and threw them away. I do remember they were segregated and had a multi piece removable fancy cover. Also this setup had a tricky name from either Direct TV or Dish Network. I think this dish might work better than the smaller ones I have saw of the same style for FTA. The LNB in the picture is one I calculated the position using a formula I found online. I have not tried it yet.

Unknown
 
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Doorguru

Doorguru

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Hold the presses! After posting this (of course), I did more research and found this to be a version of a DN Superdish. If anyone has a dish of this size (33 3/4" X 24") is it possible for you to measure the focal point?
 
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Doorguru

Doorguru

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Thanks! I hope it's not too much trouble for you . I was thinking of pasting some aluminum foil completely over the dish with flour and water and taking it out in the sun. It would probably get very hot though. I could probably find it without the foil. I would imagine on a dish like this there would be a row of focal points (?).
 
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a33

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Thanks! I hope it's not too much trouble for you . I was thinking of pasting some aluminum foil completely over the dish with flour and water and taking it out in the sun.


That would be a hard task, if you want to get a really precise outcome!
Measuring and calculating would be easier; even for a non-flat dishface paraboloid dish. I recently made a spreadsheet calculator for that, needing just 4 input measurements, giving exact dish specs on the basis of sound parabola-equations.

However this non-flat dishface dish of yours will likely be designed for multifeed reception, so the shape will not be paraboloid (parabolical both vertically and horizontally) as needed for the above calculation, but toroidal (parabolical in vertical dimension, circle-shape in horizontal dimension).
I haven't found an easy way to measure and calculate that, though.

So if KE4EST can give you the proper dimensions, that is the way to go!

Greetz,
A33
 
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Brct203

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Dec 24, 2016
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I have a dish that appear to be similar (DN Superdish). I have the original feed assembly on it (dual linear and circular for 119W and 121W, with stacked LNBs with flanges)

From the center of the plastic surface of the linear feed (square wave guide which is centered on the arm while 119W circular is a bit to the side), I measured 26 1/4 inches to the upper edge of the dish, and 20 1/2 from the bottom edge.

the same center of the feed is about 4 3/4 inches from the arm, measured perpendicular to the arm. That perpendicular line is about aligned with the single hole in the arm

I have used that dish with a LNBF and the same bracket as you are using, and found that the existing hole (the next one after the 2 holes that held the original feed) works well for attaching that bracket. You can see the mark left by that bracket on the arm on the picture below.

of course all this is correct only if it's the exact same dish. Only obvious difference is that mine has the DN Super Dish logo painted on it. See attached picture for identification. The feed assembly used to have a side bracket for a 110W LNBF

IMG 3941
IMG 3942
 
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a33

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From the center of the plastic surface of the linear feed (square wave guide which is centered on the arm while 119W circular is a bit to the side), I measured 26 1/4 inches to the upper edge of the dish, and 20 1/2 from the bottom edge.

And once you know dish height, top string and bottom string length, calculation of LNB-aiming point ("G-spot") on the dish is easy.
(That is where the bisector line between topstring and bottom string hits the dish; so it can also be done visually.)

Greetz,
A33
 
polgyver

polgyver

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I have similar, a little smaller dish, on my porch, (directed to Hispasat) which I use mostly to check various LNBF's, if they work.
Using alum. foil is a good idea, but an overkill regarding power : why to cover all dish?
This would bring a few hundred Watts to LNBF face. Much better is to use a few (3 to 7) small mirrors, 1/2" to 1" size, round or square, it is easy to get them from craft store. You could place the mirrors randomly on the dish, using double-sided thin glue tape, or other tape over the mirror edges. Stick a piece of cardboard 3"x5" on LNBF as a "screen".
If you use more small mirrors, you can see the difference of the focal "cloud" when you move the "screen" sideways from main focal spot, when turning the dish.
The reflections will be dispersed, some call it "coma".
I think this dish is typically, part of Paraboloid of Rotation, with single true focal spot.
Dishes, stamped from metal sheet, usually have flat dishface, as the dies used to form them are easier to be made this way.
With plastic dishes, their faces do not have to "belong" to a plane, and they can be designed to have modern, "cool" looks, like radar dishes.
But, as long, as they are cut off from one "mother Paraboloid of Rotation", they will focus to a single spot.
The photo of my porch dish is below :
Thumb IMG 5089 1024
 
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907TECH

907TECH

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Dishes are not that expensive, IMHO you are far better off with a purpose built single satellite dish. Unless you just want the challenge of seeing if it can be done. The gain will be higher with the proper dish.
 
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Doorguru

Doorguru

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Yes, I could just buy a proper dish, but as mentioned, I am doing it for the challenge. I already have a working FTA dish pointing at Galaxy 19. This property has no clear horizon. I had to cut down numerous bamboo trees to get that dish to work. Unless I get lucky, I don't think I will be able to use this project dish for anything other than Galaxy 19 due to it's size and especially due to the horizon situation. It was probably foolish to buy that Edision MIO, but I liked it's multi functions (WIFI, OTA). I just got it and haven't hooked it up yet. With my lack of knowledge, It's going to be another challange!!


I got home from work, grabbed the foil.. sprayed down the dish with WD-40. It made the foil stick to the surface pretty flat and only took a minute to do. I angled the dish to the sun and held a piece of paper by the end of the LNB mount. I could see that the LNB mounting will have to be past the end of the square tube, much like polgyver's very nice picture. My dish is a little larger, so I can't go by his dimensions. Oh course, it had to be overcast today.. hardly any steady bright sun, but I did get a general idea. If anyone attempts this, wear sunglasses to protect your eyes from being flashed when aligning the dish. I will ditch part of the generic mount I bought (the portion that bolts to the LNB arm) and make a longer one based on what KE4EST tells me. Hopefully he has the exact same dish.

Thanks everyone for you input!!
 
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Inclined Orbit

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You don't have to cover the entire dish with light reflective material, you only need a thin strip that runs top to bottom and side to side on the reflector since that will tell you everything. I've used a laser pointer and some reflective aluminum tape to repair a bent feed on a 2.4m dish on a satellite truck and it worked well but was very time consuming. Here is a method from a friend of mine that will find the focal point and also let you know if the dish is damaged or not suitable for the frequency range you are using. Dish accuracy checking with lasers ...de N6CA
 
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KE4EST

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I see Brct203 beat me to it. :) Sorry had a longer than normal day at work. Anyway, that is the same measurements I got. All the ones I have in my satellite dish junk yard though I notice have "Super DISH" across the face of the dish. I guess the one you have was in a different envorionment or made by a different manufacturer. How long is the rectangular support arm on yours Doorguru?
 
Doorguru

Doorguru

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You don't have to cover the entire dish with light reflective material, you only need a thin strip that runs top to bottom and side to side on the reflector since that will tell you everything. I've used a laser pointer and some reflective aluminum tape to repair a bent feed on a 2.4m dish on a satellite truck and it worked well but was very time consuming. Here is a method from a friend of mine that will find the focal point and also let you know if the dish is damaged or not suitable for the frequency range you are using. Dish accuracy checking with lasers ...de N6CA

Quite an interesting article! Looks like it wouldn't be that hard to set up.

I see Brct203 beat me to it. :) Sorry had a longer than normal day at work. Anyway, that is the same measurements I got. All the ones I have in my satellite dish junk yard though I notice have "Super DISH" across the face of the dish. I guess the one you have was in a different envorionment or made by a different manufacturer. How long is the rectangular support arm on yours Doorguru?

Don't be sorry! I appreciate your input now and in past posts.You have helped me a lot!

The proportions (Ht,W) on Brct203 's dish does not match mine. Based on his dimensions, it has a slightly different shape.

The total support arm length is 22 1/4 " , measured from the bottom rim to the very end. The arm length itself is 23 7/8". With my experiment today, I think I can get it in the ballpark. I will make the mounting bracket adjustable so I can slide it in and out. Same for the height. IF I can find a signal, I should be able to tweak it by looking at the signal strength.
 
. Raine

. Raine

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Be real careful covering the whole dish in foil. I and my daughter made a couple of solar cookers with dishes smaller than that one and at the focal point it could boiI water, burn wood, etc, real fast too.
 
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Brct203

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The proportions (Ht,W) on @Brct203 's dish does not match mine. Based on his dimensions, it has a slightly different shape.
I'm not sure that I understand what makes you think it's different...

the dimensions I gave were distances from the white plastic cover of the LNB Feedhorn to the edges of the dish (top and bottom). The reflector size is exactly like the one you have (33 3/4 wide by 24 tall). The arm rectangular tube is also like what you said (22 1/4 from the rim of the reflector, 23 7/8 total).
 
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polgyver

polgyver

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Checking dish's focusing with mirrors and magnets - another version
I am really puzzled, why this easy and simple method is forgotten by forum members, searching for unknown dish's focal spot.
Aluminum foil is worse than glass mini mirrors, as foil reflection is not well defined.
Using mini mirrors with magnets on steel dishes allows also for easy shifting of any mirror to different area of the dish, while watching if its reflection moves away or not from LNBF's face.
Of course, this method is entirely dependent on presence of Sun...
cheers, polgyver
 
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KE4EST

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The total support arm length is 22 1/4 " , measured from the bottom rim to the very end. The arm length itself is 23 7/8". With my experiment today, I think I can get it in the ballpark. I will make the mounting bracket adjustable so I can slide it in and out. Same for the height. IF I can find a signal, I should be able to tweak it by looking at the signal strength.
You sir have the same thing that Brct203 has. Same as mine. A "Super DISH" dish.
 
Doorguru

Doorguru

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You sir have the same thing that Brct203 has. Same as mine. A "Super DISH" dish.

I'm not sure that I understand what makes you think it's different...

the dimensions I gave were distances from the white plastic cover of the LNB Feedhorn to the edges of the dish (top and bottom). The reflector size is exactly like the one you have (33 3/4 wide by 24 tall). The arm rectangular tube is also like what you said (22 1/4 from the rim of the reflector, 23 7/8 total).

:oops: Oops!! My mistake.. I got my posters mixed up!! I was looking at polgyver 's post and the picture of his dish and got it mixed up with your post!! :oops: I even mention his nice photo in one of my replies.. I apologize for all the confusion..
 
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