SMW OA 1600 dish

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Interesting @rayhan , tell little bit more how you've made this dish. I would say, that skewing of the dish is necessary to get maximum performance.
Yes, there's a few things that I am curious about:

1) how do you make the dish reflective? Did you embed a mesh (CM/Prodelin style), or is there metal partiles or paint in one of the layers (SMW style)?
2) at what LNB positions do you get reception? At the ends, or in the middle of dish?
3) how did you calculate the torus-shape, and is the dish parabolic or circular in the vertical plane?

You can skew the dish by skewing the plate the mounting triped is screwed unto.
while not ideal, you can, for experimentation at least, put concrete blocks or similar under two part of the wooden plate, and thereby skew the dish.
Remember, the dish needs at the center needs to be skewed to be aligned with the sat arc across the sky.

Edit: Probaly the best approach is very similar to to find the "middle sat" for the dish, (which is somewhere in the middle of the 40 degree span you are looking for), and then align the left or right hand side of the plate with than direction. By tilting the plate either left or right, you can skew the dish, so that it's aligned with the geostationary arc. This would be clearer with a drawing, and I may make one for you if necessary.
 
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rayhan

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DIY toroidal
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Vadodara, India
I made a CAD model, got it machined on a CNC router on foam. Then used it as a mold to build a fiberglass dish. Between the layers of fiberglass, I put a layer of aluminium foil (the one used for packing food, available at grocery stores).
The dish is parabolic width wise and circular length wise.
I get reception at both the ends of the dish for both the satellites. I haven't tried the middle position but I don't think there is any reason why it won't work.
Correct me if I'm wrong, but as far as I understand, skewing the dish is done to compensate for the elevation difference between the satellites.

Here is what I'm trying to do:
1. Place one lnb at one side and align it toward 93.5E (GSAT). Once I start getting reception, I tighten the bolts to fix the azimuth of the dish.
2. Place another lnb at the calculated position for the second satellite. I've found the exact positions using my CAD model. Now, if I change the elevation of the dish, at some point I should start getting reception for the second satellite. However, I'm unable to do so. I've tried moving the lnb with my bare hands too. No reception for the second satellite anywhere.

I believe my lnb holding mechanism isn't as accurate as it should be. I'm trying to replicate the smw 1600 lnb holder but that is a time consuming task.

On a side note, I found that on a regular paraboloidal offset dish (60 cm), I can compensate for the error in alignment of the elevation of the dish by moving the lnb itself. As an example, consider I have reception at 60 degrees elevation. Now if I intentionally change the elevation to say 70 degrees and move the lnb upwards by 5-10 cm, I'm still able to receive almost the same signal strength. I've tried this with my torus and it works. This made me believe that there isn't a need to skew the torus at all.
 
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a33

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Nice thing you have fabricated! :)

I'm a bit worried about the 40 degrees azimuth difference you want: that is a lot, even for a torus dish, i would say.
The SMW OA1600 covers 26 degrees, I understood.
Are they both strong satellites?

How did you calculate the location of the second LNB for your dish?
At what point did you have your first LNB at that time? (I guess at another point than in your photos?)

PS. I hope with 'almost the same signal strength' you mean 'signal quality'? That is the important one...

greetz,
A33
 
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rayhan

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My Satellite Setup
DIY toroidal
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Vadodara, India
@a33 The satellites that I'm trying to capture are at 93.5E and 74.9E. That makes a satellite span of about 20 degrees.
The satellites I'm trying to aim at are strong satellites.
To calculate the location of the second lnb, I used my CAD model. However, since the lnb clamps have degrees of freedom in all the planes, it is very difficult to make sure the lnbs are at the right place. Nevertheless, I've tried all possible positions. I've tried moving the lnbs and aligning the dish for hours (5-6 hours).

Both the lnbs were at opposite ends of the dish. The second lnb was near to the second clamp (refer previous photos attached by me).

@RimaNTSS I see that you have a lnb clamp holder similar to mine. Could you please elaborate how you positioned your lnbs?
 
RimaNTSS

RimaNTSS

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I see that you have a lnb clamp holder similar to mine. Could you please elaborate how you positioned your lnbs?
Unfortunately, from your pictures (resolution is not enough) I do not see details of your LNB-holders, but that does not matter. You should always locate LNB in such a way that there is maximum signal. But..... First you should position one LNB directly in the middle of your dish, in it's Focus and point antenna to central satellite, which can, in your case be 85*E or 83*E. Then skew whole antenna (this is very important point) about 13* to East. In this position get the maximum signal on your central LNB. After it is done, find the proper place for your most East and most West LNBs, which are 93,5*E and 75*E. That is it. Use satlex.us calculator ScreenHunter_71 Sep. 29 08.38.jpg That all will work if you have made your dish in perfect shape.
 
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The dish is parabolic width wise and circular length wise.
I get reception at both the ends of the dish for both the satellites. I haven't tried the middle position but I don't think there is any reason why it won't work.
Correct me if I'm wrong, but as far as I understand, skewing the dish is done to compensate for the elevation difference between the satellites.
If I understand you right, your dish have vertical paraboloid profile, and horizontal circular profile. You should therefore be well off as you will end up having roughly same configuration as the OA-1600.

But I do think it will be essential to build in a mechanism that allows for skewing the dish.

The reasoning goes something like this:

1) A Prime Focus dish is parabolic in all planes, including what will be horizontal and vertical once mounted.

2) An offset dish (technically an offset Prime Focus dish) will (should) still be parabolic in all planes, both in vertical and horizontal plane, except that the reflector is now tilted a bit (most often in the vertical plane). But it is still parabolic as seen from the LNB.

3) A true toroidal dish is *not* parabolic in any direction, instead is it circular in both horizontal and vertical directions. Luckily, circular is an approximation of parabolic when looking a low angular sections of the parabolic curve. The circular dish does not have a single focus point, but still a spatial region of increased amplification (in which the LNB can be placed). This allows a toroidal dish to work, as it will perform only somewhat worse than a a true parabolic dish.

4) I believe the OA-1600 is a hybrid, with a parabolic vertical profile, and a circular horizontal one. This means that the dish has a horizontal focus line (rather than multiple focus points). This is a direct consequence of the dish having a circular horizontal profile. (This also means the performance is not as good as a dedicated single-focus-point dish.)

5) Ideal placement of LNB is:
a) vertically in the parabolic focal point, and
b) horizontally so that the LNB is pointing at 90 degrees to the surface of the dish. Note that since we have a focal line, rather than a focal point, you can still get reception when pointing at, sat, 85 degrees at the dish, but you will get max performance at 90 degrees.

The above points have an impact on your set-up without skew of the dish. Let's assume you have the dish horizontal (as in your pictures). This meanst that the LNB at the center of the dish, you will have best possible reception at whatever sat your aim at.

If you place an LNB at either end of the dish, the parabolic section is no longer pointing in the direction of the SAT (due to the arc of the sats). Seen from the direction of the satellite you are trying to receive, the reflector is not a true paraboloid viewed spot on, so your focal point is now also a focal cloud in the vertical direction.

With strong sats you may still be able to receive something, but it's far from optimal. And the problem is bigger the further from the "true" parabolic center of the aligned dish.

If you struggle with getting a feel for the focal behaviour of the dish, you can visualise it quite vividly by getting hold of some reflective tape, or even carefully applied kitchen foil (that you have already used in he build).
Carefully attach this to your dish in the vertical and horizontal directions (but only cover a small section of the dish!), point the dish *at the sun*(!), and hold a coloured piece of paper where the LNBs would go:

DishReflTape_1.jpg DishReflTape_2.jpg

( Taken from slide 20 of http://www.ntms.org/files/Nov2015/Fun_with_Off-set_dish.pdf )


Recommendation

SO: to get the most from your dish, I believe you need a mechanism for skewing the dish. If it is not heavy, it can literally be two plates with a central bolt that allows rotating the dish around the geometric center, and mounting one plate on the dish and the other on the mount.

Principle can be seen here in the mounting bracket for my WaveFrontier T55:

IMAG3165cut.jpg IMAG3160cut.jpg

At the same time, I would attach the feed-arms mechanically to that back plate, in the same the OA-1600 has them. This will remove most of the load on the reflector that might distort the surface of the dish when putting a number of LNBs on the feed-arms. Distorting the reflector even a little bit can be detrimental to the performance (as eg @John has found out with a Gibertini 125 elsewhere on this site):

Just Sharing This - 1.2 Precision / Octagon lnbf mod

And while you are in the metal workshop, you can be inspired by John's image in the post above and consider putting in a support rod from the plate attached to the reflector, to near the top or bottom of each of the ends. This will address the lack of rigidity you mention earlier, and limit unwarranted twisting in the reflector in high winds.

Best of luck with the project!
 
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a33

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5) Ideal placement of LNB is:
...
b) horizontally so that the LNB is pointing at 90 degrees to the surface of the dish.
In addition to this:

Remember that a circular dish has a radius of exactly twice the focal distance (r=2f; see my earlier post). This can be used to get an idea where the LNBs should be located, given the following notions:

Seen horizontally, ALL signals from satellites that go through the center of this circular form (so the point at distance 2f from the dish), come back from the dish in the direction of the circle center again (due to the 90 degrees, as mentioned above). Halfway between dish and circle center is the focal point for that satellite.

So if the satellites have an angledifference of x degrees in the horizontal plane (usually people use the azimuth-difference here, which has a similar value, though that is not the correct measurement I believe), the angledifference of the LNBs seen from the centerpoint of the circular form should also be x degrees.


Hope I explained this for everybody's understanding.....

greetz,
A33
 
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rayhan

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My Satellite Setup
DIY toroidal
My Location
Vadodara, India
Thanks a lot guys. I guess I've understood the geometry of the dish pretty well now.
To quickly skew the dish, I drilled slots in the dish only (refer pics). I was able to capture the central satellite (Insat4A 83E) and one other satellite (GSAT15). However, I wasn't able to capture ABS2 (the satellite with weaker signal).

Now I'm working on a proper mount to skew the dish, very much similar to the wavefrontier T55. Also, I'm changing the mounts. Again similar to the T55. I hope after I get all the new clamps made, I would be able to capture ABS2 as well.

I have a question though. The satlex calculator is meant for Wavefrontier. I guess the focal length of my dish would be different from that of wavefrontier. So in essence, the skewing angles for my dish should be different than the ones that I get from Satlex. Is there a way that I could calculate the skewing angle for my dish? The only satellites I'm interested in are :
1. ABS2 (74.9E) - Azimuth 175 and elevation 63
2. GSAT15 (93.5E) - Azimuth 135 and elevation 55

The middle satellite for my setup would be Insat 4A 83E.
The focal length of the parabola and the half of the radius of the circle is 360 for my dish. The total length and width of the dish are 1000*570 mm.
 

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RimaNTSS

RimaNTSS

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Some SAT-related hardware.
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The satlex calculator is meant for Wavefrontier. I guess the focal length of my dish would be different from that of wavefrontier. So in essence, the skewing angles for my dish should be different than the ones that I get from Satlex. Is there a way that I could calculate the skewing angle for my dish?
Satlex calculator will give you proper skewing angle. It will not calculate proper distances between LNBs.
 
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a33

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Satlex calculator will give you proper skewing angle.
(That is because dish skewing angle is only dependant on angle between satellites for your location, so NOT dependant on dish size or focal distance or whatever.
Dish skew is normally calculated for the two 'widest' locations on the multifeedbracket.)

Greetz,
A33
 
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archive10

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Thanks a lot guys. I guess I've understood the geometry of the dish pretty well now.
To quickly skew the dish, I drilled slots in the dish only (refer pics). I was able to capture the central satellite (Insat4A 83E) and one other satellite (GSAT15). However, I wasn't able to capture ABS2 (the satellite with weaker signal).
Well done, sir!

Firstly: Full Kudos to any one who make their own reflector from scratch.
I cannot overstate this - I am really impressed with your project.
Most people buy their reflectors. Very few make them from scractch!

And now to take in the skewing advice in the mount - just shows the can-do-attiude you have.

Wrsp to skewing, @RimaNTSS and @a33 are right - it's not specific to the WaveFrontier, but will work on your dish as well.

Keep going, you'll be there soon!
 
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Oh, dear masters of the univ... I mean, of this website.
Could we not spin Rayhan's story off from this thread, as it is not really about the SMW OA-1600, but does rather deserve it's own special thread in the "Pictures of member's dishes"?
 
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Oh, dear masters of the univ... I mean, of this website.
Could we not spin Rayhan's story off from this thread, as it is not really about the SMW OA-1600, but does rather deserve it's own special thread in the "Pictures of member's dishes"?
Go for it. we always like photos ;-)
 
RimaNTSS

RimaNTSS

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As I've deinstalled and sold my SMW-OA-1600 I've started renovation and upgrade process of the second one. I will fix it on the same place where first one was . Will install 8 Quad LNBs on it. And this antenna will be manly for watching TV- 3 feeds in living room and 1 feed to the garage.
Digged out back frame. It will need some paint. Then shortened 2 original feedarms and made new setup for LNBs. Of course INOX :)
My standard LNB-holders will be used.
 

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As I've deinstalled and sold my SMW-OA-1600 I've started renovation and upgrade process of the second one. I will fix it on the same place where first one was . Will install 8 Quad LNBs on it. And this antenna will be manly for watching TV- 3 feeds in living room and 1 feed to the garage.
Mine's never made it out from behind the out-house.
I am hoping that I might get it up and running during the summer.
At least SWMBO has recently stated "all the dishes needs to be used, or they've got to go".
So I suppose I've better get it up. (The dish, that is...)
 
Channel Hopper

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A keeper for sure, make sure it's only your erection she has an interest in.

 
RimaNTSS

RimaNTSS

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From 35x35x2mm tube made part of the back frame for antenna. At lest I know that this part will not need to be painted and will not rust.
 

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RimaNTSS

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Metal-brushed all the rust and painted the frame in my favorite color. Still need to make elevation mechanism. Hope to install this beast ASAP, other-ways my neighbour can not watch many TV channels he likes.
 

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Metal-brushed all the rust and painted the frame in my favorite color. Still need to make elevation mechanism. Hope to install this beast ASAP, other-ways my neighbour can not watch many TV channels he likes.
Did you buy a whole barrel of that colour??
Seriously, it does look good. Much bette than my rusty old original mount.
But it will probably work. Once I get time to put up the dish...

What do you do to the metal first? Wirebrush, then sandpaper?
 
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