# how do figure out how far to space multiple LNBFs

Discussion in 'Free To Air (FTA) Discussion' started by jholt5638, Sep 1, 2017.

1. #1
I'm happy with the amount of programming I get with my slimline but not trilled with having to move the dish back and forth.
I figure I have three options

1. multiple dishes
2. motorize the dish
3. multiple LNBs

Of those, three is the least expensive of the options. So I bought two more Avenger KSC 321S-2, a multiple LNB mount, and a Pansat 4X1 with the weather cover all from hypermegasat
Now once they arrive, how do figure out how far to space them I am trying for 103W 97W 91W or 103W 97W 87W. I'm sure there is math that makes easier than guessing

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3. #2
Well once you get it about where you think it should be, you will end up tweaking the whole arrangement anyway. The math is complicated. You can figure that two Bullet LNBFs (40mm)side by side will be approx 4°~5° apart on that dish.

4. #3
You would need to know precisely what the surface of the dish looks like to be able to do any math. Because the Slimline is a custom-engineered dish, I would assume that it is not regular (geometrically symmetric) parabola like you would get with a conventional FTA dish.

For their part, DISH discovered that the 1000.4 dish couldn't readily be adapted to Western Arc use by using a different LNB assembly and ultimately forbid installers to deploy them.

5. #4
Well, here's a topic about it: Multifeed installation and exact calculation of LNB position

I know now, that theoretically not difference in Azimuth is needed, but difference in Hour Angle. (though that doesn't make a big difference.)

As for the diminishing factor mentioned in post #13: I'm not sure about the reason for that. Also he didn't calculate with Hour angle, but with Azimuth, if I recall correctly.
I read somewhere else about a diminishing factor out of theory, but it's too mathematical and complicated for me to comprehend that till now.
For now, I wouldn't really calculate with a diminishing factor. But I haven't checked distances in practice...

BTW: Effective focal distance of an offset dish is the distance from focal point of the dish (where the phase center of the LNB hopefully would be) to the G-spot of the dish (this name is introduced, I believe, by RimaNTSS?).

When you have a straight multifeedrail (not following the mirrored curve of the clarke-belt), the rail/dish tilt is important. That can be calculated for the two chosen outer satellites and your location, and is undependant of dish size or dish characteristics!
Finding the satellites is much easier, when you already have set the right tilt: you just have to shove the LNB along the rail (so adjusting only ONE dimension..).

The fact that the slimline dish is not 'normal' (not higher than wide), is not very important I believe. Vertically it will still be parabolical; horizontally it might be the circular (as in "spherical") or mixed circular and parabolical. The horizontal LNB distances will be quite near the distances for a purely paraboloid dish.

Greetz,
A33

RimaNTSS likes this.
6. #5
You are going to have to use A LOT of patience and perseverance. This is where a good satellite meter would come in very handy.

iBoston likes this.
7. #6
So what I'm hearing is carry my tv and receiver out to the dish mount all the LNBs, figure out the tilt of the bar so all three will at correct angle, aim the center LNB at 97W, move the other two slowly till each one is locked in basically

8. #7
Jholt you can do that. but it is easier with a round dish just remeber follow the curve of the satellite arc.

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9. #8
About a year ago, i bought a DVBs2 satellite digital meter. That makes life MUCH easier. It is what i used to find signals and fine tune. Just start with the strongest signal on the satellite.

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10. #9
Thanks everyone I think I got it figured out enough to get lucky for the 103 97 91

the three LNBs should be almost touching each other since they are roughly 5 degrees apart.
The difference in height between 91 and 103 is 3.4 degrees so tilt whole dish by that so it follows the arc
Set the correct skew on all LNBs
Aim center LNB at 97 and that should be in the ballpark

sunelec and kittyhas1000legs like this.
11. #10
Don't forget you can skew the entire dish to follow the arc or skew the LNBs individually. Also at best the entire setup will be a compromise. The slimline is really better suited for the high power pay per view sats rather than the FTA market. Each LNBs will only see a small segment of the dish. You may be disappointed with the results especially with 103W.

12. #11
Yeah 103W doesn't really like the slimline I can pull in 11760, 11942, 12145, 12180 right now. In the multi lnb setup I'll be happy with getting 11760 and 11942

If this experiment works out I think my ultimate plan is to have a

two 3ft ku-band with multiple LNB's each
one for 103, 97, 91.
The second for 99, 95, 87

and finally lock the slimline down on 121 for Velocity

jorgek and KE4EST like this.
13. #12
No.
Dish/multirail tilt should be about 11.21 degree (with the 103W LNB as the highest); see the calculated outcome of SatLex Digital :: Technology :: Calculators :: WF Toroidal Calculator

BTW: To skew the entire dish is better than to just skew the multifeedrail!
BTW2: If 103W is the most problematic, you could also put that LNB in the centre. If 91W is strong, I would first try that for set-up?

Greetz,
A33

kodaz and jholt5638 like this.
14. #13
That's a tough one, because 103W is hard to get (if you want the NBC muxes), and 87W is also hard if you want the LBC mux.

So maybe do this:
Dish 1: center on 103W, side LNB on 99W and 95W (99 and 95 are easy)
Dish 2: Center on 87W, side LNB s on 91W and 97W

you could swap the 99, 95 LNB set with the 97 LNB between the 2 dishes and see what works best. 97 can be a bit touchy sometimes

15. #14
1. multiple dishes...... good if the dishes are free or near it
2. motorize the dish.... best idea. 1 meter or more..... be happy
3. multiple LNBs .... on a slimline.... good luck

16. #15
I was told the same thing when I first started talking about using the slimline at all. Not here but other forums and groups. Told I'll be lucky to get anything at all.

Now I admit I don't everything ku has to offer notably 125W and all the NBC muxes on 103W. I just get the COZI/West/Mountain along with 11942, 12145 and the feeds when they pop up. Between those, 87 with the LBC mux the 150+ channels on 97, and the others on 95, 93, and, 91 I haven't had problem finding something to watch.

If the multiple LNB's doesn't work, just about every house on my block has a unused DTv slimline/Dish 1000/Hughesnet dish on it. I'll start knocking on doors I'm sure I can get two more dishes just by asking.

Even with the equipment I just bought I've spent less than the cost of one month of cable television. Ultimately this is a learning experience and I figure if I can do it using a undersized dish it will make setting up a actual ku/c dish it will be breeze.

17. #16
there's a lot that you can get with small dishes. Even a Dish500 will easily get the NHK mux on 103, and the CCTV mux on 95 W and many more. I'm currently using a slimline on 30W and get most channels - just a bit tough for T5 Satelital. I'm quite impressed that you get LBC on the Slimline though. Congrats!

However you'll probably notice that during heavy rain, that will be a bit of a different story. In my experience, the NHK mux on 103 is maybe the most resilient, but most channels might get unwatchable during heavy rain.

BTW, KBS World on 123W is another channel that's quite good (many shows are subtitled in English) and is easy to get on a small dish.

18. #17
Stuff should arrive today, I did manage to get another slimline yesterday considering mounting under the first dish and have it fixed on 121 no need to change out the LNB for that and maybe later on pick another LNB and move it to 123

19. #18
You put "or" , I would say "and" , I mean "multiple dishes, motorize dishes and multiple LNBs"
TBH, I do not like multifeeds unless they are made and installed on multi-focus dishes like T90 or others.
Of course I know how to install multifeeds on simple offset dishes, as I did it several times. I also did think a lot about best technical way for making multifeeds.... some kind of universal ones. After lots of trials I came to the one of the best (IMHO) solutions to build multifeeds. Universal means, this multifeed can be installed on almost any satellite antenna and, depending on the clamp used, can hold Ka/Ku/C-band LNB. On the following picture I have used piece of wood to represent the feedarm. Of course. central LNB should be installed in the focus of the dish, but multifeeded LNBs are located at the position were maximum signal level is received. I like when antenna is skewed, not multifeed, then antenna-system is performing better.
Same LNB-holders can be used to create bigger multifeeds on multi-focus antennas. Those sets I am making for couple of friends of mine for their T90s
For tight multifeeds it is better to use LNBs with small feedhorrns.