Focus on LNB

[Rizwan]

Please clear this for me, Where beam should focus on LNB ? at the openning, where scalar ring are OR inside at its sensors ?

[Detlef]

It depends on the LNB. The only way to get a spot on focus is to connect it all up with a meter and then try sliding it backwards and forwards in its clamp for maximum signal.

With C120 set-ups it must be just inside the feedhorn as you can add polarisers, skew elements and a bodge to turn circular to linear adapters between the feedhorn and the LNB aerial stubs and they don't change the focus.

Sly dishes mostly have a fixed location for fore/aft though.

[Mumbles]

My Invacom work better without the scaler ring on. As detlef say above. The signal kinda bounces up the feedhorn and yo adjust to find the best result.


My Invacom scaler ring thingy - as you are probably now wonderiing about - is now attached to my lawnmower and being used to lower the blade.

[Barney]

Inverto Black Pro C120 LNB on my Prime Focus 2 Meter dish .
im certain someone here advised me quite a long time ago to quit wasting my time with Scaler rings on C120 LNB as signal decreases ..i made a few tests to try prove him wrong long time ago ..but im afraid he was right lost around 14% with Scaler rings regardless of how much i adjusted now i just use LNB without scaler rings as ive found out the most critical thing is just getting the skew on LNB Right on as i totally do believe Big dishes really dont need much effort to beat a smaller dish since signals on a big dish will always maintain that constant signal that smaller dishes always will loose on poor weather conditions .
But very interesting point by Detlef regarding C Band i never really tried C band simply because i dont think there is a lot of C Band channels to be got nowadays but someday i will give it a shot to see if its worth it or not : )

Good luck .
-
Barney

[Rizwan]

I have slightly Big Dish about 3.5 Meter prime focus and only try weakest satellites. I found scalar ring is excellent on some frequencies and worst with other on same satellite

[Rizwan]

If this clear to me, then I change my LNB or Feed horn to get much Signal with adjusting

[Rizwan]

I am looking for the Answer for my Question, Where the Focus required on LNB ?

[unimesh7Fowner]

the scalar rings are for C band LNB but not required for Ku band LNB. therefor you only need the Scalar rings for a C Band or a combined C /Ku band . In fact it will reduce the performance of a Ku band . If you remove the rings for a Ku band then you will slightly get better signal. Normally there are scales on the cylinder of a C or C/ Ku band lnb marked 0.2 to around 0.8 . You set this to the F/D ratio of the dish.

Where to focus the beam ? This again depends on the LNb . this information can be got from the manufacturer. Otherwise just take detlef advice ie do it by trial and error( Move in or out).

[stars]

I would say that the feed horn should be at the focal point of the dish and the scalar rings
or feed horn (KU-Band) must be adjusted to the right F/D ratio of the dish. :)

stars

[Detlef]

the scalar rings are for C band LNB but not required for Ku band LNB. . . . . . . . . ).

Sky LNBs have elliptic scalar rings to match to the elliptic Zone 1 or 2 dishes - you need to pop off the plastic weather shield to see them.

[Rizwan]

If Scalar ring with C-band , then why Invacom LNB with C-120 have Scalar Ring ?

[ABA]

the focal point of any lnb is the centre of the feed horn about 1/8 of an inch in
dont matter what the lnb is,
dont matter if the lnb and feed horn are two seperate units bolted together
or just one unit

[Detlef]

I'm sure that is true where the feedhorn is a virtual waveguide (ie. parallel sided orifice) but I have my doubts when it is a funnel shape as on most uni-LNBs.

[Rizwan]

Many members thinking, what type of discussion I start, As I say earlier, I have big Dish, so it reflects more signals, I am afraid that Its feed is not on proper position and I am missing some weakest frequencies, So I am looking for some advice and also about Feed Horns

[cosworth4x4]

ive sent you a pm that web page cannot explain it any better.

[stars]

the focal point of any lnb is the centre of the feed horn about 1/8 of an inch in
dont matter what the lnb is,
dont matter if the lnb and feed horn are two seperate units bolted together
or just one unit

What I mean is the focal point of the satellite dish. Here is the signal at it's maximum.
If you are to deep or far out from this point you will loose signal strenght.

The scalar rings are different depending on which type of satellite dish you are using.
For Offset dishes they are cone shaped and for Prime focus dishes they are circular.

This is due to the shape off the satellite dish. Every LNB have got a feed horn so the
signal can efficiently guided into the LNB "wave guide tunnel"

The antenna rods on a big C-Band dish is often bolted to the feed horn for the C-band LNB.

stars :)

[Rizwan]

ive sent you a pm that web page cannot explain it any better.

Sorry dear, there is not much help on that page



What I mean is the focal point of the satellite dish. Here is the signal at it's maximum.
If you are to deep or far out from this point you will loose signal strenght.

The scalar rings are different depending on which type of satellite dish you are using.
For Offset dishes they are cone shaped and for Prime focus dishes they are circular.

This is due to the shape off the satellite dish. Every LNB have got a feed horn so the
signal can efficiently guided into the LNB "wave guide tunnel"

The antenna rods on a big C-Band dish is often bolted to the feed horn for the C-band LNB.

stars :)

Your all points are valid, In my issue I am only concentrating on KU-band LNB, 2nd, I just want to know, Can I use LNBF, like Inverto ultra Black on my Prime focus Dish ?

[cosworth4x4]

[QUOTE=Rizwan;885129]Sorry dear, there is not much help on that page




:eek:

[cosworth4x4]

[B]Your all points are valid, In my issue I am only concentrating on KU-band LNB, 2nd, I just want to know, Can I use LNBF, like Inverto ultra Black on my Prime focus Dish ?


yes of course you can, and that website would have shown you how to calculate the focal point were you will start off with and fine tune after , what has already been said above.

[stars]

Yes, you can use it. But since the feed horn is optimised for an offset dish
and the f/D ratio is high maybe between 0,45 - 0,60 you wont be able to
use the whole dish size area. And there for you can't get the maximum signal strength
that the dish can give you. 58500

But if you have a C120 LNB and a feed horn for prime focus dish you can use the dish
to its maximum. Invacom have a feed horn that fits and you can adjust it for the right
f/d ratio. It's called ADF-120

If you are hunting weak KU-Band signals and have a mesh dish the efficiency of the dish
will be poorer than a solid dish. The efficiency of a Prime Focus dish is about 57 % and an offset
dish is about 65-70 %. So a PF 1.8m dish is almost the same as a 1.5m Offset dish.




stars :)

[satwyn]

Sorry dear, there is not much help on that page




Your all points are valid, In my issue I am only concentrating on KU-band LNB, 2nd, I just want to know, Can I use LNBF, like Inverto ultra Black on my Prime focus Dish ?yes if they come in c120 to bolt onto a feed but you could also use a lnbf on your dish if you can mount if properly to the dish

[Rizwan]

Now later I try to attach a pic of my LNB and also feed I am trying

[cosworth4x4]

as previous pics , i really dont think you can get fred in the shed to make you a feedhorn to be any good.

you was advised to try and get a invacom universal( if i recall) then bolt up youre black ultra.

i dont think you are going to get a matched feedhorn for that dish so you are going to have to make good with whats available.

then work out (from the site i sent you) the focal point , and that will be the same if you use a feedhorn or just bolt up the lnbf.

then fine tune from there.

[stars]

I have done some calculations

Dish size: 350 cm
Dish depth: 53 cm
Focal point of dish: 144.45 cm
F/D ratio: 0.41

The Invacom ADF-120 will manage up to F/D 0.43

I hope my calculations are correct...

stars :)

[Rizwan]

@stars

I have 3.5 meter Solid Dish not a Mesh and its Prime focus, but Unfortunately I am unable to find the Prime focus feed in my local market

[Rizwan]

Here I attach some pictures of feed horn I use with my LNB, Currently I am using Inverto Ultra Black

58660586615866258663