Advice Needed Inverto black ultra feedhorn .. F/d ??

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mirrors

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#1
Hi guys
I want to ask about how much the accurate F/d of antenna dish that suits an Inverto Black Ultra LNBF feedhorn ???
Is it 0.65 or 0.6 ??
If there is any E-link to datasheet .pdf will appreciate it ...
Thanx
 

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Channel Hopper

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#3
I've cut the feed off a few LNBFs in the past year and all look roughly the same in terms of feed angle, number of scalar rings and casting marks. The only changes that are plainly visible are the throat diameter (the Invertos use a smaller measurement, presumably to enhance the upper band) and the depth of the throat itself, which is in the main to allow a better - read more universal - focal point adjustment to multiple reflectors.

I do not know of many domestic offset dish designs that stray from a focal distance f/d ratio of 0.65-0.7 meaning an illumination of approximately 70 degrees at centre point. For professional dishes however this is too wide, the maximum on a Prodelin dish is 51 degrees (0.6 f/d), with 39 degrees (or f/d 0.8) being the Ku standard for certified transmission characteristics, preventing trouble with adjacent satellites.
 
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antrabe

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#4
which lnb is advised to use in ku band for prime focus
 
Channel Hopper

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#5
Something that will bolt onto the feed that is designed to work with such a dish.
 
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a33

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#6
Found this on the internet
Well, if this LNB is designed for offset dishes and the f/D of 0.6 mentioned in these specs is the f/D of an offset dish, then the D will be the width of the offset dish, but the f will probably be the f of the mother Prime Focus dish!

In that case the value for a Prime focus dish with f/D=0.6 for the feed subtended angle (namely: 90 degrees) will not apply; the LNB viewing angle for an offset dish will probably be around 70 degrees as @Channel Hopper wrote.
For 70 degrees feed subtended angle, the 'f/D ratio equivalent' (as for prime focus dish) would be about 0.79. So that feedhorn (with f/D=0.6) would fit to a PFdish with f/D=0.79.

This confusing terminology of f/D with offset dishes was already mentioned here (but without solution): Feedhorn Illumination Angle - SatsUK

Though I found that topic just today, I was concerned with this issue also recently.
I guess for certain signal quality calculations of offset dishes, the f/D with 'f=prime-focus-focal-distance' might be of importance; but I don't know much about that.
For dish geometrics and LNB viewing angle of offset dishes, the "f/D-ratio-equivalent" is more meaningful, I think. Formula and a calculator you can find here: Calculator voor LNB-kijkhoek en f/D-ratio-equivalent voor offset schotels


@mirrors : Is it the LNB-viewing angle of the LNB you want (angle of dish subtended by the feedhorn), or something else?

Greetz,
A33
 
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mirrors

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#7
@ A33
Thank You so much for that detailed rich reply .
let me simplify what I asked about ..
There are 2 prime focus antenna dish had been offered to me . both with 180 cm diameter
the first one with 17.5 cm depth .. which make its F/d is 0.63
the second one come with 18.7 cm .. which make its F/d is 0.6
so I asked as above ..
now .. which one will be better to use with Inverto Black Ultra ??
and , how much is the (angle of dish subtended by the feedhorn) for Inverto Black Ultra ??
 
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a33

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#8
the 17.5 depth dish has LNB viewing angle 85 degrees (focal distance 115.7);
the 18.7 depth dish has LNB viewing angle 90 degrees (focal distance 108.3).

So assuming the black ultra has a viewing angle of about 70 degrees (for "standard" offset dishes), you'd use more dish surface of the 17.5 depth dish than of the other one.
(I'm assuming the angles should ideally match 1:1 ? I am no expert on LNB feedhorns I'm afraid. So I'm open to feedback of other forum members on this point.)

An LNB with adjustable feedhorn is not an option for you? Because with a 70 degree feedhorn you'd only effectively use a diameter of about 150cm of your 180cm dish I guess, though with less spillover losses than with a real 150cm dish.

greetz,
A33
 
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RimaNTSS

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#9
There are 2 prime focus antenna dish had been offered to me . both with 180 cm diameter
the first one with 17.5 cm depth .. which make its F/d is 0.63
the second one come with 18.7 cm .. which make its F/d is 0.6
Chose dish which is less warped. IBU is designed for an offset dish, so it is not so correct to use it on PFA. Of course, it is possible to attach proper feedhorn to IBU, but better is just use LNB which is designed for PFA, for example GI-209P.
 
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#10
@ A33
Thank You so much for that detailed rich reply .
let me simplify what I asked about ..
There are 2 prime focus antenna dish had been offered to me . both with 180 cm diameter
the first one with 17.5 cm depth .. which make its F/d is 0.63
the second one come with 18.7 cm .. which make its F/d is 0.6
so I asked as above ..
now .. which one will be better to use with Inverto Black Ultra ??
and , how much is the (angle of dish subtended by the feedhorn) for Inverto Black Ultra ??

Buy a feed that can be adjusted to the correct illumination of the reflector, if a dedicated one does not come with the one you decide on.

Bear in mind it is almost certain you will have to fabricate your own feed arms and clamping system and getting the correct distance could mean some metal left over.
 
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mirrors

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#11
@ channel hopper
@ A33
@ Rima NTSS
I'm so grateful for your replies , now I can imagine what is the way LNB related to antenna dish
but , new Qeustions jump into my head :confused
1- Is there any Prime focus Antenna with F/d = 0.79 or 0.8 ?? "which is sooo shallow"
2- If there is such antenna , would it works perfectly with offset dish LNBF such as Inverto Black Ultra ??
 
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#12
No and no.

But why not build one to find out ?
Post results here.
 
RimaNTSS

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#13
In theory, if there were shallow PFA with opening angle ~80* then IBU would work OK. But I did not see such a dishes (that does not mean they do not exist).
For me is much more simple to use terms "opening angle" for antenna and "illumination angle" when we speak about LNB. And it is best when those 2 angles match each other. Moreover, in offset antenna case, as already mentioned by @a33, F/D does not really make cense unless we speak about some kind of "F/D equivalent"
 
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mirrors

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#15
In theory, if there were shallow PFA with opening angle ~80* then IBU would work OK. But I did not see such a dishes (that does not mean they do not exist).
For me is much more simple to use terms "opening angle" for antenna and "illumination angle" when we speak about LNB. And it is best when those 2 angles match each other. Moreover, in offset antenna case, as already mentioned by @a33, F/D does not really make cense unless we speak about some kind of "F/D equivalent"
yes it is obvious to me now about the offset dish tricky (F/d) which is said to be 0.6 (referd to the mother dish) but it is actually = 0.79 .
As A33 explained .
I remember 1 point to ask about . I can explaine it by photo .
sorry if I'm asking too much .. :rolleyes:
 

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#17
Look here, do not worry about language just scroll down till you see pictures and animations.
I remember one time we (members of this forum) wrote to producers of IBU asking about location of phase center and answer was: it is ~5mm behind the white cover.
Added later: OK, that was ~4 years ago when answer from IBU received. We had discussions about it here
 

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mirrors

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#18
Look here, do not worry about language just scroll down till you see pictures and animations.
I remember one time we (members of this forum) wrote to producers of IBU asking about location of phase center and answer was: it is ~5mm behind the white cover.
Added later: OK, that was ~4 years ago when answer from IBU received. We had discussions about it here
great reply RimaNTSS !!:-clap:-clap
that is what I originally asked about
F/d and the Illuminate angle of IBU :-clap:-clap
so it's 0.6 & 84'
 
TonyilCapo

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#19
Hi @mirrors
Depending on what you want to set up, you might find that an (offset) LNBF will give you enough signal for your PF dish setup.
You will always lose signal doing something like that, but it may be worth it.

I have a 2.4m prime focus dish with a Octagon Quad Optima mainly to get the UK beams from 28.2E and signal is good enough.
Even with heavy rain is not so bad
In my personal case to get a proper LNB 4 outputs + feedhorn is very difficult locally, and the ones I find cost more than I gave for that 2.4m used dish.
I had modified the LNB mount to hold the LNB farther away from dish (+-1cm), this gave me almost 2dB gain.
 
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mirrors

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#20
Hi TonyilCapo
thank you so much for passing by and sharing what do you know ..
I just wonder how much the depth of your 2.4 m antenna ??
I think you cut 2 rings of the LNBF feedhorn and add a flat flange feedhorn instead if your dish with F/d = 0.38
 
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