reclaimed Unimesh 7.5' and LNBF question

[talkdty]

hi guys,
with a 7.5' dish
and 14.125" depth
I'm coming up with a focal point of 35.84"

Now with the four supporting legs attached to the WSI C/Ku LNBF (part # 741) do I simply slide the LNB between the markings for "36" and the line (going lower & closer) next to it ...?

what I'm trying to get my head around is this : different mfr dishes may have different support legs length, so would the LNBs placement on my 7.5' be the same on my neighbor's 7.5' but a
different brand... ?

I'm not sure if my question is conveying what I'm curious about, so I'll try it another way: Two different mfr dishes may have the same diam. and the same dish depth; so in my mind they SHOULD have the same focal point, but if I swap out the OEM scalar ring and LNBF to a replacement WSI 741 (and scalar ring) and bolt it onto the old dish's four support braces... how did the LNBF mfr know that the markings on his product match my calculated focal point of 35.84 inches ???

second quandary: Is the focal point supposed to converge right at the LNBF's front weather cap, or inside a inch or two past the cap and down the LNBF tube ?

 

[FaT Air]

would the LNBs placement on my 7.5' be the same on my neighbor's 7.5' but a
different brand... ?

Maybe, but only if the F/D ratio is the same.
F(35.84) / D(90) = 0.3982 F/D=.4 Set scalar on feed throat so .4 mark aligns with the backside of the scalar. Mount scalar to legs so front edge of feed throat is ~1/8-1/4 inch short of 35.84. (35.5??)
Fine tune feed performance by sliding the feed in/out of scalar. Should only be slight.
Dual band LNBF's require diligent fine tuning. You also may see one band peaks here, and the other -there. There's a 'trade off' in performance to accommodate both bands.

 

[talkdty]

that clears it up a bit,
so the side markings on the LNBF is only for its accompanying scalar ring then, and its up to the end user to present the assy to his/her particular dish's focus point........ now I think I'm getting clear on this...

 

[FaT Air]

Scalar rings are set to the F/D* ratio. Then the feed is fine tuned.
*Focal length/ dish Diameter. The small 'fine tune' adjustments are usually small and don't effect the F/D ratio enough to worry much about.

Make sure the feed is centered. Measure 3 points around the dish, scalar edge to dish edge.
Also ensure the feed is aimed at the bottom center of the dish.
These two areas can really effect perforance

 

[T4Runner]

That's why those slotted strut ends are so important. This adjustment is the one that took so long on one of my 7.5ft dishes. Getting the distances equal so the scalar was parallel to the dish. Then tweaking the LNBF for what seemed forever...


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[talkdty]

wow, that is the prettiest donut hole I have ever seen, you got the baby lined up PERFECT !!!

 

[T4Runner]

wow, that is the prettiest donut hole I have ever seen, you got the baby lined up PERFECT !!!

Yes, but took forever... I did the same thing you are trying to do and but also replaced the struts with 1/2" EMT and made them match the original lengths and angles.

My depth was 14 1/2" on both my 7.5 ft mesh dishes.




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[talkdty]

do you by any chance remember the measurement from the bottom of the dish "bowl" to the LBNF's weather cap after your final peak ?? basically the photo above, but AFTER the LNBF is in place....?

 

[T4Runner]

do you by any chance remember the measurement from the bottom of the dish "bowl" to the LBNF's weather cap after your final peak ?? basically the photo above, but AFTER the LNBF is in place....?

No, and I cannot measure it now because its up too high, but the PEFECT 10 manual on this website has exact measurements for the 7.5 ft mesh to be 33 1/4" from the flat base plate in the center of the dish to the LNBF.



I was told by members here to follow the manual exactly when installing my 10 ft and I did and it is perfect.


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[talkdty]

thank you, this has been [Viewsat] EXTREEM-LY helpful

thanks again:up