Difference between C band LNBF and C band offset LNBF

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adrian

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Jan 23, 2006
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How do one ascertain the difference if an offset is available.?On a KU offset dish what is the best way to determine the focal point of a C band LNBF.Thanks for any assistance.
 

AntAltMike

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Aug 28, 2005
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The focal point is the same for Ku or C. With prime focus dishes, the F/D ratio is typically .30 to .45. With offset dishes, the F/D ratio is typically around .6. The feedhorn is optimized to match the F/D ratio of the dish. If you use a feedhorn optimized for an offset dish, like a DBS LNBF, for a prime focus dish, the LNB waveguide will reject signal coming from the perimeter region of the dish, whereas if you use a prime focus styled LNBF for an offset dish, the feedhorn will "see" a little more off-boresignt noise and develop a slightly inferior signal to noise ratio.
 

adrian

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Jan 23, 2006
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Thanks Antaltmike.I am using a Prodelin 1.2M VSAT offset dish with a F/D of .8
I am receiving KU pictures using a .3db feed.The problem comes when i try to receive C band feeds using 20 degree C band LNBF.The signal is there but i dont seem to lock in.Are C band offset LNBF,s available?
 
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AntAltMike

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Aug 28, 2005
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Thanks Antaltmike.I am using a Prodelin 1.2M VSAT offset dish with a F/D of .8
I am receiving KU pictures using a .3db feed.The problem comes when i try to receive C band feeds using 20 degree C band LNBF.The signal is there but i dont seem to lock in.Are C band offset LNBF,s available?
EVen if there are, I doubt that you would gain as much as 1dB of S/N ratio. The problem you face is, your dish is too small for reliable C-band reception under nearly all real world circumstances.
 

HDTVFanAtic

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May 23, 2005
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Thanks Antaltmike.I am using a Prodelin 1.2M VSAT offset dish with a F/D of .8
I am receiving KU pictures using a .3db feed.The problem comes when i try to receive C band feeds using 20 degree C band LNBF.The signal is there but i dont seem to lock in.Are C band offset LNBF,s available?

First, the Prodelin 1.2 VSAT has some serious C Band issues with that model - regardless of the fact it will probably never work.

Second, you need new spars for it and Prodelin sells them for about $180 on that model. I know - I looked into it.

FWIW, now I am thinking that the offset issue was why my Invacom Quad did not work well in that setup while the Dish lnb minus the plastic casing blew it away - even though it was the Prodelin assembly attached to the Invacom.
 

truckracer

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Sep 17, 2004
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Charleston wv
I had a prodelin 1.8M offset for about a year using a c band lnbf and it performed great on g10r.

I got strong signals but i had to make my own mount out of hardware store slotted steel for my lnbf since this thing had a hughes network radio and feedhorn on it when i got it.

I took it down and intalled my motorized sami mesh dish.
 
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