Single feedhorn or dual feedhorn?

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belter-one
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Single feedhorn or dual feedhorn?

Post by belter-one » Sat Nov 03, 2018 3:21 pm

Hello,

We are enjoying our C band system immensley. The current LNB position on the dish is barely able to tune all the channels we are interested in.
I adjusted the LNB position in the feed horn and peaked the SNR on Galaxy 13 (NASA 3920V) and Galaxy 14, to SNR of 14.9 - 15.2 on NASA, and
14.7 on a C band transponder on Galaxy 14. This was what I considered awesome for C band, and the C band channels we were interested in
tuned very nicely with the LNB setting. However the Ku channels on Galaxy 14 dropped to 0 SNR. I re-adjusted the LNB, and found a setting
where we are able to get both the C band channels (some just barely), and the Ku channels. The NASA 3920 transponder is down to 13.6 SNR,
and the Galaxy 14 transponder went down from 14.7 to 11.4. If the single LNB feedhorn was swapped out with a dual LNB feedhorn, would this
allow both C and Ku LNBs to increase their SNR? Would the C band LNB occupy the prime focus, or would neither of the LNBs occupy the prime
focus position? Any help on this would be appreciated, as I am unsure on how to best proceed.

Cheers and have a great day,

belter-one.

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Re: Single feedhorn or dual feedhorn?

Post by fatso » Sat Nov 03, 2018 11:38 pm

Best way to peak both C band and Ku band is to get them to ride 'shotgun'. Start by peaking your C band LNBF on a single prime focus scalar ring. Once you got that peaked, add a ku band prime focus LNBF right beside it and get that peaked. You'll have to find a way to attach it. Some people cut the scalar ring while others position it further out so no cutting is necessary.

You need something like this for prime focus ku reception:

http://www.tek2000.com/cgi-bin/web.cgi? ... %20LNBF-ND


It does work, but you got to get the ku LNBF in the right spot to track the arc. I think there was a tutorial on this topic some place...section 8.5

https://www.tvrosat.com/forum/phpBB3/vi ... 1258e2efdd
12ft Mesh Dish
C-Band Enthusiast since 1983

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Re: Single feedhorn or dual feedhorn?

Post by belter-one » Mon Nov 05, 2018 12:45 pm

Thank you for the reply,

The tutorial was very informative. Since my dish is a 10 footer and not a 12 footer, I believe I cannot ride shotgun next to the C LNB with the Ku prime focus LNB, as a 12 footer minimum is needed to allow for the LNB to pick up the signal 2 inches from the C LNB. So, I believe 4 inches away would be possible, according to the tutorial. Sounds like its time to get the ladder out and have at it.

Cheers,

belter-one

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Re: Single feedhorn or dual feedhorn?

Post by tvroadmin » Tue Nov 06, 2018 1:06 am

Some good reading here:

http://www.afcsat.com/dual.html

Unfortunately, such a commercial solution will likely set you back several thousand dollars, assuming you can find a company that make such a product.

Your best bet is to construct your own "yuri" feed:

https://www.satelliteguys.us/xen/thread ... lnb.92536/

Just get yourself a scalar ring and cut out a 1" canal where you can insert the ku LNBF. I've done this on a 10' dish and it works extremely well. Your sats will be spaced apart by 4 degrees. For example, if your C-band LNBF is aimed at 121W, then your ku LNBF will be aimed at 125W or 116.8W, depending on which side you mount it on. If you do this on a 12' dish, then the satellite spacing would be around 2 degrees.
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