Ku on big dish?

mr3p

mr3p

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My HH motor recently failed and while I have a replacement, just wondering about possibility of adding a Ku LNB to my 10ft KTI dish? Long ago I tried a combo C/Ku LNB and wasn't happy with the Ku performance but just wondering if a separate Ku LNB added next to the scalar might be sufficient?
 
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primestar31

primestar31

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Do you know about how many degrees away from center will a sidecar ku LNBF be facing if just outside the C band scalar?
Likely 8 degrees minimum. Make sure it's mounted in a straight line with the center of the scalar, otherwise it'll be looking either ABOVE or BELOW the satellite arc.
 
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c-spand

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It varies. I just used plumbers tape and adjusted it with tv outside to sat. Was 5 degrees difference. Just depends on where you rig it.
 
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LEEHRAT

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Yes I did it last year after my motor went out on my 4 ft dish. Mine is 4 degrees off from Cband. Make sure your dish it pointed at your true south location and then align your lnb from there. I get the same strenth as I had on my 4 ft dish. hope this helps
DCP 0008 1
 
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arlo

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For me it's shooting 6 degrees east of C-Band. I put the lnbf on the left of the scalar.
I have a button hook feed with a base mounting plate.
Shooting dead nuts at the center of the dish gave poor signal strength vs bouncing off it a bit right of the plate.
 

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Captain Midnight

Captain Midnight

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For me it's shooting 6 degrees east of C-Band. I put the lnbf on the left of the scalar.
I have a button hook feed with a base mounting plate.
Shooting dead nuts at the center of the dish gave poor signal strength vs bouncing off it a bit right of the plate.
I have a Ku LNBF feedhorn to play with. You can feed a typical offset LNBF into it and the tube has a Ku size scalar ring and clamp to attach it to a C band scalar. Got it for $30 from AliExpress about 18 months ago. No longer sold... But it looks nifty. I want to experiment with feeding it into a spare C band LNBF I will soon no longer need.
 

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pacificrim

pacificrim

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I did my first incarnation as a prime focus Ku with a Cband sidecar on my 7.5' Unimesh. My thinking was that the Cband was more forgiving and I could focus on Ku reception. It worked great.

Then I moved to a bigger dish - 10' KTI and a C/Ku corotor. My Ku reception is at least as good or better than on my 4' offset.
 
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mr3p

mr3p

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My initial attempt to add sidecar over weekend had mixed results although I'm hoping round 2 will have better success. A few questions:

1. Am I correct that the focal length for the Ku LNBF should be ~same as the C-band?
2. Should the Ku LNBF be slightly angled to point at the center of the reflector? Any great ideas how to verify this is just take your best guess?
3. Mount Ku LNBF as close to edge of scalar as possible?

At this point I'm thinking a couple of pipe clamps around the Ku LNBF attached to L bracket mounted on the back of the scalar
 
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arlo

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Pssst. I was in your boat. I held the lnb in my hand until I snagged a signal.
Make sure the polarity index always matches the one on the c band feed.
Tune your dish spot-on to a c band tp. Then tune to a strong ku tp on the same sat.
See if moving it around snags any sort of signal. That will give you an idea if you're in the ballpark.
Look at post #8 if you haven't. I could not get any usable signal on the same sat the dish was aimed at.
I tuned the receiver to the next ku/tp on a sat to the east (dish stays where its at).
Moved the lnb until I found a signal. As it is because you cannot get the lnb direct in line of the c band feed throat.
You will receive a signal a bit east (if you use my pic for an example) of the c band sat it's aimed at.
Yes. Get the lnbf as close to the scalar as you can. My bracket wouldn't let me.
The focal length will be close. But don't assume anything at all. It's not a hard job if you think of the reflection angle you're working with. It took probably 10 minutes for me to grab a signal after scratching my ass a few times.
Another little bit bending up a piece of aluminum and drilling the scalar for stainless steel hardware
.
When you position the dish at its highest arc the ku lnbf should be perfectly in line left and right to the c band feed.
Not higher or lower.
 
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a33

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Feb 4, 2015
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2. Should the Ku LNBF be slightly angled to point at the center of the reflector? Any great ideas how to verify this is just take your best guess?
From theory: if the Ku LNBF has a feedhorn meant for an f/D=0.6 offset dish, that is not quintessential.
The feedhorn will see only part of your dish (with f/D~0.4?), so as long as you don't aim too much to the edge of the reflector, you'd still get good reception.

When the illumination angle of the feedhorn would match the dish exactly, then you are right: the LNB should not aim exactly perpendicular to the dish face, but a bit towards the center of the dish. "A bit" is in distance about 1/3 of the sidecar-distance of the LNB, if I recall correctly.

All in all, having the LNB exactly in its (sidecar-) focal point at the correct focal length, is more important for good reception than the exact aiming direction of the LNB, I believe.

Greetz,
A33
 

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