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It sounds like you are using a Geosat Pro 3500, the Q scale on that receiver is grossly inaccurate. On mine, some TP's will read 5 and come in, switch to a different receiver and I get a reading in the 80s.

The 3500 isn't a good receiver to judge quality readings on.

Which part of the scalar should be lined up with the markings on the lnbf? The back edge of the scalar that's pointed by the arrow here? http://i.imgur.com/7XHKrXd.jpg

Thanks all.

I did read that thread earlier, out of many. Good read, but being a mechanical engineer I don't have as firm of grasp on radio wave theory. I'd love to be able to lay it out in AutoCAD like I can do with the focal point, but pure geometry doesn't seem to cut it here.

Tuning the feedhorn and scalar is like putting the cart before the horse, the way it is set up. The feedhorn pretty much needs to be set first. My calculated focal point I did put 1/4" inside the feedhorn throat. And that works out perfectly for Ku. So in order to adjust the scalar to get the proper relation to the focal point, I need to structurally modify the buttonhook.

I'm not going to rely on the markings on the side of the feedhorn, because there are different brands of dishes and scalars and feedhorns, and how they setscrew in place. Measuring my dish, my F/D works out to .30, so it looks like I should rework the buttonhook to get the inside rear face of the rings (so I read somewhere) about 1.32" from the feedhorn throat. Right now (where the buttonhook places it) is about .37" too short, and the front of the scalar is only .06" from the throat, so I can't even put the plastic cap on.

120.5" curved surface diameter
25" depth (buttonhook plate in center is flush with dish surface, not raised)
36.3" focal distance works out perfect
.30 f/D = 1.32" from throat to inside rear of scalar (please correct me if this is not right)
Rings .88" deep so 1.32" - .88" = .44" feed throat to front face of rings

I tried the .44" measurement first, which made the scalar-to-feed throat relationship proper, but had lacking Ku quality. The focal point was much more important.

I was wondering if that work would be worth it, but it sounds like I'm only utilizing a fraction of the dish and modifying the buttonhook to properly set the scalar is something I should do when it gets nicer out. I'll build some good adjustability into the modification. Definitely before spending any money on a new LNB.

That's good to know about the Geosat receiver Q scale, maybe it's not that big of a deal. My old Traxis would just max out at 80 over a large adjustment range before it dropped. The Geosat seems to be extremely sensitive and gives me an actual quality all the way up to 99, but it requires me to make much finer adjustments to get there. But these are the only two FTA receivers I've worked with.

Good to know about the Decades channel mux. I won't be pulling out what's left of my hair wondering why they might not come in sometimes.

I am not following the extra measurements and calculations between the scalar and the feedhorn settings. Not sure it is worth putting too much time into this if the scalar cannot be placed into the correct position to provide the approx. calculated focal length measurement. Probably best to initially use the matched feedhorn/scalar from a single model rather than a mixture of mismatched components to determine if the buttonhook requires modification.

With a .30 FD ratio, the feedhorn will be extended almost to the maximum distance in front of the scalar (on my sample scalar/feedhorn units the throat to the inside rear of the scalar measurement is approx. 2 1/4" for reference).

Thanks, that helps a lot. 2 1/4" is a big difference. If I just reattach the scalar to the back side of the buttonhook flange, and maintain my focal distance without modifying anything, I'll end up in the ballpark of 2 1/4". I'll do that when it gets a little warmer out and see how much of a difference it makes.

I'm pretty sure I have the Chaparral scalar somewhere. I had just used the Ma-Com scalar because it was matched to the dish. I'll have to see if there is any difference.