C/Ku in same sat are at same location?

[kelleyga]

I have been getting pretty much all of the C band sats (I have 10 feet BUD,pansat3500), but when I get to one that has C band signal and Ku signal, it is harder for me to get the Ku.

1) I guess Ku is more sensitive than C band? I thought by getting C band then the Ku will be there too, just a matter of scanning.

2) Is Ku so sensitive that is my dish is not 100% aligned, I could get all C band but have little or some trouble with Ku?

 

[PSB]

1. KU is more difficult to line up than C-Band

2. Yes that seems to happen a lot!

 

[Stefan]

The beamwidth of a satellite dish is related to the size of the dish in relation to the size of the wavelength of the signal your trying to recieve with the beamwidth getting narrower as the size of the reflector with respect to the wavelength increases. This is why you always hear people say a very large dish is needed for C band. With C band the wavelength is much larger than Ku, therefore in order to have a narrow enough beamwidth to focus on a single satellite the dish must be much larger. In other words you must think of the size of your dish in terms of wavelengths and not necessarily feet or inches. Anyway, as you obviously already know (since you have a 10ft dish) to get good C band reception you need a rather large dish. When you use such a large dish and you also use that same dish for Ku, the beamwidth of this dish becomes very very narrow on Ku because in terms of Ku band wavelengths the dish is much larger. This isn't a bad thing. In fact it's quite good as it means you'll not get interference from adjacent satellites, but it also makes alignment much more critical for Ku band reception. This is the reason your observing this behavior and is to be expected with a large reflector like this. However, When you do get it well aligned you should get excellent reception.

I thought by getting C band then the Ku will be there too, just a matter of scanning.

Actually it's just the opposite. If you get your dish aligned well on Ku you can be pretty sure it's perfectly aligned on C whereas a dish can be off a good bit and still get decent C band reception because the beamwidth of the dish will be much wider on C band and even if it's off quite a bit it will still "see" the C band signals coming from the satellite. So, the best thing to do with a large dish like this is to first do a rough alignment on C band and then go back and fine tune your alignment uing Ku. When you can hit all the Ku signals in the arc and get good reception on them you'll know your fine on C.

 

[kelleyga]

Great explanation (education), Thank you