Different LNB's work better than others depending on your dish.If for example you had a 1.2m channel master dish then you would get better performances with a matched feedhorn and LNB rather than just a standard Lnb. Im sure someone can explain it in more detail
For example, most dishes are "offset" - i.e. the LNB & feedhorn are mounted on an arm at the "bottom" of the dish rather than suspended directly in the middle of the dish. This is done so that they do not obscure part of the dish's signal collecting surface. Such a dish has to point at a position of the sky below the actual satellite. The satellite signal then comes in from "above" the dish and is reflected by the dish "downwards" to the LNB. Such dishes are usually elliptical in shape with their longer edge mounted vertically so that although the dish is not pointing directly at the satellite, the satellite still sees it as a circle.
However, some dishes are not shaped like that. The most obvious exception is the Sky minidish used in the UK. That is elliptical with the longest edge being the horizontal.
The shape of the dish determines the shape of the signal as it is reflected to the LNBF. The signal is channelled through the LNBF's feedhorn to the LNB itself. To maximise the signal arriving at the LNB, the feedhorn should be geometrically matched to the dish. Hence the LNBFs used by Sky are slightly horizontally elliptical, and any other LNBF on a minidish would give slightly degraded performance.
Other than for such geometric considerations, I'm not aware of any necessity to match particular dishes to LNBs or feedhorns.
The most important differentiators between LNB(F)s are:
- type (twin? dual? quadruple? universal? c-band? etc. And related to this, the type of polarisor that may or may not be built into the LNB. For example, if you want a magnetic or mechanical polorisor, you can not use a universal LNB since they have built-in fixed polarisation probes).
- noise rating (expressed in decibels; the lower the better. A standard Universal LNB typically has a noise-rating of 0.7 to 0.8db. A "good" one will have 0.6db. Best have 0.4 or even 0.3 though they become quite expensive and there's the question of the law of diminishing returns...)
- fitting/housing (for example, although I use a universal LNB on my main dish, the dish is a Gregorian type with sub-reflector and the mounting position for the LNB will not take any old thing. When I replace my LNB, I replace JUST the LNB, and not the feedhorn. Similarly you'd have a job fixing a standard universal LNBF to the Sky minidish since Sky designed the mount especially for their own LNBF.