Rick's b.log - entry 2014/12/08

Dumb things seen at the supermarket

Secondly, the French have really taken to misplaced apostrophes (and as somebody who used to be irritated with "fish and chip's" written on pub menus, this really grates), however this particular little amusement made me really glad that I had a camera to hand:

Next up: This isn't supermarket dumbness this time, but it is dumb and it is in the supermarket. What, you ask? KitKat Singles. Say whut? Individually wrapped single KitKats. This just really seems to me to be trying to solve a problem that didn't really exist. KitKat has been around since 1935 (owned by Nestlé since 1988 - yes, I wiki'd it) and we've done just fine with breaking as much as we want from the four-finger bar. Is this a "health" thing? Because, trust me, I don't think eating KitKat in singles is going to keep you slim. There is so much rubbish in processed foods, and so many people eat these, and so few people eat real actual vegetables that going a stage further and omitting chocolate entirely won't suddenly make you thin again. Plus, I don't like to be nannied, so pass me a KitKat Chunky, thanks...
By the way, Wiki also says: In Japan, Nestlé has introduced over 200 different flavours since 2000, including ginger ale, soy sauce, creme brulee, green tea, and banana.
Oi! Nestlé! How about some of that over this side of the world? Okay, I really can't imagine what a soy sauce chocolate bar would be like, but crème brulée and banana sound nice. I have tried a Japanese KitKat mini, it was in a brown wrapper and it was quite pleasant. Dark chocolate? I don't know, it was written in Kanji... <sigh!>

And, finally, this (note the highlighted word):

STOP PRESS!

Wow. That's a seriously Blue Peter way of doing things.

Sadly, now to burst the bubble. At the frequencies used in the Ku band (that is, 10-12GHz), the dish surface needs to be created with an accuracy of less than two millimetres (about a tenth of the wavelength) across the entire dish surface; for the dish acts as a lens focusing the incredibly weak signals into the LNB's horn. It is not a straight parabola, but is something quite a bit more complicated - take a look at the position of the LNB and try to guess what is going on there. [hint: the dish itself does not point at the satellite, the signals come from above]
Any deviations here will be a mis-focus. At best, it will be like a short-sighted person without their glasses. However, if the dish is uneven, it is entirely possible to have stray signals from other satellites entering the LNB in addition to those from the satellite that you want. To give an idea of the accuracies required here - to receive Hotbird (13°E) and European TV on old Astra (19.2°E), you need to buy a special LNB commonly called a "monobloc" over here. This is because the focus from the two satellites are so close together that you cannot physically mount two standard LNBs side by side. I tell you this not to show off my knowledge, but to point out that there are other satellites between Hotbird and Astra. Stray signals? Count on them.
This is why few people ever make their own DIY dish, and why a cheap looking dish is expensive. Anything less than accurate will not be tolerated by the system.
Now for the real kicker. You cannot convert a 45cm dish to a 60cm dish just by adding some chicken wire. At best, you will have a 45cm dish with a pretty border. The reason for this is that the LNB's feed horn has a specific "field of view". It will "see" the 45cm part of the dish, exactly as the manufacturers intended. And it will see no more. You could correctly mount the LNB inside a radio telescope to have a fifty metre dish....the LNB will still only see 45cm of it.
You cannot simply extend the arm that the LNB is affixed to, as this will throw the entire alignment out. The arm will need to be removed, the correct angle calculated (to a tolerance of less than a degree in both axes) and a new longer arm made up to place the LNB in the required position. If anything is out of line, even by an amount to tiny as to be hard to measure with household equipment, the end result of a DIY 60cm dish will be worse than a generic 45cm dish.

It was a good idea - don't get me wrong about that - it's just unfortunately an idea that doesn't quite appreciate the vast pile of scary maths behind it all. As I said, there's a reason people don't DIY their own dish (or dish extensions) in the Ku band.

Day eight

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