I've been out of town all week, so I come to this sobject a little later than most but heres some comments:

In reply to:


Another little story is how US NTSC (Never The Same Color ) television uses 60 fields (or 30 frames) per second. This was becuase of the US's power system being 120volts AC. The power basically became the timeing device. Someone determined that all humans really need is 45 fields per second to similate a moving image, so the 60 is really over kill and a waste of information. Needing to put out 30 frames per second, NTSC had to sacrifice scan lines per frame. In contrast, PAL uses fewer frames per second (but still enough) but allow for more scan lines. Because of this, PAL has always been considered to be better than NTSC. So it is interesting that the first TV makers in the US were not limited by their own means, but by Edison for picking the number 120. It would be interesting to go back and find out "why 120?"



PAL is considered superior to NTSC, not just because they lowered the scan rate to 50 fields/second and therefore increased the number of scan lines per field - they did this trade-off to keep the effective 'horizontal' scan rate for both NTSC and PAL the same. Hence a PAL TV set can often receive and display a black and white NTSC signal without problems.

PAL came second (NTSC was the first all-electronic TV scanning system).

Because PAL came second they had the chance to fix some of the defects with NTSC, one major one being the annoying 'loss of colour' signal phase lock, causing the whole screen field to change colour (you know those faces that flash green and back again).

They fixed this problem with PAL by making every other scan line in the field reverse/invert the colour phase signal, thus stopping those 'loss of colour' lock problems affecting all scan lines in the field (worst case it would affect 2 scan lines and the eye will blend such errors making them much less obvious).

This also gave rise to the name for PAL - it stands for something like Phase (alteration) on Alternate Lines (PAL).

the other comment about 60 fields/second, in fact NTSC runs at 59.997 fields/second or something close to stop any mains interference caused by 60Hz mains.

I can't recall why 60Hz is used, I believe Nikola Telsa (who designed the AC systems used in America today)
[Edison invented/pushed DC, Telsa invented just about everything to do with AC, single phase, 3 phase the works], picked 120 volts because it was considered much safer than any other voltage in use at the time [e.g. 200 Volts DC].

However, 60 is a multiple of lots of numbers and has a lot of factors and this fixation with 60 can be traced back to the Sumerians.
These are the guys who gave us 60 seconds a minute. 60 Minutes a hour and 360 degrees in a circle to name some things.

A bigger question is, why do the countries that have 220 Volts AC power use 50 Hertz as their mains voltage frequency and not 60?

I think that the 50/60 hertz relates to how fast the generator sets of the 19th century could be spun to make AC power, at 60 Hertz the set would need to spin at 3600 RPM, at 50 Hertz, 3000 RPM.

Regarding Railway gauges: not everywhere uses the 5 foot 10 or whatever gauge used in the US.

Here in New Zealand we use 3 foot 6 inch as our railway gauge - the reason mainly being that because this is such a rocky/mountainous/geologically active country using a smaller railway gauge meant that the diameter of the tunnels/ width of bridges/embankments/viaducts etc that had to be built could be "smaller" and thus cheaper to build.
So, because of this decision made about 140 years ago we now have a railway system which trains cannot go much above 60 mph without the trains rocking too much.
Hence Railway is not a popular freight or public transport mechanism.
Good call guys.


On a related note, the current QWERTY layout on the keyboard was (carefully) designed to prevent the typists (who used the early typewriter models) from being able to type most of the commonly adjacent letters simultaneously which could cause the keys to jam together in the first typewriters made.
[A problem which was overcome fairly quickly, but by then the QWERTY layout had become common practise].

So the QWERTY layout is in use today to overcome a mechanical design defect of the earliest mechanical typewriters designed to SLOW typists of the day down.
It has been proven that in some cases as straight alphabetical keyboard can be faster to type on than a QWERTY keyboard, but the QWERTY layout is now firmly entrenched.