The discussion centers on the behavior of electrons in Cathode Ray Tube (CRT) monitors, specifically addressing how they can be directed to precise locations despite their wave-particle duality. It is established that the electron gun fires numerous electrons, and the average trajectory results in a classical path, allowing for accurate targeting on the screen. The wave nature of electrons is statistical, and while diffraction can occur, the probability of misdirection is minimal due to the design of CRTs, including the use of shadow masks and magnetic fields for beam alignment.
PREREQUISITESPhysics students, electrical engineers, and professionals involved in display technology or quantum mechanics will benefit from this discussion, particularly those interested in the practical applications of quantum principles in electronic devices.
That was a real problem with colour TV CRT's. They had a mask with tightly spaced holes just behind the phosphorous. You had to adjust it as best you could, involving lots of compromises...sawer said:
sawer said:
sawer said:
Svein said:
sawer said:
That wasn't a problem of QM. The dimensions of an electron gun (and the whole CRT) take matters way out of the region of diffraction. Any beam spreading and also the resulting lack of colour purity is down to the very tight margins for a shadow mask (and the subsequent improvements) and the fields which deflect the electron beam. Electrons can be treated as 'simple' charged particles when you're designing electron optics in this context, I'm sure.Svein said:
Possibly not, but wave interference was a real problem. TV presenters were not allowed to wear clothes with fine patterns...Drakkith said:
It was due to limitations of PAL and NTSC as well as interlacing jitterSvein said:
OMG. That's a bit of a wild guess; the orders of magnitude are all wrong for diffraction.Svein said:
It's to do with the colour coding on the signal and it's there on the drive to the tube. In PAL and NTSC, there is a 'subcarrier' at 4.43MHz (PAL), which carries the colour (chrominance) information. This subcarrier forms beats with high frequency video components. These beats are whet you see when the picture content is stripy. A 4.2 MHz grille will produce 230kHz fringes - very visible. The effect is not as visible on single sharp edges so the picture is ok if you avoid regular hf patterns.A detail that the diagram does not show is that the three beams have to come from the same virtual point in space, despite the electron guns and grids are fairly wide, so the shadow mask works onver the whole screen. (Also, the beams go through more than just one hole at a time to make the picture bright enough). The beams from the three guns have to be bent by magnetic fields to achieve this. No wonder those shadow mask tubes had to be set up every day for high quality stdio use. TGF LCDs.Svein said:
Svein said:
Vanadium 50 said:
The shirt problem was intermodulation, whatever he means. It happened on flat screen PAL receivers.Drakkith said:
The holes were close enough to create an optical grid...Drakkith said:
What wavelength would you assign to the electrons, though?Svein said: