mysterious delay lines

[Magnus Danielson]

>>>>> "jb" == jorgen bergfors <jorgen.bergfors at idg.se> writes:

 jb> They are probably made for delaying one scan line in PAL television sets. If I 
 jb> remember correctly, it is a plexiglass block where the signal from a transducer 
 jb> bounces a couple of times and then is picked up at the other end. It was 20 
 jb> years ago since school, where I learned this stuff. As the line frequency is 
 jb> 15625 hz, the delay time should be 64 microseconds. Or am I doing the math 
 jb> wrong?

64 us is the right delay for the PAL once's. They are used as a part
of a interesting piece of signal processing that will (for PAL but not
NTSC) among other things compensate away phase distorsions due to
ground reflections of the signals. The phase is used for color (it is
actually the angle of the color circle!). The lack of phase
compensation in NTSC is the reason that it earned it's nick-name Never
Twice Same Color sine the phase error keeps changing and banging the
poor TV set woun't help since it is not it's fault. PAL got set just a
little later than NTSC out of basically the same work and the
phasecompensation got into PAL.

Nowdays they got this funny idea of squeeze things into bits and spend
a lot more power in that compression than an PAL or NTSC encoder ever
did... in digital.

64us might not be that usefull, but maybe a couple in series and
feedback to get some sort of diffusion effect, maybe even one will do.

Cheers,
Magnus