1) The Sony method was known as 'gated NTSC' and came in two
versions; PAL-H and PAL-K. PAL-K attempted to ameliorate the
diff-phase problem by averaging over several NTSC lines, but
it gave pictures in which the colour appeared to be displaced
downwards, and (in the author's opinion) the disarmingly simple
system-H gave best results. Diff phase was never a problem unless
there was bad ghosting on the signal, and it was never a problem
with colour video playback either. In practice, with the modification
mentioned below, the decoder hue control was set once and never
touched again.
2) In order to get as far away from Telefunken's patents as possible,
Sony eschewed the 'official' method for extracting colour line
identification information (the swinging burst), and instead
used an obscure feature of the PAL signal called 'Brüch
blanking'. The problem was that Brüch blanking was optional
(ish), and some TV stations didn't always use it (it varied from
day to day at one point). The Sony decoder didn't actually care
whether it used all +(R-Y) lines or all -(R-Y) lines, but a different
setting of the hue control was required in each case, and the
line ident was required to make the choice consistent. If there
was no line-ident, there was a 50% chance that the hue control
would have to be readjusted on first locking on to a signal;
and the (commercial) stations emitting the non-standard signals
also tended to put breaks in the sync-pulse train at programme
changeovers, which threw the system out of lock and made the
Sony users keep on getting up to adjust the set every few minutes.
Modifying the decoder, to use swinging burst ident, involved
a little circuit using two diodes and a transistor (a phase-bridge
to compare the reference burst against the subcarrier oscillator,
and a transistor to reset the PAL flip-flop), which could be
tacked on to the underside of the circuit board. |
