30 September 1988
This causes subcarrier phase to reverse every frame. Because of the extra
half cycle of the subcarrier, it takes two frames to complete one full four-
field color sequence, called a color frame.
It can be seen from the
horizontal frequency equation above, that horizontal is frequency locked to
However, it does not define the phase relationship between
Proposed color standard RS170A clearly defines SC/H phase as: the
zero crossing of the extrapolated subcarrier of color burst shall align with
the 50-percent point of the leading edge of horizontal sync (fig 3-2). For
color field one, the extrapolated subcarrier zero crossing will be positive-
going on even lines (fig 3-3). This definition of sync to subcarrier phase
(SC/H) is required for the clear identification of the four-field color
The operational ramifications of these definitions are not
obvious and require further explanation.