coefficients located in a specified zone in the
transform domain are coded. For its counter-
part, refer to threshold coding.
zonal sampling
in threshold sample selec-
tion it is difficult to transmit to the receiver
which coefficients were sent and which were
not.
In zonal coding, all coefficients are
transmitted in order of increasing spatial fre-
quency or some other predetermined order
and a end-of-block code-word is sent when
all code words are below the threshold. See
also
threshold sampl
e selection
.
zone of protection
the area of a power sys-
tem for which a particular set of protective re-
lays has primary protection responsibility. In
typical cases, operation of any of these relays
will open circuit breakers which will isolate
this zone. Each major power system compo-
nent (line, transformer, bus, generator) has a
separate zone of protection.
zone plate
a Fresnel optical circular grat-
ing that produces the spatial frequencies to
measure the resolution and the performance
of telephoto- graphic or television systems.
A moving Fresnel zone plate can measure the
performance of line- or frame-based comb
filters, the performance of scan converters,
and the scan aperture of television images.
zone recording
a technique that allows
the number of sectors per track on a magnetic
disk to vary with the radius of the track. The
tracks are divided into several zones, such
that the number of sectors per track is deter-
mined by the maximum possible bit density
on the innermost track in each zone.
ZSR
See
zero state response
.
ZVS
See
zero voltage switching
.
c
2000 by CRC Press LLC