18WuD2x

Zener knee • zero capacitance 767
standardization, the knee should be as sharp as
possible.
Zener knee current In a Zener diode, the current
that flows when the reverse bias reaches the
avalanche voltage.
Zener-protected MOSFET See GATE-PRO-
TECTED MOSFET.
Zener voltage The particular value of reverse voltage
at which a Zener diode or other reversebiased
pn junction abruptly exhibits the
avalanche effect. Depending on the Zener diode,
this potential can be less than 10 volts, or as
much as several hundred volts.
zenith In the sky, the point directly overhead, exactly
180 degrees opposite the direction of the
earth’s center.
Zeolite process A method using certain artificial
Zeolites (hydrous silicates) to soften water used in
some electronic manufacturing and testing operations.
zeppelin antenna Also called zepp. 1. A half-wavelength
radiator, fed at one end with a quarterwavelength
section of open-wire line. The feed
line can come away from the radiator at any
angle, usually 90 degrees or more. The antenna
was originally used aboard zeppelins; the entire
system was dangled in flight and the feed line was
collinear with the radiating element. The
impedance at the feed point is high; the
impedance at the transmitter end of the feed line
is low. The antenna will operate satisfactorily at all
harmonics of the design frequency. 2. A radiator
that is an integral multiple of a half wavelength,
fed with open-wire line of any length. A transmatch
is employed at the transmitter and of the
feed line. This arrangement is popular among radio
amateurs. The primary advantage of this an-
Antenna
tuner
Parallel-wire
line
Radiator
n(λ/2)
n = 1,2,3 . . .
zeppelin antenna
tenna is ease of installation; the main drawback
is the fact that the feed line radiates to some extent
because the system is not perfectly balanced.
zero 1. The number represented by the cipher
symbol (0). 2. To set a meter or other instrument
to its zero reading or condition. 3. To align one element
of a system precisely with another. 4. In
computer operations, to set a register to zero.
5. In computer operations, using zero pulses to
replace what is in a storage area.
zero-access memory See ZERO-ACCESS STOR-
AGE.
zero-access storage Computer storage requiring
negligible waiting time (latency).
zero-address instruction A computer instruction
requiring no address; the operation specified by
the instruction defines the locations of the
operands. Also called addressless instruction.
zero adjust In an analog metering device, a mechanical
or electrical control that allows precise
setting of the reading to zero, when the parameter
to be measured is actually zero.
zero adjustment 1. The act of setting an instrument
or circuit to its zero reading or zero-operating
condition. 2. A device or subcircuit used to
set a meter to its zero reading. Also see ZERO
SET, 1, 2.
zero-angle cut An alternate term for X cut, as applied
to quartz crystal plates. Also see CRYSTAL
CUTS.
zero axis In a plot of a variable quantity, the (usually
horizontal) reference line that indicates the
zero value of the quantity.
zero-axis symmetry The condition in which a
waveshape is symmetrical about a zero axis.
zero beat
Complete absence of a beat note (i.e., silence),
a condition occurring when the frequencies
of the beating signals (or their harmonics) are
equal. See BEAT NOTE.
zero-beat detector A device or circuit used to
sense and indicate the condition of zero beat.
zero-beat indicator See ZERO-BEAT DETECTOR.
zero-beat method A means of adjusting the frequency
of one signal exactly to that of another
(usually standard) signal by setting the first signal
frequency to zero beat with the second signal
frequency.
zero-beat reception A system of reception entailing
zero beating an incoming signal with the signal
from a local oscillator. Also called homodyne
reception.
zero-bias operation Operation of a transistor or
vacuum tube without direct-current base, gate,
or grid bias.
zero-bias tube A vacuum tube designed for operation
(particularly in a class-B power amplifier)
without direct-current grid bias. In such a tube,
the zero-signal plate current is very low because
of the large amplification factor.
zero capacitance 1. Absence of capacitance (a
theoretically ideal condition). 2. In some circuits,