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manual • maser 433
book, or a set of online information files, detailing
the operation and maintenance procedures for a
device or system.
manual input Use of a keyboard, mouse, trackball,
or other electromechanical input device to enter
data into a computer program or system.
manual operation In data processing, an operation
in which automatic machines are not involved.
manual telegraphy Telegraphy that consists signals
transmitted by a hand-operated key and
recorded by hand (pen, pencil, or typewriter).
manual tuning Tuning performed entirely by adjusting
variable circuit components by hand.
manual word generator A device by which an operator
can originate information words for input
into computer memory.
manufacturing automation protocol In a factory
using computer-controlled robots, the set of standards
for data communication between the
robots and the controller and/or between individual
robots. It keeps the factory operating
smoothly.
MAR Abbreviation of MEMORY-ADDRESS REGIS-
TER.
Marconi antenna A quarter-wave radio transmitting
or receiving antenna operated against an
earth ground.
Marconi effect The undesired tendency of an entire
receiving antenna system, including lead-in
or feeders, to act as a MARCONI ANTENNA.
margin
1. A gap or space between two objects,
such as adjacent plates of a capacitor. 2. Clearance.
3. The maximum error that can be tolerated
without risk of improper or abnormal operation.
4. In a teletypewriter, the range of adjustments in
which the error frequency is acceptable.
marginal relay A relay having a small difference
between its on and off currents or voltages.
marginal test As performed on equipment in a
computer installation, a test to either determine
the cause of an intermittent malfunction, or verify
an equipment’s operating tolerances.
marine broadcast station A coastal station that
broadcasts information of interest to shipping:
time, weather, ocean currents, etc.
marine radio Radio communications between
seagoing vessels or between vessels and shore
stations.
marine radiobeacon station A land-based radionavigation
station whose transmitted signals are
used for taking bearings.
mariner’s compass See MAGNETIC COMPASS.
mark 1. In telegraphy, the dot or dash portion of a
character, as opposed to the dead space between
such portions. 2. The intelligence part of a similar
signal (such as sound, light, etc.). 3. The high
(logic 1) state represented by a binary bit, as opposed
to the low (logic 0) state. 4. A character
identifying the end of a data set. Also called
MARKER (see MARKER, 2).
marker 1. A pip that indicates a particular frequency
on a response curve displayed on an oscilloscope
screen. 2. A character that identifies
the end of a data set. Also called MARK (see
MARK, 4).
marker beacons Individual coded-signal transmitters
placed along a radio range and indicating
features of the course marked by them.
marker frequency 1. A known frequency that can
be used to identify a spot-frequency harmonic of
a frequency-standard signal. 2. A known accurate
signal used to identify the limit of a radio
band. 3. The frequency at some point on a response
curve as identified by a marker pip (see
MARKER).
marker generator An oscillator that supplies a
marker pip (see MARKER).
mark hold In telegraphy, an unmodulated signal
meaning information is not being sent.
mark reading The reading by an optical scanning
device of marks made in specific areas of a document;
the process also includes the marks’ conversion
to digital signals for input to a computer.
mark scanning See MARK READING.
mark sensing A process similar to MARK READ-
ING, except that the marks are sensed electrically.
marker trap A wave trap that supplies a dip-type
marker pip when used in conjunction with a radio-frequency
test oscillator (see MARKER).
market scanner Also called bar-code reader. A device
that scans a black-bar binary label printed
on a carton or other package (or magazine), and
indicates the price of the merchandise on the
readout of the checkout register.
mark-to-space ratio In radiotelegraphy, the ratio
of the duration (mark) of a dot to the interval
(space) between successive dots.
Marx generator An impulse-type high-voltage
direct-current generator circuit in which several
capacitors are charged in parallel through a highresistance
network. When the capacitor voltage
reaches a critical high value, discharge occurs in
series through spark gaps, producing a highvoltage
pulse for each discharge.
maser A low-noise microwave amplifying device in
which a microwave input signal causes highenergy-state
molecules of ammonia or ruby to fall
to the low-energy state and, as a result, to emit
large amounts of energy as an output signal. The
name is an acronym for microwave amplification
by stimulated emission of radiation.
ac input
Marx generator