to RF ground, the horizontal elements are called a "groundplane."
HIGH = In solid-state circuitry, to say a given device pin or circuit point is at a
"logic high" is to say that it shows a + DC supply voltage at that point.
Switching to the opposite state (LOW) or back again for some specific purpose
is a fundamental capability of the circuit.
HOUSE-NUMBER = A manufacturer's part number different from the industry-
standard description of a part. Example: LB3303HK (L1)
HYSTERESIS = the ability of an FM squelch circuit to remain open after being
broken by a weak signal which fluctuates further.
INPUT, INVERTING = see "Op Amp"
INPUT, NON-INVERTING = see "Op Amp"
I/O = acronym meaning "Input and Output" port or connection.
JUMPER = Short, plain wire, soldered to interconnect points in a circuit not
otherwise connected by board traces or other wiring.
KEY, "to key" = to turn on a transmitter's carrier signal momentarily, whether
by a telegraphy code key (the root of this very common radio jargon) or by a
push-to-talk switch.
L-C = A tuned circuit made of inductor (L) and capacitor (C).
LIMITER = The portion of an FM receiver circuit which chops off noise and AM
(amplitude modulation). It processes the IF signal so that only FM will be
detected.
LOCAL OSCILLATOR (LO) = An oscillator in a superhet receiver whose
output is mixed with another signal such as antenna input. See SUPERHET.
LOCK = The condition in a phased-locked-loop (PLL) in which all sections are
working together as intended and designed.
LOOP-FILTER = (See PLL). The output of a PLL phase detector is in the
form of pulses. The frequency of those pulses depends on the reference
frequency. The loop filter smoothes out these pulses into a clean DC control
voltage for the VCO. (See: VCO)
LOW = A logic level at or near zero volts. (See HIGH).
MATRIX = A methodical criss-crossing of many connections.
MC- = Prefix for parts made by Motorola, Inc.
MIXER = A circuit section which gets two or more inputs and delivers a single
output. The output is equal to the sum of the input frequencies and also to the
difference between them.
MODULATION = See also: CW, FM. "Modulation" is simply the process of
imposing variations on a steady RF signal from an audio source such as
voice, music or data (see: AFSK).
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