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elements connected 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 smooths 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).
MUTE
= to turn off, to render silent. (See also SQUELCH)
N
= can be any number to solve in a classroom problem, but "N" is THE
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Unlike simpler PLL IC's, U6's phase detector has TWO outputs at pins 7 and
8. These outputs go through very simple low pass filters (R44-C68, R53-
C91) to cut back the 5 KHz whine sound of U6 at work. Op amp U5:A sums
together the phase detector outputs and the output of U5:A is passed
through a network of 2.2 uf electrolytic capacitors (C67,70,90,92) to smooth
out the phase detector pulses to clean DC for controlling the VCO.
