MC33121
MOTOROLA
29
Figure 51. Circuit Performance
820
//0.115
μ
F and 220
System
Figure 52. Return Loss Test Circuit
for Figures 46 to 51
80
100
60
–0.2
1.0 k
10 k
f, FREQUENCY (Hz)
RL
0
T
THR
+0.2
20
40
GTX
GRX
REFERENCE
NETWORK
IL
R
MC33121
CIRCUIT
(FIGURES 46,
47 OR 48)
Reference Network = RAC of Figures 46 to 48.
Return Loss = 20 log
VA– VB
VA
T
VA
VB
VB
GLOSSARY
ATTENUATION
— A decrease in magnitude of a commu-
nication signal, usually expressed in dB.
BALANCE NETWORK
— That part of the SLIC circuit which
provides transhybrid rejection.
BANDWIDTH
— The range of information carrying frequen-
cies of a communication system.
BATTERY
— The voltage which provides the loop current,
and in some cases powers the SLIC circuit. The name
derives from the fact that COs have always used batteries, in
conjunction with AC power, to provide this voltage.
BATTERY FEED RESISTANCE
— The equivalent Thevenin
DC resistance of the SLIC circuit for supplying loop current.
Traditionally it is 400
.
C–MESSAGE FILTER
— A frequency weighting which eval-
uates the effects of noise on a typical subscriber’s system.
CENTRAL OFFICE
— Abbreviated CO, it is a main tele-
phone office, usually within a few miles of its subscribers,
that houses switching gear for interconnection within its
exchange area, and to the rest of the telephone system. A
typical CO can handle up to 10,000 subscriber numbers.
CODEC
— Coder/Decoder — Interfacing between the SLIC
and the digital switch, it converts the SLIC’s transmit signal to
digital, and converts the digital receive signal to analog.
dB
— A power or voltage measurement unit, referred to
another power or voltage. It is generally computed as:
10
log (P1/P2) for power measurements, and
20
log (V1/V2) for voltage measurements.
dBm
— An indication of signal power. 1.0 mW across 600
,
or 0.775 Vrms, is defined as 0 dBm. Any other voltage level
is converted to dBm by:
dBm = 20
log (Vrms/0.775), or
dBm = [20
log (Vrms)] + 2.22.
dBmp
— Indicates dBm measurement using a psophometric
weighting filter.
dBrn
— Indicates a dBm measurement relative to 1.0 pW
power level into 600
. Generally used for noise measure-
ments, 0 dBrn = – 90 dBm.
dBrnC
— Indicates a dBrn measurement using a C–
message weighting filter.
DTMF
— Dual Tone Multifrequency. It is the “tone dialing”
system based on outputting two non–harmonic related fre-
quencies simultaneously to identify the number dialed. Eight
frequencies have been assigned to the four rows and four
columns of a keypad.
FAULT
— An incorrect condition where Tip is accidentally
connected to the battery voltage, or Ring is connected to
ground, or both. The most common fault is Ring to ground.
FOUR WIRE CIRCUIT
— The portion of a telephone, or cen-
tral office, which operates on two pairs of wires. One pair is
for the transmit path, and one pair is for the receive path.
FULL DUPLEX
— A transmission system which permits
communication in both directions simultaneously. The stan-
dard handset telephone system is full duplex.
GAIN
— The change in signal amplitude (increase or de-
crease) after passing through an amplifier, or other circuit
stage. Usually expressed in dB, an increase is a positive
number, and a decrease is a negative number.