Ericsson 19D902783G1, Руководство по обслуживанию

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CIRCUIT ANALYSIS
PRESELECTOR FILTER
The received RF signal (J2) is routed through the Prese-
lector Filter (L1 through L5). This filter provides front end
selectivity and attenuates the potential spurious signals of the
first conversion. Typically, the filter has an insertion loss of 3
dB and an operational bandwidth of 2 MHz. The filter is a
tunable, five-pole helical bandpass filter.
PREAMPLIFIER
The output from the Preselector is coupled through an
impedance matching network consisting of C1, C2 and L6 to
the base of Preamplifier Q1. The Preamplifier stage is supplied
by the reg12 Vdc line (VCC1) and draws about 80 mA.
It has a low noise figure and high Third Order Intercept point.
Transistor Q2 provides Q1 with a constant current source. The
bias on Q1 is monitored by the Fault Detector circuit via R17.
Capacitors C20 and C21 prevent any RF from entering the fault
circuit. The preamplifier output signal is coupled to the Image
Rejection Filter via an impedance matching network consisting
of C4, C11, L8, L15, R5 and R6.
IMAGE REJECTION FILTER
Following the Preamplifier is the Image Rejection Filter.
The Image Rejection Filter is a fixed tuned helical bandpass
filter. The Filter has an insertion loss of about 2 dB.
INJECTION AMPLIFIER
The local oscillator input (J3) from the Receiver Synthe-
sizer is coupled to monolithic amplifier U2, then to the base of
Q8. The Injection Amplifier, consisting of U2, Q8, and associ-
ated circuitry, is capable of amplifying the injection signal to
approximately 18 to 22 dBm. The amplifier is powered by the
reg12 Vdc line (VCC1). Transistor Q7 provides Q8
with a constant current source. The bias on U2 and Q8 is
monitored by the Fault Detector circuit via R21 and R31,
respectively. Capacitors C22, C23 and C26 prevent RF from
entering the fault circuit. The Injection Amplifier output
signal is coupled to the Injection Filter via an impedance
matching network consisting of C8, L13, and resistors R15
and R16.
INJECTION FILTER
Following the Injection Amplifier is the Injection Filter.
The injection filter is a fixed, tuned helical bandpass filter.
It is used to attenuate harmonics of the Injection Amplifier.
The filter has an insertion loss of about 2 dB.
DOUBLE BALANCE MIXER
The Double Balance Mixer (DBM) is a broadband
mixer. It converts an RF signal to the 21.4 MHz first conver-
sion IF frequency. The mixer uses low side (G9, G10) or high
side (G6, G8, G11, G12) injection driven by a local oscillator
signal. The mixer conversion loss is typically about 7 dB.
The IF output signal is then routed through a diplexer circuit
to the output connector (J4).
FAULT DETECTOR
The Fault Detector circuit monitors the operation of the
preamplifier and injection amplifier devices. Operational
amplifiers U1.1 and U1.2 compare the bias on the Preampli-
fier Q1 to preset levels, while U1.3 and U1.4 compare the
bias levels on Injection Amplifiers U2 and Q8.
When the bias for Q1, U2, and Q8 is within the preset
window limits, the output from the comparators is a logic
high level. This high level signal is sent to the Station
Controller on the FLAG 0 line.
If the biasing for the amplifiers is not within the proper
operating range, the fault detector circuit will pull the FLAG
0 line low.
Copyright© November 1994, Ericsson GE Mobile Communications, Inc.
Table 1 - General Specifications
ITEM SPECIFICATION
FREQUENCY RANGE 380 - 400 MHz (G8)
403 - 430 MHz (G11)
470 - 492 MHz (G9)
492 - 512 MHz (G10)
403 - 425 MHz (G6)
370 - 390 MHz (G12)
IF FREQUENCY 21.4 MHz
3 dB BANDWIDTH >3 MHz
IMPEDANCE 50 ohms at RF, LO, and IF Ports
CONVERSION LOSS -1.5
±
1.5dB
NOISE FIGURE (NF) <7.5 dB
THIRD ORDER INTERCEPT POINT >20 dBm (G9, G10)
>16 dBm (G6, G8, G11, G12)
IMAGE REJECTION >100dB
INJECTION POWER -1.5
±
1.5dB
TEMPERATURE RANGE -30°C TO +60°C
SUPPLY VOLTAGE 12.0 Vdc
SUPPLY CURRENT 200 mA typical
Figure 1 - Block Diagram
LBI-39129B
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