T885 Rssi Block Diagram - Tait T880 II Series Adjustment Manual

B2.12 T885 Circuit Operation
2.12 Received Signal Strength Indicator (RSSI)
(Refer to the IF section circuit diagram (sheet 3) in Section 6.2.)
The RSSI provides a DC voltage proportional to the signal level at the receiver input and
is an on-chip function of the demodulator IC (IC300). Circuitry external to IC300 condi-
tions the RSSI signal and the voltage is available at D-range 1 (PL100 pin 5).
The RSSI also provides the capability for high level signal strength muting, which may
be selected on PL250 (refer to
-115dBm and -70dBm by RV235.
Temperature
Compensation
Vref
RSSI Reference Set
The voltage offset of the RSSI signal (IC300 pin 13) is adjusted by RV345. This adjust-
ment is temperature compensated by an operational amplifier (IC351b). The signal
passes through a buffer amplifier (IC352b) before being amplified (IC352a) to give the
correct volts per dB. The amplifier is temperature compensated by IC351a and its asso-
ciated circuitry.
10/07/00
Section 3.5). The mute threshold may be set between
Demodulator
Buffer
RSSI O/P
MC3372
13
IC352b
IC351b
+
+V
RV345
Figure 2.7 T885 RSSI Block Diagram
Gain Amp.
Temperature
Compensation
IC351a
M880-00
Fixed
RSSI Output
1V/10dB
IC352a
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