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27.1.1999
4Z0700GB.__2
39
Product: TDP-52-SN3 (Sigma Gold) / OY0725
Receiver
OY0725 Receiver
5.3.7 General
The module contains all FM-receiver functional blocks.
When the RF signal isreceived it is brought through the duplex filter to the amplifier
stage Q101. The amplified signal is passed through the attenuator to the double-bal-
anced mixer X 102.
The upper side injection frequency is brought from the synthesizer through a small
resistive attenuator to the mixer LO pin 1 (LO = local oscillator). The 77.25 MHz
intermediate frequency from the mixer output is fed through the IF-SAW filter X102
to the FM IF-circuit I201.
RX injection frequency 540,250...544,725MHz
Injection-level/impedance +1 dBm / 50 ohm
The second intermediate-freqency local-oscillator-frequency required by the FM IF-
circuit is generated by multiplying the 12.8 MHz reference-oscillator frequency by
six. The multiplier circuit is made with transistor Q201.
The second intermediate frequency is 450 kHz. The phase-shift required by the
quadrature detector is made with the parallel-circuit L203 and C226. The detected
AF-signal temperature correction is done in the buffer amplifier stage.
RF-amplifier CF 739
1. mixer double-balanced mixer
1. IF-amplifier CF 739
FM IF system SA 607 includes the following blocks:
2. mixer
IF limiter
quadrature detector
RSSI (received signal strength indicator)