RF SIGNAL FROM
ANTENNA ON MAIN
BOARD
IF SIGNAL TO
MAIN BOARD
LOCAL
OSCILLATOR
XL201,TR203
MIXER
TR204
RF
AMPLIFIER
TR201,202
SAW
FILTER
FL201
PSG/10440/1
RPR 550IS Series
TM1188 Issue 1 Page 3 - 7
Figure 5: RPR 552IS Radio Board (Front End) Functional Block Diagram
Mixer
14. The signal frequency is fed to the base of mixer TR103, via the matching network
L101, C104 and C105, where it combines with the local oscillator output to produce a
difference frequency of 455kHz across R105. The IF signal then passes, via SK101
pin 3, to the first 455kHz IF filter, on the main board.
RPR 552IS RADIO BOARD (FRONT END)
15. Figure 5 shows the functional block diagram of the radio board (front end).
Antenna
16. The incoming RF signal is detected by the tuned loop antenna AE1 which is fixed to
both the radio PCB and the main board. Capacitors C201, C202, C203 and C204 tune
the antenna and the resulting signal is fed to the RF amplifier.
RF Amplifier
17. The signal is fed to the two-stage fixed, tuned, cascode RF amplifier TR201 and
TR202 via matching inductor L201. The amplified output then passes to the Surface
Acoustic Wave (SAW) filter via matching components L202 and R202.
SAW Filter
18. The SAW filter, FL201, has a bandwidth of approximately 100kHz and provides a
image rejection 910kHz above the channel frequency. The output, tuned by C212, is
fed to mixer TR204.
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