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Radio Design
General Overview
The radio operates on the ETACS frequency band. The transmitter operates at
872.0125 MHz to 905.9875 MHz and the receiver at 917.0125 MHz to 949.9875
MHz. The duplex spacing is 45MHz and the channel separation is 25KHz.
Together with the logic/audio part the radio fulfills the ETACS requirements.
Antenna Connector
The antenna connector consists of a mechanical assembly that connects the antenna
to the radio. The impedance of the antenna connector is 50Ω.
Antenna Filters
The duplex filter consists of a 4-pole TX section of band pass characteristic with a
notch at the RX frequency and a 4-pole RX section filter with 50Ω impedance in
each direction.
The task for the TX filter is to suppress wide band noise evolving from the VCO and
the power amplifier on RX frequencies.
The task for the RX branch is to suppress the transmitter signal to a level low
enough not to overdrive the receiver front end amplifier and attenuate external spu-
rious signals.
The RX-section also suppresses leakage from the local oscillator.
TX
P O W E R
CONTROL
9 6 2 - 9 9 5 M H z
DUPLEX
FILTER
FRONT
E N D
Figure 6: Radio Block Diagram
TX MIXER
V C T C X O
14.85MHz
RX SYNTH
4 4 . 5 5 M H z
4 5 M H z
4 5 0 K H z
IF
Technical Description
Audio In
TX SYNTH
RADIO IF
Bus Control
BERTINDY
Audio Out
13
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