VHF 5000 System Functional unit description
1-3
0608
The module is connected to two antennas. One for voice communications and one for DSC reception only.
Transmitter
The AF signal from the base band module is led directly as modulation signal to the transmitter VCO. This signal
is amplified in the power amplifier and led to the antenna through the RX/TX antenna shift relay.
Receivers
The DSC receiver is dedicated to listen to all communication on channel 70 independent of the main receiver.
The main receiver is listening on the channel selected by the user.
Both receivers are designed in the same way as a super heterodyne. In front it has a sturdy 1
st
mixer ensuring
good intermodulation and blocking immunity. The IF section is with no adjustable coils. In fact the receiver has
no adjustment at all.
The 2
nd
mixer and 2
nd
IF section ensures good selectivity. The IF frequency of 450 kHz is filtered and
demodulated to AF signal which is led to the Base Band for further handling.
Synthesizers
There are three synthesizer sections. One for each receiver and one for the transmitter.
The synthesizers are designed of the Phase Locked Loop principle and they are all locked to a temperature
stabilized reference frequency of 14.85 MHz.
Duplex
In duplex version the receivers and the transmitter are working simultaneously. The main receiver and the
transmitter frequency is separated by 4.6 MHz. Through a duplex relay the transmitter and the main receiver
is connected to a duplex filter ensuring good duplex performance.
This module is adjusted in full at the factory and should not be adjusted again.
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