BRU3 LOGIC AND RADIO SYSTEM
21 (34)
BRU3 MANUAL, Doc.no: 155 16-ANNA 805 08 Uen, Rev H, 2003-02-07
6.2
Radio Units
The BRU3 Radio Unit is operated locally on site by using a VT-100 compatible
terminal, e.g., a portable PC, and FB-TEST. By using FBTEST, it is possible to
set TX and RX frequencies, transmitter power, alarm levels, parameters etc.
The BRU3 is designed for duplex traffic 8 kbit GMSK modulation. The radio
unit consists of the following main parts:
•
transmitter including synthesizer
•
receiver including synthesizer
•
modulation synthesizer
•
reference oscillator
•
radio control circuit
•
memory for radio parameters
•
filter.
6.2.1
Transmitter
The modulated output signal to the transmitter is generated by the transmitter
synthesizer. The synthesizer output signal is isolated from the transmitter power
amplifier by two buffer amplifiers. These buffer amplifiers will prevent the
power amplifiers from altering the signal when the transmitter power is
switched on.
The power amplifier supplies the desired power level from the transmitter. An
isolating device after the power module will suppress unwanted external signals
from generating intermodulation products with the transmitted signal.
A directional coupler is used to measure the output power from the transmitter
and the reflected power from the antenna. The output power from the
transmitter is controlled by an ALC (Automatic Level Control).
The modulation of the transmitter is achieved using a two point modulation
method. The VCO is modulated directly with a signal from the radio control
integrated circuit. The other modulated signal is applied to the reference
frequency input of the transmitter synthesizer.
