EMS Wireless DataNex Data-20, User'S Reference Manual

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1-7 System Description
DataNex EMS Wireless,
DATA-20
Digital Radio
Figure 1-7. RF Upconverter Block Diagram
The IF output carrier of the IF Upconverter daughter card is fed to the transmit portion of the RF
Module via an external (rear panel) semi-rigid SMA cable. This module performs the necessary
upconversion to the RF carrier (see Figure 1-7). There is an on-board CPU for independent
control of the critical RF parameters of the system.
Since this is a linear RF processing chain, an automatic leveling control loop (ALC) is
implemented here to maintain maximum available power output (and therefore maximum system
gain). The ALC monitors the PA forward power (FWD) output sample, and controls the
upconverter gain per an algorithm programmed in the CPU. The ALC also controls the power-up
RF conditions of the transmitter output.
1.5.4
Power Amplifier (PA)
The Power Amplifier (PA) is a separate module that is mounted to a heat sink and is fan-cooled
for reliable operation. The PA is a design for maximum linearity in an amplitude modulation-
based system.
1.5.5
RF Downconverter
BPF Diplexer
70 MHz
RF Input
RF AGC
IF Amp
IF Output
70 MHz
to QAM
Demod
Preamp
ALC
Loop Amp
ALC
Det
Atten
BPF
70 MHz
PLL
Loop
Filter
VCO
PLL
Synth
Lock
Data
Clk
Enbl
Ref
ALC Control
12.8 MHz Ref Osc
uP
Synth Level
Synth Lock
NMS
Synth Clk
Synth Data
Synth Enbl
Figure 1-8. RF Downconverter Block Diagram
The receiver handles the traditional RF to IF conversion from the carrier to 70 MHz (see Figure 1-
8). Considerations are given to image rejection, intermodulation performance, dynamic range,
agility, and survivability. A separate AGC loop was assigned to the RF front end to prevent
intermodulation and saturation problems associated with reception of high level undesirable