MGP Instruments CTM2000 Users manual

HR23x0 Theory of operation

1.1. System Architecture

A conventional superheterodyne architecture is used for this receiver. The receiver
interface is a standard RS-232 interface. The system architecture is shown in the
following block diagram.

10.7 MHz BPF
150 KHz BW

RF

130.38 MHz
BPF

IF AMP

RSSI Det

Narrow Band

1st LO

RS232

Port

PLL

IC

PLL Ref Freq

Interface

Logic

1st IF

PLL Control Lines

DDS

Synthesizer

8052 uP

80.7 MHz
2nd LO

IF AMP

10.7 MHz BPF
400 KHz BW

Radio PCB

Data Detector /

Radio Driver uP

Atmel AVR

Schlumberger Proposed Universal Receiver

Block Diag

RSSI Det

Wide Band

Frequency

Discriminator

Digital PCB

Mux /

ADC

2. Receiver Functional Architecture and Design

The drawing illustrated above shows the system block diagram The digital section
incorporates a DDS synthesizer, which will allow for fast frequency scanning.

2.1. Signal Detection / Frequency Scanning

Apex Wireless / Schlumberger Confidential 1

Since the receiver has no advance knowledge of the frequency or timing of the

v

d

F

transmitter, it must scan the frequency band in search of transmitters.

The receiver is able to implement a fast scan rate by locking a conventional LO PLL to a
fast scanning direct digital synthesizer (DDS). This technique is implemented as
illustrated below:

16 MHz

XTAL

Fref

4.043 MHz

3.986 MHz

0 ms

Microprocessor

Atmel AVR

Schlumberger Universal Receiver

DDS

AD9831

Digital PCB Ra

As the drawing above indicates, to incorporate the “fast scan” capability, the receiver uses
a DDS synthesizer IC to “drive” our conventional phase locked loop.

This technique also allows for an increase in the PLL reference frequency well above the
channel spacing (800 KHz nom) , which allows us to use a wide loop bandwidth, and
insure good tracking of the input frequency, with little “ringing” on the output frequency.

2.2. Data Detection

Fref

Di

As is indicated on the Block Diagram, data is detected using a combination of a wide and
narrow band IF filter section. The wide band filter section gives us a longer time to make
a data/no data determination during the frequency scan. For example, with the wide band
filter bandwidth of 400 KHz, a frequency sweep of 10 MHz, and a sweep time of 1.5 ms,
the data window will be 400 KHz/10MHz * 1.5ms = 60us. If the data code is guaranteed
to have an “on bit” during this window, than it will be possible to determine the presence
of a data transmitter.

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