Computime CTLM901 Users Manual

4700 Duke Drive, Suite 200

Ultra-Long-Range, General Purpose

900MHz Radio Telemetry Module

12 April-2011

Revision 1.1

Cincinnati Technologies

4700 Duke Dr. Suite 200

Mason, OH 45040

4700 Duke Drive, Suite 200

900 MHz Radio Telemetry Module Description

This document describes the features and architecture for a general purpose 900 MHz
telemetry transceiver module with exceptionally long range and reliable communications.

Architecture
Radio Standard and IC Selection

The module is designed around the Atmel AT86RF212 802.15.4 transceiver IC. The

802.15.4 radio standard is an especially good choice as it provides for operation un der the
FCC CFR 15.247 spread spectrum rules, at significantly higher transmit power levels than
would otherwise be allowed. The engineers at Cincinnati Technologies have engaged in the
development of spread spectrum radio products and technologies for two decades,
beginning with the design and manufacture of the first spread spectrum residenti al cordless
telephone in 1992.

Transmit Power Level

For small, low duty cycle battery-powered applications transmitters oper ating at 50-100
milliwatts have been found to work well. It is high enough to achieve excellent range and
coverage but low enough in DC power consumption to work well with AA cells.

Data Rate and Receiver Sensitivity

The AT86RF212 transmitted data rate is software selectable from 20 kbits/second to 1000
kbits/second. Higher data rates will yield longer battery life due to shorter transmitter on
times. Lower data rates yield better receiver sensitivity and longer range. This tradeoff is
easily optimized for each application.

Integrated Diversity Antennas

The benefits gained by use of two antennas are twofold. First, in environments rich in RF
reflections, a phenomenon known as multi-path fading will frequently reduce the received
signal level. A second antenna with different radiation characteristics will have different
fades.

The second benefit is based on the fact that antennas do not perform equally in all directions.
By using two antennas with pattern nulls in different directions the module can choose to
operate with the antenna with the lowest path loss to the far end.