User's Manual
Table Of Contents
- Foreword
- Important Safety Information
- Contents
- About this Document
- Related Publications
- Product Description
- Features
- Specifications
- Air Interface
- Product Functionality
- Contents
- Integration Goal and Objectives
- Customer Problem Isolation
- Wireline and Wireless Communications
- Design Tips for Serviceability
- Environmental Issues
- Regulatory Requirements
- Contents
- Power Supply
- Host Interface
- Power Management
- Antenna Systems
- Hardware Recommendations
- Battery Selection Criteria
- Contents
- Hardware Integration
- Application Software
- Final Assembly
- Installation
- Troubleshooting
- End User Problem Resolution
- Service Depot Repair
- Contents
- Accessories and Options
- Abbreviations and Acronyms
- Desense Overview
- Desense Measurement Techniques
- Preparing the Device Under Test
- Performance Goals
- Methods of Controlling Emissions
- Antenna
- Summary
- FLEX Application Protocol Licensing
- Licensing
B-8 July 23, 2002
Appendix B CreataLink2 XT Hardware Integrator’s Guide
Performance Goals
Prediction of Sources
Typically, there are two sources of noise in a circuit, narrowband and wideband.
Narrowband interference is usually caused by a mixing product among several
sources.
If the system runs a 16.8 MHz-clock, and a 1.23 MHz-clock and a strong narrowband
emission is found at 865.2000 MHz, the emission comes from the 16.8 MHz-clock
as a product of:
865.2/16.8 = 51.5, the 51st harmonic plus a subharmonic of 8.4 MHz
The wideband emissions usually come from a switching power supply created by
the low frequency of the switcher modulating on a higher harmonic of another
source. Switching power supplies creates magnetic energy from inductive coils. Any
circuit that uses non-toroidal inductors is a source of noise.
Some emissions result from multiple order mixing of any number of sources. One
way to find the emissions is to shut down sources one by one, and see if the emission
disappears. Near-field probing provides a geographical fix on the emission when
the source circuitry is found. Noise floor problems, which desense the entire receive
band, prevent tracking individual sources by any method.
Use a loop probe to confirm emission sources. This probe must be small enough to
pinpoint the area from which the emission radiates, yet large enough to provide
adequate sensitivity.
Desense Scenarios
The target of 40 dB below FCC Class B guarantees no desensitization. Some typical
scenarios that work in favor of the system are as follows:
• The host unit is in a power management state, completely asleep or in a
reduced functional state. This state reduces EMI and enables improved
wireless communications.
• The system functions even with interference reducing coverage range. This
interference is not a problem if the data transceiver is not in a fringe area.
• Two-way protocols can retry unsent messages.
Each platform, network operating model, and user profile is different with each
application, and requires a unique level of EMI reduction effort.