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-4 July 23, 2002
Appendix B CreataLink2 XT Hardware Integrator’s Guide
Desense Measurement Techniques
Desense Measurement Techniques
To measure desense indirectly, record the emission level from the host and then
calculate the effect on the data transceiver. To measure desense directly, use packet
error rate testing off the air. The direct method is similar to a system test. The test
should be non-intrusive, with no peripheral test cables connected to the unit under
test. Cables have a significant effect on receiver sensitivity results.
Indirect testing is FCC Part 15 EMI testing. Some assumptions are made to
extrapolate the results and convert them to desense figures. The best way to
measure desense is to use a spectrum analyzer to measure the signal the receive
port detects (see Figure B-2).
Connect the product antenna to a spectrum analyzer that has an input impedance
of 50 ohms. If the antenna is not available, use a portable dipole antenna as a
measurement antenna.
This measurement method determines the amount of RF energy that the host device
emits. The measurement does not account for any noise that is transmitted through
a conductive pathway.
With the input impedance of the analyzer and the antenna the same as the radio
receiver, the analyzer measures the actual receiver noise. Use the following
calculation to determine the level at which desense occurs:
Desense Threshold = Radio Receiver sensitivity [dBm] - Co-channel
rejection [dB] + Antenna Factor [dB]
Depending on its frequency, any noise source above this level can create desense.
The indirect method is less effective than the direct method because it does not
account for the characteristics of the data protocol. The bandwidth of the noise
source is important. If the source is narrowband, it may cause more problems than
a wideband source. There are only a limited number of channels available.
Therefore, a noise source that desenses a single channel can cause the data
transceiver to fail.
805SRH-26
Figure B-2. Spectrum Analyzer Setup
Coaxial Connection to Measurement Antenna
Measurement Antenna
Unit Under Test
Spectrum Analyzer
805SRH-26