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SUBSCRIPTIONS & PRICING
GENERAL INFORMATION
chapter 21, Test Setups
Table of Contents
- Part 1 System Overview
- 1. WDM, Fiber to the X, and HFC Systems: A Technical Review
- Part 2 Semiconductors and Passives
- 4. Introduction to Optical Fibers and Passive Optical Fiber Components
- Part 3 RF and Control Concepts
- 9. Basic RF Definitions and IMD Effects on TV Picture
- Part 4 Introduction to CATV MODEM and Transmitters
- 14. Quadrature Amplitude Modulation (QAM) in CATV Optical Transmitters
- Part 5 Digital Transceivers Performance
- 18. Introduction to Digital Data Signals and Design Constraints
- Part 6 Integration and Testing
- 20. Cross-Talk Isolation
- 21. Test Setups
Chapter Contents
- 21.1 CATV Power Measurement Units
- 21.2 OMI Calibration Using PD
- 21.3 Two-Tone Test
- 21.4 Multitone Test
- 21.5 AGC Calibration Using Pilot Tone
- 21.6 Feedback AGC Performance Under a Video-Modulated Signal
- 21.7 Cross-Talk Test Methods
- 21.8 Understanding Analog Receiver Specification
- 21.9 Main Points of this Chapter
- References
Excerpt
21.1 CATV Power Measurement Units
In community access television (CATV), it is common to measure power by decibels relative to 1 mV in units of dBmV, rather than 1 mW in units of dBm. The ratios between decibels relative to 1 mV over 50 Ω and 75 Ω with respect to decibels relative to 1 mW systems are given by the following definitions:
• To convert dBmV to dBm: subtract 47 dB in a 50 Ω system, or 48.7 dB in a 75 Ω system.
• To convert dBm to dBmV: add 47 dB in a 50 Ω system, or 48.7 dB in a 75 Ω system.
21.2 OMI Calibration Using PD
When using a calibrated photodetector (PD) as an optical-modulation-index (OMI) calibration tool, the frequency dependency of the laser is taken into account. Furthermore, there is no need to measure the laser slope efficiency, and sometimes it is impossible. The PD is a light-controlled current source. However, it also provides two outputs, ac and dc, as shown in Fig. 21.1.
1. Photocurrent related to dc voltage measured on the internal PD (current source load) resistor Z1 (Fig. 21.1). This current is designated as Idc.
©2008 Society of Photo-Optical Instrumentation Engineers
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