DOCSLIB.ORG

Virtual Instrumentation Performs Dbrnc Noise Measurements

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Virtual Instrumentation Performs Dbrnc Noise Measurements MEASUREMENTS Telephony Virtual Instrumentation Performs dBrnC Noise Measurements by Craig Rupp, Senior Electrical System involved the use of SCXI™-1120, coupled One common specification found in Engineer, Alliance Technologies Group with data acquisition. For the complex telephony applications is dBrnC – the dBrnC measurement, purchasing an amount of noise measured through this The Challenge: Performing expensive audio analyzer with excess C-message-weighted filter relative to a dBrnC noise measurements on functionality was unnecessary. reference noise level of 1 picoWatt. A several power supply test stations. simple approach to performing the dBrnC The Solution: Synthesizing the measurement is to purchase a filter digitally using the LabVIEW After reviewing the client’s test commercially available audio analyzer. ™ Advanced Analysis Toolkit, SCXI signal requirements, we found that the This audio analyzer performs the dBrnC conditioning, and data acquisition. most cost-effective solution for measurement but also includes functions unnecessary for PCP’s application. Introduction measuring the voltage regulation, Because PCP only required one function Power Conversion Products (PCP), a efficiency, and power factor involves from this instrument, that measurement leading manufacturer of high-power the use of SCXI-1120, coupled with had a high price tag. switchmode rectifiers for the data acquisition. Having unused channels and jumper- telecommunications industry, hired selectable gains, the SCXI-1120 and Alliance Technologies Group (ATG), a Because the human ear is not equally MIO DAQ board provided a method for National Instruments Alliance Program sensitive to all voice frequencies and obtaining an amplified, isolated, digital member, to develop an automated test because telephone handsets do not have a representation of the signal. Using the system for its Twinpack Plus 2.5 kW flat electrical-to-acoustical frequency LabVIEW Advanced Analysis Toolkit, we rectifiers. The test system needed to response, not all frequency components synthesized the C-message-weighted filter measure the performance of the rectifier of noise are equally objectionable. In the digitally and incorporated the dBrnC including voltage regulation, efficiency, 1960s, Bell Labs devised a noise- measurement with virtual instrumentation. power factor, and dBrnC noise over weighting filter to correlate measurements various line and load conditions. with a listener’s subjective assessment. Measurement Process This frequency response, called a Simulations showed the most efficient and System Components C-message-weighted filter, has a 0 dB accurate method of implementing the After reviewing PCP’s test requirements, reference at 1 kHz with components filter involved first computing the power we found that the most cost-effective above and below this frequency spectral density of the input signal. solution for measuring the voltage attenuated to match the response of the Integrating the output over all frequencies regulation, efficiency, and power factor ear and telephone handsets. then derives the output power. fs, Hz DBL df 2.0 X power, dBrn ti 1 1 x x(+)d± 1 Y to input samples X Y 1 10 x DBL Hanning Numeric Integral LOG [DBL] x Trapezoidal Rule 600.0 1E-12 10.00 Hanning Offset Gain 2 N [] x THRESH 0 [] C Message Filter Attenuation i 10 H(f) 0..N N..0 1 INTERP 10 X 1 1 -20.0 LabVIEW code implementing dBrnC measurements. 30 National Instruments Tel: (512) 794-0100 • Fax: (512) 683-9300 • [email protected] • www.ni.com/telecom MEASUREMENTS Using a sampling rate of 40 kHz, a total 24 Vrms, a low-level signal. Maintaining of 8,192 input samples were windowed the maximum ± 5.0 V rails over the SCXI LabVIEW with a Hanning window. This reduces the interface and using the 12-bit MIO Evaluation spectral leakage that occurs when board, we computed that the Package computing the power spectral density quantization noise would be 10 dB below found in using a straight boxcar window. the lowest level signal with gains ranging The input samples are gain-corrected from 116 to 1479. By using a gain value because the Hanning filter attenuates the in the SCXI-1120 near the minimum, input samples by a factor of 1.64. The there would be plenty of headroom Hanning-filtered samples are then taken available for any high-level signals The LabVIEW Evaluation outside the C-message-weighted filters Package includes a free, fully- bandwidth but prior to the digital filter. functional LabVIEW Because the signal measured has an Evaluation CD with which The advanced analysis capabilities appreciable DC component, it was users can do tutorials, run of LabVIEW gave us the ability to necessary to add a blocking capacitor sample programs, and learn to implement the single dBrnC with a low leakage current. A large build virtual instrumentation measurement in a system that leakage current can cause an excessive applications for a variety of DC bias that takes away from the telecom applications. already contained DAQ products. headroom in the converter. We used the LabVIEW graphical 10 kHz filters on the SCXI-1120 for programming software is through the auto power spectrum VI. antialiasing and to help attenuate the available for Windows The C-message filter is frequency frequency components above 10 kHz. NT/95/3.1, Macintosh, Sun, interpolated to match the frequency bin With this network, an SCXI-1120 gain of HP-UX, and Concurrent size of the input power spectral 200, and the 12-bit MIO board, we found PowerMAX. density. The result is then squared and the noise floor of the measurement system multiplied by the input power spectral to be at –12 dBrnC. Order the evaluation package density and integrated. This result is then by calling (800) 258-7022 or referenced to 600 ohms and to the Results downloading the program reference noise of 1 picoWatt. The advanced analysis capabilities of online at PCP’s maximum and minimum noise LabVIEW gave us the ability to ni.com/labview/lv_dl.htm levels were 30 and 0 dBrnC respectively. implement the single dBrnC As a rule of thumb, we kept the measurement in a system that already quantization noise floor from the contained DAQ products. The resulting converters at least 10 dB below the product increased performance and smallest signal. This results in a required reduced costs.1 dynamic range of at least 40 dB. Given a 12-bit MIO board in the system, this gave For more information, contact Craig Rupp, a dynamic range of 72 dB, easily meeting Alliance Technologies Group, www.ni.com/labview the requirement. 1017 Butterfield Road, Vernon Hills, IL 60061, With a 0 dBrnC signal across a tel (847) 247-9284, fax (847) 247-9724, telephony-standard impedance of e-mail [email protected] 600 Ω, the minimum voltage would be at National Instruments 31 Tel: (512) 794-0100 • Fax: (512) 683-9300 • [email protected] • www.ni.com/telecom.
Load more

Recommended publications
  • Spectrum Management Technical Handbook
    NTIA TN 89-2 SPECTRUM MANAGEMENT TECHNICAL HANDBOOK TECHNICAL NOTE SERIES NTIA TECHNICAL NOTE 89-2 SPECTRUM MANAGEMENT TECHNICAL HANDBOOK l U.S. DEPARTMENT OF COMMERCE Robert A. Mosbacher, Secretary Alfred C. Sikes, Assistant Secretary for Communications and Information JULY 1989 ACKNOWLEDGEMENT NT IA acknowledges the efforts of Mark Schellhammer in the completion of Phase I of this handbook (Sections 1-3). Other portions will be added as resources are available. ABSTRACT This handbook is a compilation of the procedures, definitions, relationships and conversions essential to electromagnetic compatibility analysis. It is intended as a reference for NTIA engineers. KEY WORDS CONVERSION FACTORS COUPLING EQUATIONS DEFINITIONS ·TECHNICAL RELATIONSHIPS iii TABLE OF CONTENTS Subsection Page SECTION 1 TECHNICAL TERMS:DEFINITIONS AND NOTATION TERMS AND DEFINITIONS . .. .. 1-1 GLOSSARY OF STANDARD NOTATION . .. 1-13 SECTION 2 TECHNICAL RELATIONSHIPS AND CONVERSION FACTORS INTRODUCTION . .. .. .. 2-1 TRANSMISSION LOSS FOR RADIO LINKS . �. .. .. 2-1 Propagation Loss . .. .. .. 2-1 Transmission Loss ........................................ 2-2 Free-Space Basic Transmission Loss .......................... 2-2 Basic Transmission Loss .................................... 2-2 Loss Relative to Free-Space .................................. 2-2 System Loss . .. 2-3 ; Total Loss . .. .. 2-3 ANTENNA CHARACTERISTICS . .. 2-3 Antenna Directivity ........................................ 2-3 Antenna Gain and Efficiency .................................. 2-3 I
    [Show full text]
  • NORTHERN ENGINEER a Publication of the School of Engineering
    THE NORTHERN ENGINEER a publication of the school of engineering ""-·, • •• 4/ltlll .. Volume 23, Number 2 & 3 u NIVERSilY OF ALASKA FAIRBANKS .. Summer/Fall 1991 ADVISORY BOARD e are a reflection of our times. For THE NOKTHERN W ENGINEER, the University of Alaska, the State of Alaska, the Robert Boswell Lake & Boswell United States ofAmerica, and even the world as a whole, this is a time Fairbanks, AK of transition. The University of Alaska Fairbanks, of which THE AndrieChen NOKTHERN ENGINEER is a part, is undergoing a reorganization with Exxon Production the intent being to create a more streamlined, stronger entity, better Research Company Houston, TX able to meet the needs of our many constituencies. Mark Fryer Fryer/Pressley How will these changes affect THE NOKTHERN ENGINEER? Engineering, Inc. Anchorage, AK Well, one change has already occurred, Cynthia M. Owen left the Wilbur Haas University ofAlaska Fairbanks, effective June 30, 1992. This is the last Michigan Technological University issue that Mrs. Owen collaborated on--editing, proofing, Houghton, MI brainstorming. She contributed greatly to the quality of this publication Lee Leonard and will be sorely missed. U.S. Department of Energy Washington, DC The next part of this change will be the need for us to address the problems of THE NOKTHERN ENGINEER. We have been facing a Ed Link U.S.CRREL decline in paid subscribers, dijficulty in obtaining publishable technical Hanover,NH material and severe budgetary constraints. For all of these reasons, MikeMetz THE NORTHERN ENGINEER will temporarily suspend publication, Yukon Pacific Corporation effective the Winter 1991/Spring 1992 issue.
    [Show full text]
  • 3510 33 P Department of Commerce
    This document is scheduled to be published in the Federal Register on 08/15/2017 and available online at https://federalregister.gov/d/2017-16904, and on FDsys.gov Billing Code: 3510 33 P DEPARTMENT OF COMMERCE Bureau of Industry and Security 15 CFR Parts 740, 772, and 774 [Docket No. 170309249-7249-01] RIN 0694-AH35 Wassenaar Arrangement 2016 Plenary Agreements Implementation AGENCY: Bureau of Industry and Security, Commerce. ACTION: Final rule. SUMMARY: The Bureau of Industry and Security (BIS) maintains, as part of its Export Administration Regulations (EAR), the Commerce Control List (CCL), which identifies certain items subject to Department of Commerce jurisdiction. This final rule revises the CCL, as well as corresponding parts of the EAR, to implement changes made to the Wassenaar Arrangement 1 List of Dual-Use Goods and Technologies (WA List) maintained and agreed to by governments participating in the Wassenaar Arrangement on Export Controls for Conventional Arms and Dual-Use Goods and Technologies (Wassenaar Arrangement, or WA) at the December 2016 WA Plenary meeting. The Wassenaar Arrangement advocates implementation of effective export controls on strategic items with the objective of improving regional and international security and stability. This rule harmonizes the CCL with the agreements reached at the 2016 Plenary meeting by revising Export Control Classification Numbers (ECCNs) controlled for national security reasons in each category of the CCL, as well as making other associated changes to the EAR. DATES: This rule is effective [INSERT DATE OF PUBLICATION IN THE FEDERAL REGISTER], except that: 1. the effective date for amendatory instruction 30 (ECCN 4A003 in Supplement No.
    [Show full text]
  • Biasing Techniques for Linear Power Amplifiers Anh Pham
    Biasing Techniques for Linear Power Amplifiers by Anh Pham Bachelor of Science in Electrical Engineering and Economics California Institute of Technology, June 2000 Submitted to the Department of Electrical Engineering and Computer Science in partial fulfillment of the requirements for the degree of Engineering and Computer Science Master of Engineering in Electrical 8ARKER at the &UASCHUSMrSWi#DTE OF TECHNOLOGY MASSACHUSETTS INSTITUTE OF TECHNOLOGY JUL 3 12002 May 2002 LIBRARIES @ Massachusetts Institute of Technology 2002. All right reserved. Author Department of Electrical Engineering and Computer Science May 2002 Certified by _ Charles G. Sodini Professor of Electrical Engineering and Computer Science Thesis Supervisor Accepted by Arthuf-rESmith, Ph.D. Chairman, Committee on Graduate Students Department of Electrical Engineering and Computer Science 2 Biasing Techniques for Linear Power Amplifiers by Anh Pham Submitted to the Department of electrical Engineering and Computer Science on May 10, 2002 in partial fulfillment of the requirements for the degree of Master of Science in Electrical Engineering and Computer Science Abstract Power amplifiers with conventional fixed biasing attain their best efficiency when operate at the maximum output power. For lower output level, these amplifiers are very inefficient. This is the major shortcoming in recent wireless applications with an adaptive power design; where the desired output power is a function of the bit-error rate, channel characteristics, modulation schemes, etc. Such applications require the power amplifier to have an optimum performance not only at the peak output level, but also across the adaptive power range. An adaptive biasing topology is proposed and implemented in the design of a power amplifier intended for use in the WiGLAN (Wireless Gigabits per second Local Area Network) project.
    [Show full text]
  • The Db Concept
    Chapter | six The dB Concept CHAPTER OUTLINE dBdPower Ratio..................................................................................................................... 40 dBdAmplitude Ratio.............................................................................................................. 40 From dB to Power or Amplitude Ratio............................................................................ 41 Conversion Table ....................................................................................................................... 41 Reference Values ...................................................................................................................... 41 Other Relative Units ................................................................................................................43 Weighted Measurements....................................................................................................... 44 Addition of dB........................................................................................................................... 44 Nomogram (Addition)..........................................................................................................................44 Subtraction of dB......................................................................................................................45 Nomogram (Subtraction) ...................................................................................................................46 When sound levels have to
    [Show full text]
  • Agilent 89441A Vector Signal Analyzer Dc to 2.65 Ghz Data Sheet
    Agilent 89441A Vector Signal Analyzer dc to 2.65 GHz Data Sheet Definitions Introduction Analog demodulation mode = Measurements with AM, Specifications describe warranted performance PM, and FM demodulation capabilities. over the temperature range of 0° to 45°C (except where noted) and include a 30-minute warm-up Baseband = dc to 10 MHz measurements. from ambient conditions, automatic calibrations enabled, auto-zero on, time domain calibration off, Baseband time = Time-domain measurements selected and anti-alias filter in, unless noted otherwise. by setting start frequency to exactly 0 Hz or choos- Supplemental characteristics identified as “typical” ing full span in 0 to 10 MHz measurements. or “characteristic” provide useful information by giving non-warranted performance parameters. dBc = dB relative to input signal level. Typical performance is applicable from 20° to 30°C. When enabled, automatic calibrations are periodi- dBfs = dB relative to full scale amplitude range cally performed to compensate for the effects of setting. Full scale is approximately 2 dB below temperature and time sensitivities. During the cali- ADC overload. bration, no signals > 0 dBm should be connected to the front panel inputs. FS or fs = Full scale; synonymous with amplitude range or input range. Feature summary RBW = Resolution bandwidth. Frequency dc to 2.650 GHz RF = 2 MHz to 2.65 GHz measurements. 51 to 3201 points Center frequency signal-tracking Scalar mode = Measurements with only frequency- Instrument modes domain analysis available. Frequency spans up to Scalar (frequency-domain only) 2648 MHz. Vector (amplitude and phase information in frequency and time domain and also SNR = Signal to noise ratio.
    [Show full text]
  • 53742 Federal Register / Vol
    53742 Federal Register / Vol. 83, No. 206 / Wednesday, October 24, 2018 / Rules and Regulations DEPARTMENT OF COMMERCE Categories 7 & 9: Michael Rithmire ECCN change to maintain NP 202–482–6105 or Michael Tu 202–482– controls: 2B206. Bureau of Industry and Security 6462. Category 9x515 (Satellites): Michael Category 0—Nuclear Materials, 15 CFR Parts 740, 742, 744, 772, and Tu 202–482–6462. Facilities, and Equipment [and 774 Category ‘‘600 Series’’ (Munitions Miscellaneous Items] Items): Christopher Williams at 202– [Docket No. 170831854–7854–01] 0A617 Miscellaneous ‘‘Equipment’’, 482–6023 or Heather Moore at 202–482– Materials, and Related Commodities RIN 0694–AH44 4786. ECCN 0A617, paragraph y.3, SUPPLEMENTARY INFORMATION: Wassenaar Arrangement 2017 Plenary containers for shipping or packing Agreements Implementation Background defense articles or items controlled by The Wassenaar Arrangement ‘‘600 series’’ ECCNs, is amended by AGENCY: Bureau of Industry and narrowing the scope to International Security, Commerce. (Wassenaar or WA) (http:// www.wassenaar.org/) on Export Organization for Standardization (ISO) ACTION: Final rule. Controls for Conventional Arms and intermodal containers or demountable vehicle bodies (i.e., swap bodies), but SUMMARY: The Bureau of Industry and Dual-Use Goods and Technologies is a also expands the scope beyond Security (BIS) maintains, as part of its group of 42 like-minded states ‘‘specially designed’’ by adding ‘‘or Export Administration Regulations committed to promoting responsibility modified’’. As the term ‘modified’ is in (EAR), the Commerce Control List and transparency in the global arms (CCL), which identifies certain items trade, and preventing destabilizing single quotes, BIS is also adding the subject to Department of Commerce accumulations of arms.
    [Show full text]
  • Audio Metering
    Audio Metering Measurements, Standards and Practice This page intentionally left blank Audio Metering Measurements, Standards and Practice Eddy B. Brixen AMSTERDAM l BOSTON l HEIDELBERG l LONDON l NEW YORK l OXFORD PARIS l SAN DIEGO l SAN FRANCISCO l SINGAPORE l SYDNEY l TOKYO Focal Press is an Imprint of Elsevier Focal Press is an imprint of Elsevier The Boulevard, Langford Lane, Kidlington, Oxford, OX5 1GB, UK 30 Corporate Drive, Suite 400, Burlington, MA 01803, USA First published 2011 Copyright Ó 2011 Eddy B. Brixen. Published by Elsevier Inc. All Rights Reserved. The right of Eddy B. Brixen to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988 No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangement with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein.
    [Show full text]
  • The Following Are Some of the Questions Raised During Our Classes and My Answers to Them
    The following are some of the questions raised during our classes and my answers to them. Don’t trust my answers all the times. You are welcome to question, challenge and discuss about them. Question #1: What is the real meaning of the k-factor? When is it positive, negative and infinite? My answer: The k-factor is a measurement of the effective earth radius when the normally-non-straight radio line-of-sight path is considered. In other words, the k-factor measures how the earth curvature you “see” when you “fly” like radio waves along the radio path and consider yourself flying in a straight line. That is, the k-factor gives us the relative curvature of the real earth in reference to the radio path if it is considered as a straight line. To compute the k-factor, the original system is redrawn in such a way that the radio path becomes straight. Correspondingly, the curvature of the earth will be changed. The changed earth is then considered as the effective earth. The ratio of the radius r of the effective earth to the radius of the real earth ro is then considered as the k factor. If the centre of the effective earth is on the same side of the real earth, the k is positive; otherwise it is negative. The following figures illustrate the concept: Terminology: transmission level point (TLP): In a telecommunications system, a test point, i.e., a point where a signal may be inserted or measured, and for which the nominal power of a test signal is specified.
    [Show full text]
  • J Pole - 4 Supper J Pole - 5 Slim Jim Antenna 1 1\4 - 6 Collener - 7 Discone - 8 Marconi Vertical Antenna - 9 Bazooka Antenna -10
    . Antenna . Wave length ( ) 5% . 0.66 (velocity factor) RG-58 300 000 Km/s . = C , = F : = 120 Impedance ) . ( . ( ) 50 . , ( ) . 50 ( ) . 50 VSWR and Reflected Power SWR VSWR VSWR . ( ) 2:1 ( Voltage Standing Wave Ratio ) VSWR ) 1.5:1 1.5:1 VSWR 100 Watt ( 1:1 4 Watt 96 Watt . 4.2 Band Width . SWR , , , . 121 . : 150 MHz . 825 MHz 450 MHz : Band Width ( 150 – 156MHz ) ( ) . 3.9% BW = 100 X Fh – Fl Fc BW = 100 X 156 150 = 3.9 % 153 Decibel ( ) . 122 A . B . ( gain ) B A ( loss ) B A ( Isotropic ) dBi -1 . dBd -2 . 2.14 dBi = 0 dBd dBq -3 . , dBc -4 . ( side band peak power) dBm -5 . 50 v dB v -6 0dB v 50 1 v . dB(old) -7 0 dB 500 6mv 600 mv1 VU . 123 dBm dBw -8 - 30dBw = 0 0dBw = +30dBm . 1 . 0.775 V VRMS dBu -9 1 V dBv -10 , Milivolt dBmv -11 0dBmv 1mv 75 1mv . ( snow ) (Sound Pressure Level) dB(spl) -12 20 micropascals . 1 µPa . ( ) (Sound Intensity level) dB(sil) -13 ) / 10^ -12 . ( (Sound Power Level) dBswl -14 . 10^ -12 dB(C) / dB(B) / dB(A) -15 . 20 µPa dB(spl) dB(C). / 1 = 1 dBj -16 . 0dBj =0dBw/Hz ( Noise Density ) 1 µv / m dBµ -17 . ( / 1 ) . 1 femtowatt dBf -18 124 . 1Kilowatt dBk -19 0dBfs , dBfs -20 . Digital system 1 ( overload ) dBo -21 . analog system dBfs 1 bandwidth dB-Hz -22 . 20dB-Hz = 100Hz , Link budget calculation ( isometric circular ) dBic -23 . ( reference noise ) dBrn -24 Directivity and Gain . , 100 , 100 . , G = x D G = = D = 125 Gain measurement ( ) .
    [Show full text]
  • The Telephone Network
    TheThe TelephoneTelephone NetworkNetwork An Engineering Approach Ref: Digital Telephony (John Bellamy) and Fundamentals of Telecommunications (R. L. Freeman) Introduction to Telecommunications Network Engineering (Second Edition), (Anttalainen, Tarmo) IntroductoryIntroductory ConceptsConcepts Telecommunication means “communications at a distance” Tele in Greek means at a distance Electrical communications by wire, radio, or light (fiber optics) Traditionally two distinct disciplines: Switching: selects and directs communication signals to a specific user or a group of users Transmission: delivers the signals in some way from source to the far-end user with an acceptable signal quality EE4367 Telecom. Switching & Transmission Prof. Murat Torlak SimpleSimple TransmissionTransmission SystemSystem Source Transmission Medium Destination The source may be a simple telephone microphone, keyboard The destination may be a simple telephone speaker, monitor EE4367 Telecom. Switching & Transmission Prof. Murat Torlak TransmissionTransmission MediaMedia It can be a seen as a single electrical medium Source Medium Destination Or, as a cascade of electrical media Source Medium Medium Medium Destination Networks show a gain or loss. To understand these gains or loss, a good knowledge of the decibel and related measurement units is needed. EE4367 Telecom. Switching & Transmission Prof. Murat Torlak dBdB inin CommunicationsCommunications The db (decibel) is a relative unit of measurement commonly used in communications for providing a reference for input and output levels. Power gain or loss. Decibels are used to specify measured and calculated values in audio systems, microwave system gain calculations, satellite system link-budget analysis, antenna power gain, light-budget calculations and in many other communication system measurements In each case the dB value is calculated with respect to a standard or specified reference.
    [Show full text]
  • The Decibel, Application Note No. 7
    Application Note No. 7 ABCD 1996 Reeve Engineers E The DeciBel 1. Introduction This application note covers the logarithmic unit of signal ratio most commonly used in telephony, the deciBel (dB). Another related application note covers the application of the dB in using Transmission Level Points.1 A sound increase from one power level to another heard by the human ear leaves an impression of increased loudness that is approximately proportional to the logarithm of the ratio of the two powers. The original unit given to this phenomenon was the “Bel.” However, it was not convenient to use and is not seen in practical problems. This gave rise to the “deciBel,” which is Bel/10. A change in power level of 1 dB is barely perceptible to the human ear, while a change of 2 dB is noticeable. A change of 3 dB represents one-half our twice the power. 2. Definition of dB By definition, the deciBel, or dB, is the logarithmic (base 10) ratio of two powers, P1 and P2 given by P dB = 10log 2 P1 Example: Given that P2 = 1 mW and P1 = 0.4 mW, then P2/ P1 = 2.5, and dB = 10log(2.5) = 3.98 dB The sign resulting from the calculation indicates which power is greater. If the sign is positive, then P2 > P1; if negative, then P2 < P1. It is important that the two powers be expressed in the same units, such as milliWatt (mW) or Watt (W), otherwise the calculation is meaningless. If the number of dB is known, the power ratio can be found from P dB dB 2 = Anti log = 10 10 P1 10 1 See Application Note No.
    [Show full text]