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23、BLISHED AS TSB-179-A i TABLE OF CONTENTS DOCUMENT REVISION HISTORY ii FOREWORD . iii Patent Identification . iv INTRODUCTION . v 1.0 SCOPE . 1 2.0 BACKGROUND 2 3.0 DEFINITIONS AND ABBREVIATIONS . 3 4.0 SYSTEM VSWR ESTIMATION TOOLS . 4 4.1 Naval Electronic Warfare Handbook . 4 4.2 Early Calculation o
24、f System Return Loss 5 4.3 Improved System Return Loss Calculation Method 6 4.4 Latest System Return Loss Spreadsheet Calculator 8 4.5 Tower Mounted Amplifier Example . 14 5.0 CONCLUSION 15 BIBLIOGRAPHY 16 TABLE OF FIGURES Figure 1 Reduction of VSWR by Attenuation 4 Figure 2 System VSWR Calculator,
25、Perfect Main Feed Line (1.000:1 VSWR) . 9 Figure 3 System VSWR Calculator, Typical Main Feed Line (1.11:1 VSWR) 10 Figure 4 Section 4.3 Example using last version of Spreadsheet Calculator . 11 Figure 5 Newest version of standalone calculation . 12 Figure 6 Expanded view to reveal all steps calculat
26、ed 13 TABLE OF TABLES Table 1 Example comparisons . 11 TIA-PN-179-A TO BE PUBLISHED AS TSB-179-A ii DOCUMENT REVISION HISTORY Version Date Description TSB-179 October, 2003 Original Issue TSB-179-1 July, 2004 Error Corrections TSB-179-A Incorporated TSB-179-1 TSB-179-A iii FOREWORD (This foreword is
27、 not part of this Bulletin) This Bulletin was prepared by TIA Working Group TR-8.11.5 and was approved by TIA Engineering Subcommittee TR-8.11. This document includes no Annexes. The source of much of this Bulletin is acknowledged to be originally from Andrew Corporation which has been acquired by C
28、ommScope. . TIA-PN-179-A TO BE PUBLISHED AS TSB-179-A iv Patent Identification The readers attention is called to the possibility that using this document might necessitate the use of one or more inventions covered by patent rights. By publication of this document no position is taken with respect t
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31、ty or scope of those patents that are brought to its attention. TSB-179-A v INTRODUCTION Return Loss or VSWR sweeps taken at the bottom end of the transmission line are used by systems operators and contractors to determine the condition of the complete RF path including the antenna. For many years,
32、 this RF path consisted of the main transmission line, jumper cables and an antenna. Several calculators were developed to estimate what the expected return loss or VSWR ought to be if all components were meeting specification. Since the antenna was by far the component with the highest VSWR, out-of
33、-specification readings at the bottom end often could be traced to an out-of-specification antenna. However, with the advent of more complex systems incorporating additional devices such as Tower Mounted Amplifiers and Diplexers, the antenna is no longer the only major VSWR contributor in the RF pat
34、h. This Bulletin addresses the issues associated with measuring the complete RF path and offers some suggestions about how to make more meaningful measurements. TSB-179-A 1 Terrestrial Land Mobile Radio - Antenna Systems - Total “Antenna System” Return Loss Measurements 1.0 SCOPE In the land mobile
35、radio service there has historically been no clear relationship between the VSWR specifications of the individual components in the RF path and the expected resultant “system” VSWR at the bottom end of the transmission line. This makes it difficult, at best, for system operators to set a realistic s
36、et of measurement expectations for installers and technicians to use for checking completed installations Various calculators and nomographs have been developed over the years to try to estimate what the expected system VSWR ought to be for the total RF path, but, at best they treat the combination
37、of the individual component VSWR vectors as if they combine in a random fashion. This might be true most of the time, but there might be those instances where random vector combinations do not happen. This Bulletin presents some of the nomographs and calculators that have been employed over the year
38、s and introduces an improved calculator that shows both typical and worst case vector summation. It also presents some theoretical reference material detailing how the VSWRs of specific components might combine. 1. The use of manufacturers names is not an endorsement, rather an acknowledgement to th
39、e source of the material in this Bulletin. TIA-PN-179-A TO BE PUBLISHED AS TSB-179-A 2 2.0 BACKGROUND The terms Voltage Standing Wave Ratio (VSWR), Return Loss (RL), Reflection Coefficient () and Mismatch Loss are all terms used to define the amount of mismatch between an RF source and an RF load; h
40、ence they are a measure of the efficiency of the RF transmission system. They are all mathematically related and can be easily converted using the equations in 3.0,2. Some of the earliest information used for estimating the total system VSWR from the bottom end of the transmission line was presented
41、 as a simple nomograph. Later, calculation methods based on compiled measured data were suggested and they included “multiplication factor” based on data taken on thousands of antenna systems. With the advent of electronic spreadsheets, more complex calculators were developed to take into account al
42、l of the individual components in the RF path along with more specifications associated with the individual components. This approach also allowed for calculation of not only the typical system value where random vector combinations are employed, but also allows for calculation of the worst-case sys
43、tem value where all vectors add together in phase 1. Over the years, an antenna VSWR specification of 1.5:1 (14 dB RL) has been deemed acceptable for most applications. This value equates to 96% forward power transfer or only 4% reflected power. Many system owners have increased this 14 dB return lo
44、ss number by a few dB, which improves the VSWR (e.g., 16 dB RL to include a transmission line contribution) and define it as the total system return loss goal. As the industry progresses to very high-speed data transmission, there is another phenomenon that may need to be considered. For example, th
45、roughput for 64 QAM modulations can be degraded due to distortion. A higher system VSWR translates to reduced modulation fidelity, caused by non-optimal loading of the power amplifier (PA). This concept was introduced as non-optimal PA loading in a NIC by its antenna.7, 8. TSB-179-A 3 3.0 DEFINITION
46、S AND ABBREVIATIONS EVM: Error Vector Magnitude loge: The natural logarithm MHA: Mast Head Amplifier (same as Tower Mounted Amplifier) NIC: Network Interface Card PA: Power Amplifier QAM: Quadrature Amplitude Modulation RF: Radio Frequency RL: Return Loss RF Path: The path an RF signal travels to ge
47、t from the transmitter output until it is radiated by the antenna. This is not to be confused with the propagation loss of the RF path between antennas. TMA: Tower Mounted Amplifier (same as Mast Head Amplifier) VNA: Vector Network Analyzer Equations: VSWR = 11+= 20201 101 10RLRL+= 11RFRFPPPP+(1) Re
48、turn Loss (RL) = 10 10 10110 og 20 og 20 og1FRP VSWRLL LP VSWR = =+(2) Voltage Reflection Coefficient201( ) 101RLRFVSWR PVSWR P= = =+(3) Where: Return Loss(dB)is a positive value 0 1 TIA-PN-179-A TO BE PUBLISHED AS TSB-179-A 4 4.0 SYSTEM VSWR ESTIMATION TOOLS 4.1 Naval Electronic Warfare Handbook Ea
49、rly total system VSWR estimates made use of nomographs like the one shown in Figure 1 below from the Naval Electronic Warfare Handbook2: Figure 1 Reduction of VSWR by Attenuation The results obtained from Figure 1 are somewhat over-simplified in that they do not take into account the VSWR of the attenuator (transmission line). Instead, it simply adds twice the attenuator value (once to get up to the load and a second time to get back to the bottom end) to produce the load VSWR. As an example, a load (antenna) with a 10:1 VSWR connecte
