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Microwave Variable-Frequency Measurements and Applications Telecommunications Microwave Microwave Variable-Frequency Measurements and Applications Courseware Sample 85896-F0 Order no.: 85896-00 First Edition Revision level: 02/2015 By the staff of Festo Didactic © Festo Didactic Ltée/Ltd, Quebec, Canada 2010 Internet: www.festo-didactic.com e-mail: [email protected] Printed in Canada All rights reserved ISBN 978-2-89640-425-4 (Printed version) Legal Deposit – Bibliothèque et Archives nationales du Québec, 2010 Legal Deposit – Library and Archives Canada, 2010 The purchaser shall receive a single right of use which is non-exclusive, non-time-limited and limited geographically to use at the purchaser's site/location as follows. The purchaser shall be entitled to use the work to train his/her staff at the purchaser's site/location and shall also be entitled to use parts of the copyright material as the basis for the production of his/her own training documentation for the training of his/her staff at the purchaser's site/location with acknowledgement of source and to make copies for this purpose. In the case of schools/technical colleges, training centers, and universities, the right of use shall also include use by school and college students and trainees at the purchaser's site/location for teaching purposes. The right of use shall in all cases exclude the right to publish the copyright material or to make this available for use on intranet, Internet and LMS platforms and databases such as Moodle, which allow access by a wide variety of users, including those outside of the purchaser's site/location. Entitlement to other rights relating to reproductions, copies, adaptations, translations, microfilming and transfer to and storage and processing in electronic systems, no matter whether in whole or in part, shall require the prior consent of Festo Didactic GmbH & Co. KG. Information in this document is subject to change without notice and does not represent a commitment on the part of Festo Didactic. The Festo materials described in this document are furnished under a license agreement or a nondisclosure agreement. Festo Didactic recognizes product names as trademarks or registered trademarks of their respective holders. All other trademarks are the property of their respective owners. Other trademarks and trade names may be used in this document to refer to either the entity claiming the marks and names or their products. Festo Didactic disclaims any proprietary interest in trademarks and trade names other than its own. Safety and Common Symbols The following safety and common symbols may be used in this manual and on the equipment: Symbol Description DANGER indicates a hazard with a high level of risk which, if not avoided, will result in death or serious injury. WARNING indicates a hazard with a medium level of risk which, if not avoided, could result in death or serious injury. CAUTION indicates a hazard with a low level of risk which, if not avoided, could result in minor or moderate injury. CAUTION used without the Caution, risk of danger sign , indicates a hazard with a potentially hazardous situation which, if not avoided, may result in property damage. Caution, risk of electric shock Caution, hot surface Caution, risk of danger Caution, lifting hazard Caution, hand entanglement hazard Notice, non-ionizing radiation Direct current Alternating current Both direct and alternating current Three-phase alternating current Earth (ground) terminal Safety and Common Symbols Symbol Description Protective conductor terminal Frame or chassis terminal Equipotentiality On (supply) Off (supply) Equipment protected throughout by double insulation or reinforced insulation In position of a bi-stable push control Out position of a bi-stable push control We invite readers of this manual to send us their tips, feedback, and suggestions for improving the book. Please send these to [email protected]. The authors and Festo Didactic look forward to your comments. )RUHZRUG The Lab-Volt Microwave Technology Training System With LVDAM-MW, Model 8091, is a complete microwave training system including data acquisition and instrumentation that allows students to perform experiments in microwave principles and practices. This Student Manual, Microwave Variable-Frequency Measurements and Applications, is a continuation of the basic principles learned in Microwave Fundamentals. It demonstrates the operation of variable-frequency oscillators. You will learn how to control and measure the operating frequency of a voltage-controlled RF oscillator, using the Lab-Volt software Data Acquisition and Management for Microwave systems (LVDAM-MW®). You will learn how to perform frequency modulation and demodulation of microwave signals to convey useful information, such as data or music, over a microwave link. The Instructor Guide Microwave Variable-Frequency Measurements and Applications provides answers to all procedure steps and review questions found in the exercises of this manual. Note: Detailed information about how to set up and use the instruments of the LVDAM-MW software can be found in the Lab-Volt User Guide "Microwave Data Acquisition and Management", part number 85756-E. Additional information about using these instruments can be found in the Help section of this software. Information about the instruments used to control or monitor the Frequency Meter of the Voltage-Controlled RF Oscillator (VCO), Model 9511, are provided in the Parameter Settings section of the Help. Safety with RF Fields When studying microwave systems, it is very important to develop good safety habits. Although microwaves are invisible, they can be dangerous at high levels or for long exposure times. The most important safety rule when working with microwave equipment is to avoid exposure to dangerous radiation levels. The radiation levels in the Microwave Technology Training System are too low to be dangerous, so that this system allows safe operation in a classroom laboratory. To develop good safety habits, however, you should, whenever possible, remove the power from the Gunn Oscillator before placing yourself in front of the transmitting antenna. Your instructor may have additional safety directives for this system. WARNING! For your safety, do not look directly into the waveguides or Horn Antennas while power is being supplied to the Gunn Oscillator. III 7DEOHRI&RQWHQWV Exercise 1 Microwave Frequency Measurements ................... 1-1 Measuring microwave frequencies, using the slotted-line method, the prescaler method, and the resonant cavity method. Introduction to the Lab-Volt Voltage-Controlled RF Oscillator (VCO). Exercise 2 Microwave Variable-Frequency Oscillators .............. 2-1 Introduction to variable-frequency oscillators. The mechanical and electronic tuning methods. Functional diagram and operation of the Lab-Volt Voltage-Controlled RF Oscillator (VCO). Plotting the VCO output power-versus-frequency curve. Effect that a change in the VCO's frequency has on the power reflected by a load matched at a specific frequency. Amplitude modulation of a VCO's output signal. Exercise 3 Microwave Frequency Modulation and Demodulation ..... 3-1 Conveying information over a microwave link, using frequency modulation of a microwave's output signal. Representation of a microwave FM signal in the time and frequency domains. Demodulation of a microwave FM signal, using a tank circuit connected to a diode detector circuit. Appendices A Common Symbols B Module Front Panels C New Terms and Words D Equipment Utilization Chart Bibliography V Sample Exercise Extracted from Student Manual ([HUFLVH 0LFURZDYH)UHTXHQF\0HDVXUHPHQWV EXERCISE OBJECTIVES When you have completed this exercise, you will be familiar with three methods of measuring microwave frequencies: slotted-line, prescaler, and resonant cavity frequency measurements. DISCUSSION Slotted-Line Frequency Measurements When the impedance of the load is not equal to that of the waveguide, an impedance mismatch occurs. In this case, not all the received energy is absorbed by the load. Instead, part of this energy is reflected back toward the source. Figure 1-1 shows the waves traveling along a waveguide when the load end is in the short-circuit condition. The incident wave is completely reflected at the load end. The reflected and incident waves travel through each other, but in opposite directions, thereby combining vectorially. This results in the creation of a standing wave along the waveguide. Figure 1-1. Creation of a standing wave along a short-circuited waveguide. Figure 1-2 shows the conventional representation of the standing wave of voltage along the short-circuited waveguide. 1-1 0LFURZDYH)UHTXHQF\0HDVXUHPHQWV Figure 1-2. Conventional representation of the standing wave of voltage along the short-circuited waveguide. When we examine Figure 1-2, the statements below can be inferred. These statements allow you to measure the frequency of a microwave signal propagating in a waveguide. • A minimum invariably occurs at the load end of the waveguide. • Minima also occur at every even multiple of Ȝg/4 from the load end (Ȝg being the wavelength of the propagating wave in the waveguide). • Maxima occur at every odd multiple of Ȝg/4 from the load end. To measure the frequency of the microwave signal, the waveguide is coupled to a slotted line terminated by a short circuit. The slotted line is connected to a SWR meter. The microwave signal is amplitude-modulated with a 1-kHz square-wave signal to permit SWR measurements with the slotted line and SWR meter. Then, the following steps
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