DOCSLIB.ORG

Induction Coil and Coreless Induction Furnace Employing Same

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

s\ mi mi ii 111 mi ii i inn ii i ii OJII Eur°Pean Patent Office <*S Office europeen des brevets (11) EP 0 858 246 A2 (12) EUROPEAN PATENT APPLICATION (43) Date of publication: (51) int. CI.6: H05B 6/22, H05B 6/36 12.08.1998 Bulletin 1998/33 (21) Application number: 97304802.8 (22) Date of filing: 02.07.1997 (84) Designated Contracting States: • Peysakhovich, Vitaly A. AT BE CH DE DK ES Fl FR GB GR IE IT LI LU MC Moorestown, New Jersey 08057 (US) NLPTSE • Prabhu, Satyen A. Voorhees, New Jersey 08043 (US) (30) Priority: 10.02.1997 US 797148 . Krupnick, Laurence A. Huntingdon Valley, Pennsylvania 19006 (US) (71) Applicant: INDUCTOTHERM CORP. Rancocas, New Jersey 08073-0157 (US) (74) Representative: Perkins, Sarah Stevens, Hewlett & Perkins (72) Inventors: ■! Serjeants' Inn • Fishman, Oleg S. Fleet Street Maple Glen, Pennsylvania 1 9002 (US) London EC4Y 1 LL (GB) • Mortimer, john H. Mt. Laurel, New Jersey (US) (54) Induction coil and coreless induction furnace employing same (57) An induction coil for inductively heating electri- cally conductive materials includes a plurality of individ- ual coil turns, each turn lying in a plane substantially perpendicular to a longitudinal axis of the coil and com- prising an electrical conductor formed into an annulus. The conductor has first and second terminals for con- necting the turn to an electrical circuit. The first and sec- ond terminals are adjacent each other at a preselected circumferential position on the annulus and are physi- cally and electrically isolated from each other. The first terminal of one turn is located adjacent and electrically connected to the second terminal of an adjacent turn. The first terminal of a selected one of the plurality of turns forms a first coil terminal and the second terminal of a different selected one of the plurality of turns forms a second coil terminal. CM < CO CM CO LO CO o Q_ LU Printed by Xerox (UK) Business Services 2.16.3/3.4 1 EP 0 858 246 A2 2 Description shape. Welding or brazing lengths of copper tubing together to make a large enough coil present readily Field of the Invention apparent disadvantages of their own. The pitch of the helical winding, especially when The present invention relates to induction heating 5 large diameter tubing is used in high power furnaces, and melting apparatus, such as for heating and melting causes complications in mounting the coil in the fur- metals, and relates particularly to coreless induction fur- nace, which has flat top and bottom surfaces. naces with an improved coil and magnetic shunt design. In conventional helically wound induction coils, cur- rent flows from the bottom turn to the top turn (or vice Background of the Invention 10 versa) and the returns vertically down (or up) via the ter- mination tube to the bottom (or top) turn. While the mag- Induction heating apparatus such as induction fur- netic field Hc of the coil windings is concentrated inside naces or ladles for heating or melting metals operate on the furnace in the direction of the axis of the coil, the the principle of inducing eddy currents in an object magnetic field H, of the current in the termination tube is (sometimes referred to as the load) to be heated. The 15 spread in the area around the tube in the plane of the eddy currents cause the load to act as its own heat coil turns. This stray magnetic field induces eddy cur- source. Power is generated in the load by resistive heat- rents in surrounding metal objects, causing them to ing caused |>y the eddy currents, according to the well- become heated. known P=l R heating principle. As used herein, "heat- ing" is used broadly to encompass not only raising the 20 Summary of the Invention temperature of a material without causing the material to change state, but also melting, wherein the tempera- One aspect of the invention is an induction coil for ture of a material is raised sufficiently to cause it to inductively heating electrically conductive materials. change state. The induction coil comprises a plurality of individual coil In a typical induction furnace, metal to be heated is 25 turns, each turn lying in a plane substantially perpendic- contained in a crucible, and a generally helical induction ular to a longitudinal axis of the coil and comprising an coil surrounds the crucible. The induction coil is water electrical conductor formed into an annulus. The con- cooled. The crucible is usually made of a ceramic ductor has first and second terminals for connecting the refractory material. The eddy currents are induced in turn to an electrical circuit. The first and second termi- the load by passing a high-frequency alternating current 30 nals are adjacent each other at a preselected circumfer- through the induction coil to generate a time-varying ential position on the annulus and are physically and magnetic field, or induction field. Depending upon the electrically isolated from each other. The first terminal of magnitude and frequency of the alternating current in one turn is located adjacent and electrically connected the induction coil, and on other design considerations, to the second terminal of an adjacent turn. The first ter- the induction field can be used for melting, heating, 35 minal of a selected one of the plurality of turns forms a and/or stirring a quantity of molten metal in the crucible. first coil terminal and the second terminal of a different The induction field can also be used for heat treating selected one of the plurality of turns forms a second coil workpieces, and for other procedures. terminal. In virtually all coreless induction furnaces, the Another aspect of the invention is an induction fur- induction coil is constructed of several turns of heavy 40 nace comprising a refractory vessel for holding a quan- wall copper tubing shaped into the form of a helix. Alter- tity of electrically conductive material to be heated, an nating electrical current is conducted through the coil induction coil generally surrounding the vessel for via termination tubes connected to the top and bottom inductively heating electrically conductive material in turns of the coil. Heat generated in the coil turns is the vessel, and a plurality of magnetic shunt assemblies removed by water pumped through the copper tubing. 45 arranged circumferentially around the induction coil for Often, the same termination tubes are used for to con- directing magnetic flux generated by the induction coil nect the coil to both a cooling water supply and a source to the material to be heated in the vessel. The induction of electrical current. As a practical matter, the termina- coil comprises a plurality of individual coil turns, each tion tubes usually are located near each other at one turn lying in a plane substantially perpendicular to a lon- end of the coil. 50 gitudinal axis of the coil and comprising an electrical The coil is preferably made from one continuous conductor formed into an annulus. The conductor has length of copper tubing, or sections of tubing welded or first and second terminals for connecting the turn to an brazed into one continuous length. One drawback of electrical circuit. The first and second terminals are this method of construction is that is does not have adjacent each other at a preselected circumferential great hoop strength. Another is that it is necessary to position on the annulus and are physically and electri- maintain large inventories of copper tubing for making cally isolated from each other. The first terminal of one coils, and to have machinery for winding the copper tub- turn is located adjacent and electrically connected to ing (which is often of large diameter) into a helical the second terminal of an adjacent turn. The first termi- 2 3 EP 0 858 246 A2 4 nal of a selected one of the plurality of turns forms a first assembly of Figure 8, taken along the lines 9-9 in Figure coil terminal and the second terminal of a different 8. selected one of the plurality of turns forms a second coil terminal. Description of the Invention Yet another aspect of the invention resides in the 5 magnetic yokes used with the induction furnace accord- Referring now to the drawings, wherein like numer- ing to the invention. The furnace includes a plurality of als indicate like elements, there is shown in Figure 1 an magnetic yokes arranged at axially opposite ends of the induction furnace 10 with a conventional helically induction coil and a plurality of magnetic shunts wound induction coil 12 as is known in the art. Induction arranged circumferentially around the induction coil. 10 coil 12 as illustrated in Figure 1 is a conventional two Each magnetic shunt comprises a plurality of lamina- section coil, comprising oppositely wound top section tions arranged in a stack. Each lamination has lateral 12a and bottom section 12b, but induction coil 12 could edges facing the induction coil and lying along a portion equally consist of a single section. As discussed above, of the circumference of a circle having a diameter sub- induction coil 12 is constructed of heavy wall copper stantially equal to the outer diameter of the induction 15 tubing wound helically into a plurality of turns 14. AC coil turns, and each lamination has ends adjacent corre- electric current is connected to each section of the sponding axially opposite ends of the induction coil. At induction coil by means of termination tubes 16 con- least one clamp is provided for holding the laminations nected to the top and bottom turns of the coil.
Recommended publications
  • A Computer Simulation of Induction Heat Treating Systems Is Discussed

    A Computer Simulation of Induction Heat Treating Systems Is Discussed

    Optimal Design of Internal Induction Coils Dr. Valentin Nemkov(1), Eng. Robert Goldstein (1), Dr. Vladimir Bukanin(2) (1)Centre for Induction Technology, Inc. 1388 Atlantic Blvd. Auburn Hills, MI 48326 USA www.induction.org (2)St. Petersburg Electrotechnical University (SPbETU), Prof. Popova str., 5, 197376, St. Petersburg, Russia ABSTRACT Internal induction heating coils are not so well studied as external. Three main induction coil styles were proposed in pioneering works many years ago: Cylindrical coils, Hair-pin coils and Rod-type coils [1, 2]. It was clear from the very beginning that electromagnetic parameters of the coils of two first styles might be strongly improved by application of magnetic cores. However it was not clearly shown what parameters may be improved and how much, as well as what are the optimal designs of induction coils. Current presentation contains short consideration and comparison of all three styles of coils followed by a detailed analysis of cylindrical internal (ID) coils using modern computer simulation tools. It is shown that it isn’t sufficient to only consider the influence of magnetic core on electrical efficiency of the coil head. The cores reduce dramatically current demand for transfer of required power into the workpiece. In turn it results in strong reduction of voltage drop and power losses in the whole supplying circuitry: coil leads, busswork and matching transformer. Plus much smaller capacitor battery is required. Computer simulation is simple for single-turn cylindrical ID coils and several computer packages may be used. Computer simulation of multi-turn cylindrical ID coils, which are the most common, is a much more complicated task, due to the return leg.
  • Download (PDF)

    Download (PDF)

    Nanotechnology Education - Engineering a better future NNCI.net Teacher’s Guide To See or Not to See? Hydrophobic and Hydrophilic Surfaces Grade Level: Middle & high Summary: This activity can be school completed as a separate one or in conjunction with the lesson Subject area(s): Physical Superhydrophobicexpialidocious: science & Chemistry Learning about hydrophobic surfaces found at: Time required: (2) 50 https://www.nnci.net/node/5895. minutes classes The activity is a visual demonstration of the difference between hydrophobic and hydrophilic surfaces. Using a polystyrene Learning objectives: surface (petri dish) and a modified Tesla coil, you can chemically Through observation and alter the non-masked surface to become hydrophilic. Students experimentation, students will learn that we can chemically change the surface of a will understand how the material on the nano level from a hydrophobic to hydrophilic surface of a material can surface. The activity helps students learn that how a material be chemically altered. behaves on the macroscale is affected by its structure on the nanoscale. The activity is adapted from Kim et. al’s 2012 article in the Journal of Chemical Education (see references). Background Information: Teacher Background: Commercial products have frequently taken their inspiration from nature. For example, Velcro® resulted from a Swiss engineer, George Mestral, walking in the woods and wondering why burdock seeds stuck to his dog and his coat. Other bio-inspired products include adhesives, waterproof materials, and solar cells among many others. Scientists often look at nature to get ideas and designs for products that can help us. We call this study of nature biomimetics (see Resource section for further information).
  • A Fresh Look at Induction Heating of Tubular Products

    A Fresh Look at Induction Heating of Tubular Products

    htprof.qxd 5/2/04 1:22 PM Page 1 he extensive use of metal tubing A fresh look at in thousands of products de- Tube T mands a wide range of process concepts. For example, in automotive induction heating manufacturing alone, new applica- Solid cylinder tions for tubing are being advanced at High coil efficiency for of tubular products: an expanding rate. These typically solid cylinder small- and medium-size tubular parts Coil efficiency Part 1 include stabilizer bars, intrusion High coil efficiency for beams, structural rails, steering hollow cylinder columns, axles, and shock absorbers. F F F The air conditioning and refrigeration 1 2 Frequency 3 industries and oil- and gas-transmis- Fig. 1 — Conditions for maximizing the elec- sion lines have high-pressure require- trical efficiency of the induction coil are different ments where larger tubular prod- for tubes and solid cylinders, as shown by these ucts are used. In all of these plots of coil efficiency vs. frequency. (Ref. 1) PROFESSOR applications, induction heat- ing has proven effective. the optimal frequency, which corre- INDUCTION Although there are many sponds to maximum coil electrical ef- Valery I. Rudnev • Inductoheat Group similarities, there are several process ficiency, is shifted toward lower fre- features and physical phenomena quencies (frequencies between F1 and Professor Induction wel- that distinguish induction heating of F2 for tubes instead of between F2 and 1 comes comments, ques- tubular products from induction F3 for solid cylinders). The optimal tions, and suggestions for heating of solid cylinders. The condi- frequency for heating tubes (hollow future columns.
  • Handbook of Induction Heating Theoretical Background

    Handbook of Induction Heating Theoretical Background

    This article was downloaded by: 10.3.98.104 On: 28 Sep 2021 Access details: subscription number Publisher: CRC Press Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: 5 Howick Place, London SW1P 1WG, UK Handbook of Induction Heating Valery Rudnev, Don Loveless, Raymond L. Cook Theoretical Background Publication details https://www.routledgehandbooks.com/doi/10.1201/9781315117485-3 Valery Rudnev, Don Loveless, Raymond L. Cook Published online on: 11 Jul 2017 How to cite :- Valery Rudnev, Don Loveless, Raymond L. Cook. 11 Jul 2017, Theoretical Background from: Handbook of Induction Heating CRC Press Accessed on: 28 Sep 2021 https://www.routledgehandbooks.com/doi/10.1201/9781315117485-3 PLEASE SCROLL DOWN FOR DOCUMENT Full terms and conditions of use: https://www.routledgehandbooks.com/legal-notices/terms This Document PDF may be used for research, teaching and private study purposes. Any substantial or systematic reproductions, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The publisher shall not be liable for an loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. 3 Theoretical Background Induction heating (IH) is a multiphysical phenomenon comprising a complex interac- tion of electromagnetic, heat transfer, metallurgical phenomena, and circuit analysis that are tightly interrelated and highly nonlinear because the physical properties of materi- als depend on magnetic field intensity, temperature, and microstructure.
  • Concerning the Design of Capacitively Driven Induction Coil Guns

    Concerning the Design of Capacitively Driven Induction Coil Guns

    IEEE TRANSACTIONS ON PLASMA SCIENCE. VOL. 17. NO. 3. JUNF 19x9 429 Concerning the Design of Capacitively Driven Induction Coil Guns Abstract-This paper is concerned with the design of capacitively 11. THEORYAND SIMULATIONMODEL driven, multisection, electromagnetic coil launchers, or coil guns, tak- A. Capacitively Driven Coil-huncher System ing their transient behavior into account. A computer simulation based on the viewpoint of lumped parameter circuits is developed to predict Fig. 1 is a sketch of a capactively driven, multisection the performance of the launcher system. It is shown that a traveling coil launcher which consists of two main parts: The barrel electromagnetic wave can be generated on the barrel by the resonance and the projectile. It may be driven either by a set of ca- of drive coils and their capacitors. More than half of the energy ini- pacitors, as indicated in the diagram, or, alternatively, by tially stored in the capacitor bank can be converted into kinetic energy a set of ac polyphase sources. The barrel is a linear array of the projectile in one shot, and an additional quarter can be utilized in subsequent shots, if the launcher dimensions, resonant frequency, of drive coils. The projectile is a conducting sleeve sur- and firing sequence are properly selected. The projectile starts smoothly rounding the payload. The drive coils on the barrel are from zero initial velocity and with zero initial sleeve current. Section- energized with a certain time sequence so as to generate to-section transitions which have significant effects on the launcher a traveling electromagnetic wave that interacts with a sys- performance are also discussed.
  • Gases in Metals: Ii. the Determination of Oxygen and Hydrogen in Metals by Fusion in Vacuum

    Gases in Metals: Ii. the Determination of Oxygen and Hydrogen in Metals by Fusion in Vacuum

    S5I4 GASES IN METALS: II. THE DETERMINATION OF OXYGEN AND HYDROGEN IN METALS BY FUSION IN VACUUM By Louis Jordan and James R. Eckman ABSTRACT Nearly all metals contain small amounts of oxygen, hydrogen, and nitrogen, frequently spoken of as "gases in metals," whether or not they exist as oxides, hydrides, and nitrides or in some other form. Many differences in quality of metals not readily attributed to differences in composition, as determined by the usual chemical analyses, or to different physical treatments are supposed to be due to the presence of "gases" in the metals. Satisfactory and generally applicable methods for determining oxygen in metals have not been available. Experimental studies were made of methods of fusion employed in previous vacuum fusion methods. Direct fusion of low- carbon iron alloys in refractory-oxide crucibles, or fusion with antimony tin in similar crucibles, does not determine all of the oxygen present in the metal. In the first case there is the additional difficulty of reduction of the refractory oxides by the carbon in the steel. In the fusion of high-carbon iron alloys this reaction between refractory oxides and carbon of the metal is very pronounced in direct fusion of the metal and is sufficient, even in fusion with antimony tin, to give values for oxygen in excess of the true oxygen content of the metal. Fusion of the metal sample in a graphite crucible permits satisfactory determination of oxygen in both low-carbon and high-carbon alloys. A new vacuum fusion procedure for the determination of oxygen and hydrogen in metals was developed.
  • High Voltage Ignition Moved Back In

    High Voltage Ignition Moved Back In

    Rambling on about Ignition - High Voltage for Model Engine Ignition Article 3, 3/27/2007, © David Kerzel 2007 Rambling on about Ignition - High Voltage High voltage or high tension ignition was the first electric ignition used in engines. Ruhmkorff coils which are “buzz” coils originally made for electrical experiments were used. The Ruhmkorff coils were too fragile for practical engine operation and low voltage ignition was the preferred ignition on early engines. As time went on, higher reliability ignition was needed and high voltage ignition moved back in. The primary focus here is how these systems work electrically. In the last rambling, we examined how low voltage or low tension ignition works and how the coil stores energy and makes the spark or arc when the ignition contacts are opened. High voltage ignition is a continuation of those concepts. As you recall, the current flowing through the coil stores energy in the magnetic field around the coil and releases it when the switch interrupter or points are opened suddenly, causing an arc or spark as the energy stored in the coil is released. Michael Faraday made the first transformer in 1831 but thought it had no practical use. In 1836, Nicholas Callan invented the first induction coil to produce high voltage that was later improved by Heinrich Ruhmkorff in about 1851. In 1860 Lenoir was building spark ignition engines using Ruhmkorff coils. We need to start with a simple automotive type ignition coil which is a transformer. A transformer is two or more coils of wires that share a common magnetic field.
  • 2J 4 INASA CR OR TMX OR AD NUMBER) ICATEOORYI GPO PRICE $ Z ' OTS PRICEIS) $

    2J 4 INASA CR OR TMX OR AD NUMBER) ICATEOORYI GPO PRICE $ Z ' OTS PRICEIS) $

    .. s NASA TECHNICAL NOTE NASA TN D-2717 I h c cy 7 (ACCESSION NUMBER) (THRUI = i /q /> *. IPAOESI ICODE t 45 mi 2J 4 INASA CR OR TMX OR AD NUMBER) ICATEOORYI GPO PRICE $ z ' OTS PRICEIS) $ Hard copy (HC) Microfiche (MF) EXPERIMENTS ON INDUCTIVE AND CAPACITIVE RADIOFREQUENCY HEATING OF A HYDROGEN PLASMA IN A MAGNETIC FIELD by Clyde C. Swett Lewis Research Center Clevekznd, Ohio NATIONAL AERONAUTICS AND SPACE ADM NISTRATION WASH NGTON, D. C. MARCH 1965 * I NASA TN ~-2m L EXPERIMENTS ON INDUCTIVE AND CAPACITIVE RADIOFREQUENCY HEATING OF A HYDROGEN PLASMA IN A MAGNETIC FIELD By Clyde C. Swett Lewis Research Center Cleveland, Ohio NATIONAL AERONAUTICS AND SPACE ADMINISTRATION For sale by the Office of Technical Services, Department of Commerce, Washington, D.C. 20230 -- Price $1.00 EXPEKI"TS ON INDUCTIVE AND CAPACITIVE RADIOFREQUENCY HEATING OF A HYDROGEN PLASMAIN A MAGNETIC FIELD* by Clyde C. Swett Lewis Research Center SUMMARY Experimental results for heating a plasma by a radiofrequency (rf) coil having an ungrounded electrostatic shield are analyzed by using an electric- circuit model based mainly on the geometric character of the apparatus. This model indicates that the presence of a plasma adds a "lossy" capacitor in parallel with the rf coil. Consequently, power goes into the plasma both in- ductively (Ee) and electrostatically (%!Ez). It is believed that the electro- static mode of power transfer is responsible for some anomalies noted in plasma experiments. The amount of power in each mode was calculated and shown to vary with magnetic field. The inductive power transfer increased at magnetic-field values near the atomic and molecular ion cyclotron fields, whereas the electro- static power decreased or increased depending on which parameter - power or coil voltage - was held constant.
  • Practical Transformer Handbook

    Practical Transformer Handbook

    Practical Transformer Handbook Practical Transformer Handbook Irving M. Gottlieb RE. <» Newnes OXFORD BOSTON JOHANNESBURG MELBOURNE NEW DELHI SINGAPORE Newnes An Imprint of Butterworth-Heinemann Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wildwood Avenue, Woburn, MA 01801-2041 A division of Reed Educational and Professional Publishing Ltd S. A member of the Reed Elsevier pic group First published 1998 Transferred to digital printing 2004 © Irving M. Gottlieb 1998 All rights reserved. No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England WIP 9HE. Applications for the copyright holder's written permission to reproduce any part of this publication should be addressed to the publishers British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN 0 7506 3992 X Library of Congress Cataloguing in Publication Data A catalogue record for this book is available from the Library of Congress DLAOTA TREE Typeset by Jayvee, Trivandrum, India Contents Preface ix Introduction xi 1 An overview of transformer sin electrical technology 1 Amber, lodestones, galvanic cells
  • On the Construction of Tesla Transformers Period of Oscillation and Self-Inductance of the Coil

    On the Construction of Tesla Transformers Period of Oscillation and Self-Inductance of the Coil

    1 On the construction of Tesla transformers Period of oscillation and self-inductance of the coil. (Zur construction von Teslatransformatoren. Schwingungsdauer und Selbstinduction von Drahtspulen) By P Drude1 Annalen der Physik, 1902, vol. 314 (4th series, vol. 9), Part I. issue 10, p293-339 + Plate 1, Part II. issue 11, p590-610. Translated by David W Knight2, and Robert S Weaver3. 13th May. 2016. Added by the translators: Table of Contents Translator's commentary.......................................................................................................................2 Notes on the translation........................................................................................................................3 Introduction ........................................................................................................................................4 I. Oscillation period of wire coils ................................................................................................5 1. Experimental method ....................................................................................................................5 2. Transfer to large coils of the results obtained on small coils .......................................................10 3. Effect of the nature of the coil core and and its area on the self-resonance period .....................10 4. Effect of wire insulation on the self-resonance period of the coil ...............................................14 5. Coils with uneven pitch ...............................................................................................................15
  • Vlf Antennas

    Vlf Antennas

    VLF ANTENNAS by Evren EKMEKÇİ Middle East Technical University – May 2004 VLF Band (I) VLF (Very Low Frequency) Band take place from 3 kHz to 30 kHz in the frequency spectrum. Middle East Technical University – May 2004 VLF Band (II) Question: Why do we use VLF Band? Answer: Increased demand for very reliable long range communication and navigation systems caused to use of VLF band. Middle East Technical University – May 2004 VLF Band (III) EM waves penetrate well in the sea water. Low atmospheric attenuation. Appropriate for long range communication. Skin Effect High background noise levels. Communication needs large amount of power at the output of the transmitter. Middle East Technical University – May 2004 VLF Antennas They operates on VLF Band. They are electrically small. This simplifies analysis. They are physically large structures. Generally have a number of towers 200-300 m high. Generally cover areas of up to a square kilometer or more. Support worldwide communicatipn. The principal objective is to radiate specified amount of power over a sufficient bandwidth of frequency. Middle East Technical University – May 2004 Problems with VLF Antennas Bandwidth is less than 200 Hz. Small radiation resistance. They are expensive structures. Antenna system covers a large area. Designing an efficient transmitting antenna is difficult. High power levels are needed for transmission. Middle East Technical University – May 2004 Vertical Electric Monopole Antenna -Antenna Model- Middle East Technical University – May 2004
  • How Spark Transmitters Work by Hal Kennedy, N4GG

    How Spark Transmitters Work by Hal Kennedy, N4GG

    How Spark Transmitters Work by Hal Kennedy, N4GG [This article was written in support of “The History of QST, Volume 1 – Technology” published by the ARRL and available at www.arrl.org/shop.] Pondering spark transmitter operation is, at best, an infrequent occurrence among today’s amateurs. It shouldn’t be however, because in addition to the historical significance of our original methods, virtually all of us own and operate one or more spark rigs today. If you drive a gasoline-powered car - or even if you don’t - you have listened to the ignition noise from one. What is that noise? It is the broad spectrum electromagnetic (EM) wave propagation from a spark gap. Every time a spark plug fires, that electrical impulse excites the ignition wiring in the vehicle – an antenna – which radiates an EM wave; sometimes with considerable power, to considerable distance and over a very broad range of frequencies. Figure 1. Diagram of a 1900 spark gap transmitter A modern car uses the exact components found in a 1900 spark transmitter; a battery, an induction coil to step up Basic operation is straightforward. Close the key and the to high voltage (ignition coil), a spark gap (spark plug) induction coil’s output rises to a sufficient voltage to and an antenna (ignition wiring). All that’s missing is a begin and then maintain an arc across the spark gap. But telegraph key. how does this create an EM wave we can transmit? If we grounded the car’s chassis, connected an antenna The spark gap itself is an electronic switch.