Tech Directions - December 2008 - (Page 22)

Go International! Build a Simpified Shortwave Receiver By Clarke Homoly chomoly@ucmo.edu UILDING a shortwave receiver from scratch, that has reasonable performance, can be a daunting task. Here is a plan for a shortwave receiver that is both doable and educational. The project can give your students years B dozens of other governmental voices. The National Institute of Standards stations broadcast time and frequency reference signals. An amazing variety of AM stations fall between 5 and 22 MHz. Changing a pair of coils in the circuit will allow for exploration of the entire frequency range. to expand their horizons by moving into the major ﬁeld of wireless communication. Getting Started Because of the difﬁculty in obtaining certain critical parts, few people attempt to construct communication receivers these days. Much of the problem is solved in this project because 80% of the receiver uses an old AM broadcast band receiver that you can easily ﬁnd at a garage sale for a very low cost. The i-f ampliﬁer, detector, and audio amp from the old receiver form the heart of the shortwave receiver. All students must build is a chassis and a new frequency converter to tune in the world. A 12"-long aluminum chassis with a piece of ﬁberglass circuit board serving as a front panel would work well. Remove the AM radio from its plastic case and place it on an insulating sheet at one end of the chassis. The front panel will have plenty of room to mount a new on-off switch, volume control, and large speaker. Once the old radio has been wired up to its new chassis, turn it on to see if it still tunes the old 540-1700 kHz band as it should. Front (at left) and back views of the shortwave receiver of listening fun without a major ﬁnancial investment. Electronics teachers have access to a wide variety of factory kits to hand to students, but sometimes having them just plug parts into factory-designed circuit boards leaves something to be desired. Breadboarding circuits on proto-boards is far more educational, but once the project is ﬁnished, the circuit often seems to come apart as fast as it went together. As we know, many components do not lend themselves to this sort of assembly. Several available international broadcast shortwave bands will allow students to listen to the BBC, the Voice of America, Radio Moscow, and Clarke Homoly is associate professor, Department of Aviation, University of Central Missouri, Warrensburg. I’d like to add here that I think a current weakness in the state of electronics education is a shortage of teachers who teach wireless communication. Few have much training in the area and thus fear delving into it. We all tend to stick to the familiar, which to many means working only with logic gates and digital controls. I hope that this article will encourage electronics teachers and students Modifications You will now need to identify the primary of the ﬁrst i-f transformer 22 techdirections ◆ DECEMBER 2008

Table of Contents Feed for the Digital Edition of Tech Directions - December 2008

Tech Directions - December 2008 Contents Advertisers Index Technically Speaking Direct from Washington The Report Technology Today Technology’s Past Mastering Computers Digital Portfolios—Powerful Marketing Tool for Communication Students Choosing the Right CC Welding Unit—Student Success Depends on It Think Green—Increasing Awareness of Garbage and Recycling Think Green—Teach Students Smart Ways to Reduce Home Energy Use Go International! Build a Simplified Shortwave Receiver Mooresville Middle School Snags Web Site of the Month Gifts for Geeks More than Fun

Tech Directions - December 2008

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