‰  NOW 35 WPM  ‰  TEXT IS FROM MAY 2015  QST  PAGE 37 ‰

A 100 HZ TO 10 MHZ SIGNAL GENERATOR  HERE IS A COMPACT GENERATOR WITH A
TOUCHSCREEN AND A COMPUTER INTERFACE.  JIM VEATCH, WA2EUJ  A SIGNAL
GENERATOR IS ONE OF THE MOST USEFUL PIECES OF TEST EQUIPMENT FOR WORKING
WITH AMATEUR RADIO PROJECTS.  EVERY WORKBENCH NEEDS A SIGNAL GENERATOR FOR
INJECTING AN AUDIO SIGNAL TO SET LEVELS IN A TRANSMITTER, OR FOR EVALUATING
RECEIVER SENSITIVITY AND DYNAMIC RANGE, AND SO ON.  THIS ARTICLE DESCRIBES
A DIRECT DIGITAL SYNTHESIS DDS BASED GENERATOR SEE THE LEAD PHOTO, WHICH
FEEDS A VARIABLE GAIN AMPLIFIER AND SWITCHED ATTENUATORS TO GENERATE
SIGNALS FROM 100 HZ TO 10R8 MHZ IN 1 HZ STEPS, AND AT POWER LEVELS FROM 120
DBM TO 0 DBM IN 0R2 DB STEPS.  YOU CAN BUILD THE GENERATOR WITH A COLOR LCD
TOUCHSCREEN INTERFACE, OR WITH A USB INTERFACE FOR COMPUTER CONTROL.  IN
EITHER CONFIGURATION, CONSTRUCTION USES ALL THROUGH HOLE COMPONENTS.  A
PRINTED CIRCUIT BOARD PCB IS AVAILABLE TO MAKE ASSEMBLY EASY.  ALL
COMPONENTS ARE READILY AVAILABLE FROM ONLINE RETAILERS.  THE PC CONTROLLED
VERSION CAN BE BUILT FOR ABOUT 100, AND THE LCD VERSION FOR ABOUT 50 MORE.
THE DESIGN  THE BLOCK DIAGRAM FIGURE 1 SHOWS THE SIGNAL FLOW THROUGH THE
GENERATOR.  THE DDS 25 MODULE HAS A 25 MHZ OSCILLATOR AND AN ANALOG DEVICES
AD9833 DDS CHIP ALREADY MOUNTED AND TESTED.  A SERIAL PERIPHERAL INTERFACE
SPI BUS CONTROLS THE DDS, WHICH CAN GENERATE SIGNALS FROM 100 HZ TO 10R8
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