‰  NOW 35 WPM  ‰   TEXT IS FROM JANUARY 2014 QST  PAGE 46‰

A MODERN KEYED VFO FOR VINTAGE TRANSMITTERS YOUR CLASSIC TRANSMITTER CAN
RIVAL THE SIGNAL QUALITY OF A MODERN TRANSCEIVER WITH THIS VFO.  FOR
STRAIGHT KEY NIGHT, I WANTED TO PUT MY 50 YEAR OLD EICO 720 TRANSMITTER ON
THE AIR, WITH THE CONVENIENCE OF A VFO RATHER THAN CRYSTAL CONTROL.  I
WANTED THE FEATURES OF A MODERN VFO DIGITAL FREQUENCY READOUT, MEMORIES,
AND FREEDOM FROM DRIFT AND CHIRP.  I DESIGNED A VFO BASED ON THE N3ZI KITS
DDS 2 DIRECT DIGITAL SYNTHESIZER KIT.  IT FEATURES DIGITAL READOUT, 12
MEMORIES, AND FREQUENCY RESOLUTION TO 1 HZ.  IT ALSO MAKES A GREAT SIGNAL
GENERATOR.  VFO OVERVIEW MY EICO 720 TRANSMITTER HAS A SPECIAL INPUT FOR AN
EXTERNAL VFO.  IF YOUR TRANSMITTER LACKS SUCH AN INPUT, YOU CAN PROBABLY
FEED THE VFO SIGNAL DIRECTLY INTO THE CRYSTAL SOCKET WITHOUT MAKING ANY
CHANGES TO THE TRANSMITTER.  REGARDLESS, THE OUTPUT OF THE N3ZI SYNTHESIZER
MUST BE AMPLIFIED, AND SOME SORT OF KEYING CIRCUIT MUST BE ADDED.  I
MOUNTED ALL OF THE COMPONENTS FOR MY VFO EXCEPT THE KEYING CIRCUIT
COMPONENTS IN A STEEL RADIOSHACK PROJECT BOX SHOWN IN FIGURE 1.  FIGURE 2
SHOWS THE DDS BOARD, BUFFER AMPLIFIER, AND KEYING INPUT.  I WANTED TO USE
THE SYNTHESIZER BOTH AS A VFO AND AS A SIGNAL GENERATOR, SO I MADE
PROVISIONS FOR BYPASSING THE BUFFER AMPLIFIER AND KEYING CIRCUITS.  FIGURE
3 SHOWS THE INSIDE OF THE VFO PROJECT BOX.  THE DDS BOARD UPPER CENTER
‰  END OF 35 WPM TEXT  ‰  QST DE W1AW  ƒ