‰  NOW 35 WPM  ‰   TEXT IS FROM JANUARY 2014 QST  PAGE 48‰

VFO RIT KEYING AND FINAL WIRING THE RITB INPUT ON THE SYNTHESIZER BOARD IS
PROGRAMMED SO THAT THE VFO IS ON FREQUENCY WHEN THE INPUT IS OPEN, AND OFF
FREQUENCY WHEN THE INPUT IS CONNECTED TO GROUND.  TRANSISTOR Q5 INVERTS THE
RIT KEYING SIGNAL FROM Q4 IN THE KEYING CIRCUIT, AND ALSO PROTECTS THE RITB
INPUT ON THE SYNTHESIZER BOARD FROM EXCESSIVE VOLTAGES THAT MIGHT BE
ACCIDENTALLY CONNECTED TO THE EXTERNAL RIT KEYING INPUT.  FIGURE 2 SHOWS
THE VFO BLOCK DIAGRAM.  TRANSISTOR Q5 IS TURNED ON BY THE BASE CURRENT
THROUGH THE 4R7 K RESISTOR WHEN THE KEY IS UP, SINCE Q4 IS TURNED OFF AND
THE EXTERNAL RIT KEYING INPUT IS EFFECTIVELY OPEN.  DURING KEY DOWN, Q4 IS
TURNED ON AND THE EXTERNAL RIT KEYING INPUT IS SHORTED TO GROUND, CUTTING
OFF THE BASE CURRENT TO Q5, TURNING IT OFF.  THIS OPENS THE RITB LINE ON
THE SYNTHESIZER BOARD AND BRINGS THE SYNTHESIZER ON TO THE TRANSMIT
FREQUENCY.  A SPOT SWITCH IS USED BETWEEN Q5 AND THE RITB INPUT ON THE
SYNTHESIZER BOARD.  WHEN THIS SWITCH IS OPEN, THE RITB LINE IS
DISCONNECTED, THE SYNTHESIZER IS BROUGHT ON FREQUENCY, AND THE RIT KEYING
IS DISABLED.  THIS ALLOWS YOU TO SET THE VFO TO THE FREQUENCY YOU WANT BY
SPOTTING IT ON YOUR RECEIVER.  TUNE THE VFO UNTIL THE FREQUENCY MATCHES THE
RECEIVED SIGNAL.  MOUNT THIS SWITCH SO THAT UP IS OFF, AND DOWN IS ON.  THE
SWITCH WILL NORMALLY BE IN THE DOWN ON POSITION, AND SWITCHED UP TO SPOT
‰  END OF 35 WPM TEXT  ‰  QST DE W1AW  ƒ