‰  NOW 25 WPM  ‰  TEXT IS FROM JANUARY 2016 QST  PAGE 30‰

MHZ LOW PASS FILTER, UP TO A BAND OF FREQUENCIES BETWEEN 100 AND 130 MHZ.
I CHOSE A 100 MHZ UPCONVERSION MIXING SCHEME SO THAT THE FREQUENCY READOUT
ON THE SOFTWARE DISPLAY WILL CORRESPOND TO THE RECEIVED INPUT EXCEPT FOR
THE FIRST DIGIT.  IN OTHER WORDS, A RECEIVED FREQUENCY OF 7R255000 MHZ WILL
BE DISPLAYED AS 107R255000 MHZ.  A SIGNAL AT 10R1 MHZ DISPLAYS AS
110R100000 MHZ, AND SO ON.  THE LOW PASS FILTER IS THREE CAPACITORS AND TWO
T37 2 POWDERED IRON TOROID CORES, EACH WITH NINE TURNS OF 28 AWG ENAMELED
WIRE.  THE LOW PASS 35 MHZ FILTER DESIGN IS NOT THE LEAST BIT CRITICAL YOU
JUST WANT TO FILTER OUT THE FREQUENCIES ABOVE 100 MHZ.  MY JUNK BOX YIELDED
CAPACITOR VALUES WITHIN A FEW OF PICOFARADS OF THE DESIGN VALUES.  NO GAIN
IS NECESSARY IN THIS UPCONVERTER, AS THE DONGLE HAS MORE THAN ENOUGH GAIN
TO COMPENSATE FOR ANY LOSS THROUGH THE FILTER AND MIXER.  CONSTRUCTION THE
FRONT VIEW IN FIGURE 3 SHOWS THE SWITCH S1 THAT ACTIVATES EITHER THE HF OR
‰  END OF 25 WPM TEXT  ‰  QST DE W1AW  ƒ