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INSTRUCTIONS.  BY SETTING UP THE PLL AND DIVIDERS, YOU CAN CREATE PRECISE
ARBITRARY FREQUENCIES.  THERE ARE THREE INDEPENDENT OUTPUTS, AND EACH ONE
CAN HAVE A DIFFERENT FREQUENCY.  OUTPUTS ARE 3 VP P SQUARE WAVES, EITHER
THROUGH A BREADBOARD FRIENDLY HEADER OR, AN OPTIONAL SMA CONNECTOR.  FOR
THIS PROJECT, THE MODULE SHOULD HAVE AN ONBOARD 25 MHZ CRYSTAL.
CHARACTERISTICS OF WSPR SIGNALS A WSPR SIGNAL IS BASICALLY A FREQUENCY
SHIFT KEYED FSK TONE AND DOES NOT REQUIRE AMPLITUDE LINEARITY.  WE CAN
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UTILIZE THE SI5351 CLOCK WITH SQUARE WAVE OUTPUT.  A FILTER IS THEN ADDED
TO REMOVE HIGHER ORDER HARMONICS INHERENT IN THE SQUARE WAVE.  WSPR SIGNALS
HAVE A BANDWIDTH OF ONLY 6 HZ AND FIT INTO A TINY 200 HZ SEGMENT ON A GIVEN
BAND.  THIS PERMITS SEVERAL TENS OF STATIONS TO COEXIST WITH MINIMAL
INTERFERENCE.  FOR EXAMPLE, THE 30 METER BAND IS CENTERED AT 10R140200 MHZ.
SUCH A NARROW BAND REQUIRES A VERY ACCURATE AND STABLE OSCILLATOR REFERENCE
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