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MICROWAVE LENGTHS.  LOCAL OSCILLATORS FOR TRANSVERTERS. THE MICROWAVE
LENGTHS COLUMN IN THE JANUARY 2024 ISSUE OF QST DISCUSSED TRANSVERTERS AND
HOW THE LOCAL OSCILLATOR, LO, IS AN ESSENTIAL PART.  THE LO PROVIDES A
SIGNAL TO THE MIXER AT A FREQUENCY THAT IS ADDED TO THE IF SIGNAL TO CREATE
A MICROWAVE SIGNAL FOR TRANSMISSION.  THE LO ALSO PROVIDES A SIGNAL TO THE
MIXER AT A FREQUENCY THAT IS SUBTRACTED FROM THE MICROWAVE FREQUENCY TO
RECEIVE IF SIGNALS ON A VHF OR UHF TRANSCEIVER. FINDING WEAK SIGNALS OR
OPERATING DIGITAL MODES REQUIRES AN LO THAT IS CLEAN, STABLE, AND ON
FREQUENCY, AND HAS LOW PHASE NOISE.  TRADITIONAL LOS STARTED WITH A CRYSTAL
OSCILLATOR, TYPICALLY AROUND 100 MEGAHERTZ.  THEN THE CRYSTAL FREQUENCY WAS
MULTIPLIED THROUGH A SERIES OF FREQUENCY MULTIPLIERS, SUCH AS DOUBLERS,
TRIPLERS, AND QUADRUPLERS, UP TO THE ULTIMATE LO FREQUENCY.  FOR A 10
GIGAHERTZ LO, THE FREQUENCY MIGHT BE MULTIPLIED 96 TIMES OR MORE.  A CRYSTAL
OSCILLATOR USUALLY PROVIDES A VERY CLEAN SIGNAL, BUT MANY MULTIPLIERS CAN
CREATE OFF FREQUENCY LOWER LEVEL SIGNALS THAT CAN REACH THE MIXER AND
PRODUCE UNWANTED SIGNALS. ONE RESULT CAN BE SPURIOUS SIGNALS IN THE
RECEIVER, WHICH CAN BE HARD TO DIFFERENTIATE FROM DESIRED WEAK SIGNALS.
GOOD CRYSTALS NEEDED FOR THE LO FREQUENCIES HAVE BECOME DIFFICULT TO FIND,
SO THE TREND IS TO USE A FLEXIBLE FREQUENCY SYNTHESIZER TO GENERATE LO
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