=  NOW 25 WPM  =  TEXT IS FROM JANUARY 2023 QST  PAGE 43 =

WHETHER A RELENTLESS SO2R CONTESTER, A SINGLE RADIO DXER, OR AN EVERYDAY
RAGCHEWER NEEDING A 160 6 METER AUTO TUNING, LEGAL LIMIT ANTENNA TUNER.
BHI DSP NOISE CANCELING IN LINE MODULE REVIEWED BY PAUL DANZER, N1II FROM
THE VERY BEGINNING, RADIO AMATEURS HAVE BEEN TRYING TO PULL WEAK SIGNALS
OUT OF THE ACCOMPANYING NOISE.  THE DESIGNS USED DEPENDED ON THE TECHNOLOGY
AND PARTS AVAILABLE AT THE TIME.  AS AN EXAMPLE, CLIPPING PEAKS AND
REDUCING THE BANDWIDTH WERE INITIALLY ALL THAT WERE AVAILABLE.  LATER, MORE
SOPHISTICATED AND COMPLICATED CIRCUITS WERE USED, SUCH AS THE CURRENT
APPROACH USED FOR SOME UNITS THAT SAMPLE THE NOISE ALONE, USUALLY THROUGH A
SECOND ANTENNA, SO THE NOISE IS CAPTURED BEFORE IT ENTERS THE RECEIVER.
THIS NOISE IS THEN SUBTRACTED FROM THE COMBINED SIGNAL AND NOISE FROM THE
MAIN ANTENNA.  THE EXPECTATION IS THAT SOME, OR HOPEFULLY MOST, NOISE WILL
BE SUBTRACTED OUT.  ANOTHER WAY TO REDUCE, OR HOPEFULLY ELIMINATE, THE
=  END OF 25 WPM TEXT  =  QST DE W1AW  <