‰  NOW 25 WPM  ‰  TEXT IS FROM DECEMBER 2006 QST  PAGES 29, 31 AND 92  ‰
PROVIDES A 50 O SOURCE OF BROADBAND DRIVE TO THE QUADRATURE HYBRID AND
ISOLATES THE FREQUENCY GENERATOR FROM IMPEDANCE VARIATIONS AT THE MIXER
LOCAL OSCILLATOR LO PORTS.  THE SIMPLE ARRANGEMENT USED IN THE MICROR2
RECEIVER DOESNT WORK HERE, BECAUSE HIGH LEVEL AUDIO INTO THE DIODE RING
MIXERS MODULATES NOT JUST THE SIGNAL AT THE RF PORT, BUT THE IMPEDANCE AT
THE LO AND IF PORTS AS WELL.  EXPERIMENTS CONFIRM THAT A DIRECTLY CONNECTED
VFO EXPERIENCES SEVERE FREQUENCY PULLING ON VOICE PEAKS.  THE GAIN OF THE
BUFFER IS SET TO PROVIDE 7 DBM DRIVE TO EACH MIXER WITH AN INPUT LEVEL OF 0
DBM.  IT DRAWS SOME CURRENT AND THE TRANSISTOR GETS A LITTLE WARM BUT ONLY
WHILE TRANSMITTING.  QUADRATURE HYBRID THIS IS A VENERABLE CIRCUIT FIRST
DESCRIBED BY REED FISHER IN QST.  IT IS THE LUMPED ELEMENT EQUIVALENT OF A
PAIR OF TIGHTLY COUPLED QUARTER WAVELENGTH TRANSMISSION LINES.  THE TOTAL
‰  FROM PAGE 92  ‰
1 52 NTX KS2FHN 24 2 1 48 WNY KT4JF 23 2 1 46 EPA K7II 16 2 1 32 IL K5PE 15
‰  END OF 25 WPM TEXT  ‰  QST DE W1AW  ƒ