[AMRadio] Receivers

John Coleman ARS WA5BXO wa5bxo2005 at pctechref.com
Sat Jul 29 01:24:43 EDT 2006

The 74A4 excels in stability, dial accuracy, and easy of tuning, but it is
poor on fidelity.   Not just in the audio stages but the conversion and IF
stages add distortion as well.  It's far from the worst of communication
type receivers though, and some might say it's not bad at all, but it
doesn't compare to the Superpros and that vintage of receiver.  You might
want to consider adding a double balanced product detector to one of the
older receivers such as your NC183 for easy of tuning SSB and CW.  There are
a number of different designs that work well by sampling the IF before the
detector.  There is even a chip specially designed for the application and
used in AM stereo radios.   One advantage to this is the enhanced audio
achieved while using the "carrier lock on AM" capability of the quadrature
double balanced product detector.  I used one that I built years ago on my
HQ145, before the special chip was available.  It was a real pleasure not
having to listen to the distortion caused by selective QSB when the carrier
phases out.  It would how ever detect the 60 CPS FM/phase modulation of an
old BC610 VFO where the diode detector did not.



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