I disagree. There is nothing in the circuits of the diode detector and
the modern product detector that has any phase setting of the audio
recovered signal. If anything, the product detector (a good mixer,
nothing more, nothing less) is better at preserving signal qualities.
The diode detector with injected BFO tends to have limited dynamic range
and great distortion.
There is nothing in the ear to detect relative phase between different
frequencies. There is some capability of detecting relative phase
between the same frequencies arriving at both ears. This explanation
doesn't apply binaural hearing.
There are major differences in relative phase across the typical
Tchebyshev response crystal filter and the relative phase of the IF
strip using under coupled IF transformers. The Tchebyshev response
filters tend to ring badly, while the under coupled IF transformers
don't. Data (FSK or PSK) passed through Tchebyshev filters tends to be
destroyed it if uses most of the pass band. Bessel or Butterworth
response filters tend to have a far better phase response and to ring
far less. The ladder filters used in recent TenTecs tend to have rounded
amplitude response shoulders and to ring far less than the
crystal/mechanical Tchebyshev filter responses. Filter design emphasis
on "filter factor" of square corners and extremely steep slopes creates
filters with rotten time response, that ring which hit by transients,
turning lightning and switch clicks into crashes and line noise from
buzz into continuos noise. These filters destroy digital data. But are
considered to not affect signals detected by ear otherwise because the
ears aren't sensitive to the relative phase of different frequencies.
73, Jerry, K0CQ
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Entire content copyright Dr. Gerald N. Johnson. Reproduction by
permission only.
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