--- In softrock40@..., KY1K <ky1k@p...> wrote:
OK, now I'm really confused...........
Oh, and remember: Shannon's Theorem only addresses bandwidth, not
absolute frequency. Having the signal sampled in quadrature means the
phase of the signal is disambiguated, since the I and Q parts are
Hilbert Transforms of one another (all frequencies are 90 degrees out
of phase with one another), and therefore they have different
symmetries around 0.
With real signals, which have even symmetry, you don't know which is
positive and which is negative -- they're effectively the same whether
you regard time as running forward or backward. With complex signals,
you know which direction is earlier and which is later. (That, btw, is
one theoretical reason for preferring complex sampling. Signals in
quadrature are much easier to deal with when they include
time-dependent modulation and transients.)
That means that positive and negative frequencies are not mirrors of
one another, as they are with real-only sampling. The total bandwidth
is still 48kHz, so the frequency excursion is +/-(48/2)kHz.
73
Frank
AB2KT
