Was written:
> The dynamic range of a digital system is based on the number
> of binary bits in each word.
> Each bit corresponds to a doubling of the resolution,
> or roughly 6dB of dynamic range capability. Telephone systems
> typically use 8 bits which is approximately 48 dB dynamic range
> linear, although effectively more when companded. Today's CD's
> and most digital recorders use a 16 bit system for some 96 dB of
> dynamic range.
A couple of lines written by Doug Smith about the A/D conversion
within the coming Ten Tec Orion rig:
"State-of-the-art 24-bit IF-DSP converters, such as those used in
the Ten-Tec Orion, produce about 100 dB of dynamic range.
(Note: the theoretical resolution with 24 bits, is 144 dB!)
That
means a receiver can handle signals from the noise floor to almost
40 dB over S9 without analog AGC. Above that level, analog AGC
is still necessary to maintain the linearity of analog circuits and to
prevent overload in the ADC hardware.
Do not be misled by hype about 32- and 64-bit processing. In a
correctly executed design, it is mainly the dynamic range of the
ADC hardware that determines how a receiver will perform in the
presence of crushing QRM.
32-bit ADCs with enough speed and accuracy to handle IF-DSP do
not yet exist and 24-bit resolution is the best available."
And 24 bit chips for A/D are used within the Orion design, state-of
the-art A/D chips, per Doug's piece, see:
http://www.doug-smith.net/dspdynamics.htm
However, even Doug's design seems to "only" realize some
18 or maybe 19 bits of "effective" A/D conversion as just over
100 dB dynamic range is suggested by Doug as what is being
realized in tests. Even if 32 bit A/D chips were available, it
does not mean that that much resolution of the analog conversion
would occur. Important is also the decision made in the
conversion when the amplitude, for example, is "between" sample steps;
does it round up or round down, hi. Lots of little details besides
just the spec claims about the chips themselves.
Whatever, Doug's design, as promised, is the "best" promised
in the amateur rig market so far; we will see in a few weeks
what will actually be delivered and experienced by Orion users.
73, Jim KH7M
|